Talk:Speed of light/Archive 12

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Faster than c signals

I added the Scharnhorst effect as explained in this article:

http://arxiv.org/abs/gr-qc/0107091v2

Dicklyon seems to have problems, not sure why. The previous version of the section was wrong, as it made the statement that it is accepted that faster than light signals are always impossible. That's certainly not the case, given the Scharnhorst effect. Count Iblis (talk) 02:25, 17 October 2009 (UTC)

Your edit said:

The Scharnhorst effect is the only known effect allowing information or energy to travel faster than c.

referencing: S. Liberati S. Sonego, and M. Visser , Faster-than-c signals, special relativity, and causality, Annals Phys. 298, 167-185 (2002) preprint

So I downloaded the source to see whether it claimed such an effect, and if so whether it claimed it was the only one. I didn't find support for either. The word "information" appeared only in a reference title, if I'm not mistaken. If I'm wrong, please point out what in this ref you're relying on for these statements. As to whether the previous version was correct or not, I have no knowledge or opinion; but I think we need to base what we say on sources. According to Faster than light, citing this source, that effect is probably bogus, so if you want to add it, you'll probably need to add both points of view on this remote possibility. Dicklyon (talk) 02:37, 17 October 2009 (UTC)

Sorry, you have to actually read the entire article. It is not possible to give a direct quote in this case as the section in which the Scharnhorst effect is treated assumes that you've read the previous pages. The article http://arxiv.org/abs/0706.0553 is not a rigorius rebuttal of the effect (again, did you actually read that article?). Count Iblis (talk) 03:05, 17 October 2009 (UTC)

You can't show us where your source supports your statement? I have to read the whole article? I don't think that works for me. But if some other editor will check and tell me that those two parts of your statement are verified therein, I'll let it go. As for the contrary POV, no, I hardly looked at the abstract on that one; but it's an alternate point of view, is it not? Doesn't that mean that we can't report as fact the result that information can be transmitted faster than the speed of light via that effect? Dicklyon (talk) 03:28, 17 October 2009 (UTC)

The contrary POV is not a bona fide rebuttal. Heidi raises some questions about the way dispersion relations were used in the derivation without proving that an error really has been made. She then goes on assuming that the effect is real and showing that it is too small to be measured. Her article was not published in a more prominent journal, which would be strange for an article proving wrong an established result in theoretical physics. Her article has received zero citations.

Compare this with this article in which some other exotic idea was proven not to work. Published in Phys. Rev. Lett. and 41 citations, (b.t.w., the number of citations as the article on faster than light signals). Count Iblis (talk) 03:44, 17 October 2009 (UTC)

I'm not going to try to judge the relative validity of these sources; but I need to hear from someone who can support your interpretation before I'll be able to accept that what you wrote is verifiable. Dicklyon (talk) 03:52, 17 October 2009 (UTC)

(deindent) This effect does not allow transmitting signals faster than light. There are well known proofs that this is impossible in quantum electrodynamics with any dielectric medium made out of known charged particles. To allow signals to go faster than light requires gross violations of special relativity. I read the paper on the effect only inattentively when it came out.Likebox (talk) 16:48, 18 October 2009 (UTC)

Mentioning the definition of the metre in the first paragraph

The first sentence of the article used to read: "Its value is 299,792,458 metres per second (see the table on the right for conversions)." Wdl1961 changed it to: "The value of the meter is defined so that the speed of light is exactly 299,792,458 metres per second (see the table on the right for conversions)." Now, my personal view is that it is unnecessary to give the definition of the metre this early, because this is not the article about the metre, and this point is clearly explained just two paragraphs later. Anyway, I compromised to: "Its value is 299,792,458 metres per second (see the table on the right for conversions); this value is exact due to the definition of the metre." This avoids making the metre the subject of the sentence while giving the same piece of information. Wdl1961 essentially reverted that, with some minor wording changes. Now, I'm not willing to enter an edit war so I'm not going to revert that back myself; but I still think it is quite weird to have a sentence which sounds like we're talking about the metre, rather than about the speed of light. What do you others think? ___A. di M. 22:02, 18 October 2009 (UTC)

"Its value is 299,792,458 metres per second" this reads to me like it defines the speed of light , i will not start an stupid edit war but i would like to see the wording so it is readily apparent the speed of light is independent of the meter , which has no natural significnace anyway. i am sure there are lots of people who can word it better than what is has been and is now. my impression is lots of people ae gunshy with the page after page of nothing.Wdl1961 (talk) 22:40, 18 October 2009 (UTC)

I disagree with the recent changes and with Wdl1961's comment. Previously, the first sentence defined the speed of light (it still does). Then, the lead gave its value in SI units (the most universal standard) and referred to the box for values in other units. Definition, then value(s), puts first things first, which is what a lead should do. Later in the lead, the basis of the SI value was explained in terms of the metre's definition, which has been stable for 26 years (that is, it isn't news). That is where belongs. The current second sentence, "The metre is defined in terms of the speed of light so that the speed of light is exactly 299,792,458 metres per second", appears to be out of place, and is not likely to help the typical reader who wants to learn about the speed of light. In fact, it is meaningless to anyone who does not already know what it is talking about; that is the opposite of what a lead should do. This sentence is also redundant because asserts, cryptically, matter is explained later in the lead, where it make sense in historical context (and is explained further in the article's body, where further explanation belongs). Please look at other encyclopedic articles on the speed of light to compare how they treat this material. Also, we need edit the lead with a view to its structure as a whole; sentence-by-sentence editing, without regard to the lead's overall structure, just makes things worse. Finell (Talk) 00:22, 19 October 2009 (UTC)

I restored the second sentence as it was. Finell (Talk) 00:45, 19 October 2009 (UTC)

the second sentence determines the speed of light as a function of the meter. it says what is says. now we have to read more for a foggy explanation and inference. it would be better not to mention the meter at all in the first paragraph as the speed of light has been around for a few billions of years before the meter and napoleon.Wdl1961 (talk) 01:26, 19 October 2009 (UTC)

While I agree with Finell that the old version was better than your change, I also have sympathy for your new suggestion of just leaving the value out of the lead paragraph; previously I supported opening with the approximate value 3x10^8 as many physics books do. But this is a good time to let things settle, as we have an ongoing arbitration to finish, and then we'll be able to have a sensible discussion, I suspect. Dicklyon (talk) 01:31, 19 October 2009 (UTC)

Yes, let's by all means reach consensus on the lead rather than tinkering with aspects that are controversial. However, some positive, non-controversial improvements have been made, and some that have reduced controversy. I also agree that we should wait until the arbitration ends. Martin has urged that as well. Finell (Talk) 04:24, 19 October 2009 (UTC)

I agree with A. di M. There are two issues here:

1. The first paragraph of the lead needs to contain the value of c in SI units. There will be a significant portion of visitors to this article that are just looking for that value and nothing else. These need to be catered to by providing the value in the first paragraph AND in the infobox. These user are not interested in how the metre is defined etc.
2. There is no need to comment at that time about the value being exact because of the definition of the metre. Any mention in the fist paragraph is going to amount to some kind of cryptic statement without further qualification that is essentially meaningless to anybody not already aware of the issue. The issue is comment on only two paragraphs later where there is much more room to provide the right context.

(TimothyRias (talk) 07:54, 19 October 2009 (UTC))

Revisiting the lead and its first paragraph

There's a problem in many articles that the lead paragraph is much too complex for the average reader. The lead needs to be *simple*. The fist sentence needs also to be as simple as possible. Complications can be built upon and explained later in the lead or later in the article. The duality of SoL (i: it's a defined constant, ii: it's actually something that can be measured) circular reference thing ('an X is defined as how far Y travels in one second, thus you can't sensibly measure Y using Xs') can (and probably should) go in the lead, but most certainly not in the first sentence. NotAnIP83:149:66:11 (talk) 10:27, 19 October 2009 (UTC)

it just bothers me the second sentence is logically incorrect in stating the dependent and independent /variable reality. i have noticed through the years that english speaking people are more abstract in language use. so it is mostly my problem. sol just will not care. sofar i find the discussion interesting . Wdl1961 (talk) 13:24, 19 October 2009 (UTC)

I'm going to be half-bold, and suggest a whole new first paragraph here!

The speed of light (denoted by c or c₀) is a constant which appears in many areas of physics. It is equal to 299,792,458 metres per second (about 671 million miles per hour). It is the speed at which electromagnetic radiation (such as light) travels in vacuum, but also the maximum speed that any matter or information can travel, the constant that relates mass and energy (through the famous equation E = mc²) and that connects our measurements of length and time in the unified structure of spacetime.

— Physchim62 (talk) 14:05, 19 October 2009 (UTC)

Delete the ref to "matter", but retain ref to "information", because of the Scharnhorst effect.--Michael C. Price ^talk 14:15, 19 October 2009 (UTC)

I don't think we have to worry about the Scharnhorst effet in the first paragraph of the lead: it is currently unobservable, and may well be fundamentally unobservable. It doesn't bother the readers of the first paragraph, let's leave it at that. Physchim62 (talk) 17:15, 19 October 2009 (UTC)

I agree with Physchim62 that Scharnhorst is too esoteric for the lead. Finell (Talk) 18:53, 19 October 2009 (UTC)

Agree with Physchim62 and Finell. If it really bothers you, just say "can normally travel" rather than "can travel"; but it doesn't really bother me. ___A. di M. 19:01, 19 October 2009 (UTC)

I added a heading because we are going beyond just treatment of the metre in the first paragraph. I still believe we should let this sit for awhile, until the arbitration is over, and then take some real time overhauling the entire lead. Further, I suggest devoting a talk sub-page to hammering out the entire lead in an organized fashion (what content to include and exclude, then the paragraph structure), and giving ourselves a minimum of 2 weeks to hash it all out. Martin should also be heard on this; I believe that he is staying away from this until after the arb decision. His stated view is that we should overhaul the entire article first, then rewrite the lead as a summary of the article. I do not agree with that at present, but I do think that we should hear him out and then decide how to proceed.

Turning to the specifics (which I would rather not do now), I agree with TimothyRias' and A. di M.'s two points as summarized at the end of the (now) previous section, and with NotAnIP's remark. However, in my opinion, Physchim62's proposal goes a bit too far in the direction of brevity. Overall, I prefer the more-or-less stable version of the past 2 or 3 weeks, and would rather discuss specific revisions starting from that as the model.

Comments on Physchim62's proposed paragraph: Consistent with usual formatting for the lead, the first sentence should begin with "In physics", and delete "which appears in many areas of physics". It is important to say "physical constant", not just "constant" (it isn't the same kind of constant as pi). The c₀ notation doesn't belong in the lead, in my opinion. Whether to mention free space is an issue to decide. Since this article is Speed of light, I would say "... speed at which light and all other electromagnetic radiation ..."; I would not relegate the article's named topic to a parenthetical. Physchim62's third sentence should end with vacuum"; what follows is a different idea, and therefore a separate sentence. Sorry to sound like the pedant that I am.

Again, I would prefer to defer this discussion for awhile, then discuss content and organization of the whole lead, not just the first paragraph in isolation, before rewriting anything. Meanwhile, non-controversial tweaking of the lead through normal editing is OK with me (for whatever that is worth) unless it becomes controversial, in which case the controversial bits should be left as they are for now. Finell (Talk) 18:55, 19 October 2009 (UTC)

Martin is actually right on that point per WP:LEAD. The lead should reflect the content of the article. As such, if any major changes are to be made to the main body of the article, it is better to wait with hammering out the fine points of the lead until the rest of the content is more or less fixed. The currently is not disastrously bad. It can surely be improved upon, but there is no urgency there. (TimothyRias (talk) 19:34, 19 October 2009 (UTC))

I'm happy with what's said above. Let's get decent content into the article, and then the lead will (almost) write itself! Physchim62 (talk) 22:07, 19 October 2009 (UTC)

WP:V, WP:RS, and WP:NPOV

My recent reverts, discussed in the sections above, are not based on any point of view on the topic, but on the idea that in an article as contentious as this one, it is important not to make assertions that are not verifiable in a reliable sources, and that questionable assertions be accompanied by something about the alternative point of view on them. Otherwise, what basis do we have for driving to any kind of convergence and improvement if people just keep adding their favorite tangents and whatever logical extrapolations come to mind? I have no objection to the concepts presented in the edits I reversed; but they need decent support in sources. Dicklyon (talk) 03:33, 17 October 2009 (UTC)

The article is not that contentious at all. You have to look at what the articles are actually saying, also in what journals they are published, if they are cited a lot etc. etc. Count Iblis (talk) 03:46, 17 October 2009 (UTC)

The contentiousness tends to be among editors of speed of light; that's why we need a solid policy-based process here. Dicklyon (talk) 03:49, 17 October 2009 (UTC)

I would suggest everyone to take the time to actually read the articles. E.g. what does Heidi in her article (http://arxiv.org/abs/0706.0553 ) actually say? After she makes her claims that some nontrivial assumptions were made that she claims may not be valid (without proving that they are not valid) what does she say on page 4 about the opinion of other people with whom she discussed this at a conference? Count Iblis (talk) 04:00, 17 October 2009 (UTC)

My worries about the inclusion of this material are more that it is being given WP:UNDUE weight than anything else. The Scharnhorst effect is verifiably the subject of discussion and theoretical study in physics. It is also ludicrously small, one part in 10³⁶ for plates separated by 1 µm. It has never been measured, and one is quite justified in asking if it ever could be measured: in fact, Milonni & Svosil (1990) have claimed that the Heisenberg uncertainty in any measured velocity of propagation "will always be enormously larger than the correction to c associated with the Scharnhorst effect," in other words, the Scharnhorst effect can never be measured (as quoted in Prof. Fearn's article, can't bring myself to call her Heidi, I've never met the lady).

So, should we be saying that the Scharnhorst effect is a "known effect allowing information or energy to travel faster than c," as Count Iblis would like? I would prefer that we didn't do so on this article, although I wouldn't object to a more thorough discussion on the page devoted to the Scharnhorst effect. Should we be saying that "it is impossible for information or matter to travel faster than c," as states the version of the article that Dicklyon is reverting to? I can see Count Iblis' problem with this statement. I would be tempted to add a "measurably" in there somewhere, but it wouldn't really resolve things. Suggestions for a new wording? Physchim62 (talk) 12:29, 17 October 2009 (UTC)

Such as this one? (As far as I'm concerned, the parenthesis might as well go away: the "normally" makes the first sentence not false even if the Sch. effect were true, and the "it is thought" makes the sentence in parentheses not false even if the Sch. effect were false.) --___A. di M. 14:02, 17 October 2009 (UTC)

Yes, that's also a good solution. I'm ok. with this edit. Count Iblis (talk) 14:18, 17 October 2009 (UTC)

ec:

We could also have a more neutral statement, saying that faster than light propagation of information is problematic because it leads in general to causality violations, and then we can give a footnote in which we say that the Scharnhorst effect is a posible exception to this rule, i.e. that in this case you have faster than light propagation of information but without the possibility of using it to create a causal paradox.

About measurability, that's approached from a practial point of view in http://arxiv.org/abs/0706.0553 The article says that in so many words. The uncertainty in the velocity being much larger than the effect does not imply that you cannot see the effect in principle. It means that you would need to perform such a huge number measurements to average out that huge uncertainty that in practice you could never do that on any reasonable time scale. Count Iblis (talk) 14:15, 17 October 2009 (UTC)

The paradox is resolved by showing that even if FTL matter exists (e.g. tachyons or casimir effect photons) they can't be used to transmit FTL information. FTL energy, yes; FTL information, no. I know this sounds nonsensical, but see Gerald Feinberg's mainstream citations at the tachyon article. So the Scharnhorst effect allows FTL photons without allowing FTL information transfer or causality violations, which is what Visser et al show. Visser's work is essentially an extension of Feinberg's SR/QFT work into the domain of GR.--Michael C. Price ^talk 10:18, 19 October 2009 (UTC)

Hmmm, I thought that perpendicular to the plates you do get faster than c propagation of information but you then cannot use it to create a closed timelike loop. At least that is what I read in section 3.2 of this article (page 13 and furhter). Count Iblis (talk) 14:38, 19 October 2009 (UTC)

They (Visser et al) say that the photons move FTL, but information is not mentioned. Hawking's chronology protection conjecture is invoked to save causality, which is compatible with Feinberg.--Michael C. Price ^talk 15:06, 19 October 2009 (UTC)

Yes, but while they can use the analogous result from GR (due to the structure of the effective metric given in Eq. 3.4), in this case you do have faster than c signals. That's very clear from the proof they give that does not invoke this result. See page 16, just before the start of section 3.2.2 where they say that it is because the speed of light has a unique value for each observer with some four-velocity. It is then the fact that to violate causality you need the same larger than c signal speed in two different frames that saves causality.

Eq. 3.4. is only the effective metric, the ordinary Lorentz metric still defines speeds. Count Iblis (talk) 15:38, 19 October 2009 (UTC)

You're right, perhaps signals travel FTL as well as photons. I think all the SoL article has to do is link to chronology protection conjecture (something that it does not do at the moment), where it can be explored in more detail.--Michael C. Price ^talk 21:41, 21 October 2009 (UTC)

Signals would only travel FTL between the plates, where causality is well behaved. You would only get a problem if you could detect the FTL signal outside the plates, and uncertainty seems to cloak the system in such a way that you could never actually measure an FTL signal. Consider this extract from page 17 of Visser's paper: "The problem in this case is edge effects: the effective metric given in (3.4) is only expected to be a good approximation far away from the edge of the plates, while well outside the plates the effective metric should approach that of Minkowski space. Near the edge of the plates the effective metric is impossible to calculate, and the situation only gets worse when two pairs of half-infinite plates pass each other with a grazing not-quite collision. It is certainly clear that the simple naive result of equation (3.14) should not be trusted. The present arguments do not guarantee the total absence of causality violations, but they do demonstrate that the most naive estimates of the causality violating regime are likely to be grossly misleading." Physchim62 (talk) 08:25, 22 October 2009 (UTC)

For the record

Wikipedia:Arbitration/Requests/Case/Speed of light#Final decision

This arbitration case has been closed, and the final decision may be viewed at the link above.

• All editors are reminded to be civil at all times and seek consensus where possible, and encouraged pursue dispute resolution when necessary.
• Brews ohare (talk · contribs) is warned for his conduct in this dispute, and placed under a general probation for one year, under which any uninvolved administrator may impose sanctions if Brews ohare fails to adhere to the purpose of Wikipedia or general editing and behavioral guidelines, policies, and expectations, despite warnings.
• David Tombe (talk · contribs) is also warned for his conduct in this dispute and during the course of the arbitration case, and is placed under the same general probation but for an indefinite duration. David Tombe may not appeal his probation for one year, and is limited to one appeal every six months thereafter.
• Both Brews ohare and David Tombe are banned from all physics-related pages and topics, broadly construed, for twelve months.
• Violations of the topic bans or general sanctions may be enforced by blocks of up to a week in length for repeated violations, to increase to one year after the third block. All blocks and other sanctions applied should be logged on the case page here.

They're not my words above, but I thought they might be of use or interest to editors at this page. Physchim62 (talk) 23:58, 20 October 2009 (UTC)

To clarify, the above is the Clerk's summary of the remedies, only. The entire decision is recommended reading for editors of this page. Finell (Talk) 00:45, 21 October 2009 (UTC)

Now the dust has settled

After the excitement and stress of the arbitration it is now time to get back to improving the article. I found it hard to know where and how to start.

Previously, because of the bad feeling that abounded, it was important to discuss things on the talk page before making significant changes. Now that a general assumption of good faith has returned (I hope) it should be possible to return to normal cooperative editing in the best traditions of WP.

I have started the ball rolling with some editing to the 'Light as EM radiation' section. This is not an attempt to make any kind of point or to dominate the article and I think it still need plenty of improvement to that section is needed. I look forward to trying to get this article back to an FA by working together to improve it. Martin Hogbin (talk) 10:18, 24 October 2009 (UTC)

I've already nominated the article for peer review. (There's a link at the top of this talk page.) ___A. di M. 11:05, 24 October 2009 (UTC)

I think that the article should be looked at as a whole, rather than as edits to individual sections. The basic question is: what should we be discussing, given that we can't hope to discuss everything? Several editors have already given their opinion in the various userspace pages that cropped up (and also here, for specific points): maybe we could attempt a synthesis here. Physchim62 (talk) 13:33, 24 October 2009 (UTC)

Perhaps you could start by listing the issues that you consider important. Martin Hogbin (talk) 15:44, 24 October 2009 (UTC)

I think the article as it is now is all in all pretty good, So I don't think an "incremental" approach, in which we start from what we already have and tweak it, is that bad. (Is that what you meant by "as edits to individual sections"?) ___A. di M. 10:20, 25 October 2009 (UTC)

Yes, the article is in standard shape, so let's just treat it like any other article in such. Let's make a mod here, a mod there, an add here, an add there, a rem here, a rem there...

That should give no problem, as Hare and Tombe are no longer here to make standard wiki life impossible. DVdm (talk) 10:39, 25 October 2009 (UTC)

Astronomical units per day

I had removed the infobox expression of light speed in astronomical units per day because (1) I think it's a rather silly measure (i.e. why don't we also take parsecs per week?), and (2) it was listed in high precision, as opposed to the 3/4 digit precision of the other expressions. Physchim62 seems to have "ordered" this expression and reverted my removal, suggesting discussion on talk page. So here we are. Any thoughs? DVdm (talk) 14:16, 24 October 2009 (UTC)

Re (2) why didn't you just round it off then? --Michael C. Price ^talk 14:55, 24 October 2009 (UTC)

I had rounded it (to zero precision) to accomodate (1) and (2) at the same time :-) DVdm (talk) 15:04, 24 October 2009 (UTC)

It's no "sillier" a measure than natural units, and it is a measured value known to high precision (as opposed to the others, which have defined values). Physchim62 (talk) 10:54, 25 October 2009 (UTC)

I tend to think that 'Astronomical units per day' should stay. I can see why people are concerned, it may encourage some to add all sorts of weird units just for the sake of it. However, as I understand it, these units are not based on SI units and thus the speed of light does not have a defined value in that system of units (not that I want to revisit that argument). Martin Hogbin (talk) 12:12, 25 October 2009 (UTC)

Why not just respect policy, and include only those values and units that we can back up with a reliable source? Why should we convert to odd units of our own that don't appear in sources? By that criterion, astronmical units per day is OK (per this 1976 proceedings). Dicklyon (talk) 20:08, 25 October 2009 (UTC)

"speed+of+light"+"furlongs+per+fortnight"+-wikipedia Er... ___A. di M. 20:25, 25 October 2009 (UTC)

Yes, absolutely. And let's use Googlebooks. It's more than properly sourced. Let's take it. Why not? Because it could make someone smile? DVdm (talk) 21:43, 25 October 2009 (UTC)

Hard to say who is serious and who is not, but I agree that there's nothing wrong with quoting the value in furlongs per fortnight, a commonly used humorous unit for the speed of light. Also, let's put a book link on each value, and limit ourself to books, as opposed to random web sources and such, OK? Dicklyon (talk) 21:52, 25 October 2009 (UTC)

I don't think we need a source for each value. Having seen one for au/day, I'm already satisfied. I'd only provide one (or two) for the furlongs, sort of to "scare off" the really serious ones. DVdm (talk) 22:10, 25 October 2009 (UTC)

Selected astronomical constants in the current Astronomical Almanac gives the speed of light to a few more digits than that given in the IAU (1976) Proceedings, to wit: 1/τ_A = 173.1446326847 AU/d. The units AU/d are natural in astronomy because its fundamental measurement units are the astronomical unit, the day, and the mass of the Sun; not the metre, second and kilogram. — Joe Kress (talk) 05:36, 26 October 2009 (UTC)

I would prefer to give this in Au/hour. You get a smaller number; the time scale of hours is more relevant when thinking about communicating with spacecraft in the solar system. Also, if we use Au/day, then "day" has to be defined, there is more than one definition in astronomy. Count Iblis (talk) 17:47, 26 October 2009 (UTC)

We have a source using au/day. Do you have one using au/hour? DVdm (talk) 17:51, 26 October 2009 (UTC)

And you don't have that same problem with hour? In astronomy that is usually 1/24th day.(be it solar,siderial or SI). Let's stay with what the sources are using au/day.(TimothyRias (talk) 09:42, 27 October 2009 (UTC))

The value I put in is for a day of 86,400 TDB seconds, that is for the mean day measured as 86,400 seconds on the surface of the geoid. You do get slightly different values if you use different time scales, as there is no absolute consensus as to how to account for gravitational time dilation in astronomical measurements and the SI system is fairly silent on the matter. The TDB value (the one I put in the infobox) is the one that's used practically. Physchim62 (talk) 15:02, 27 October 2009 (UTC)

Modern astronomical units

I have removed this part of the above section because it is unreferenced and because it makes no mention of the uncertainty units or, failing units, a ratio? Surely a bald number mean nothing in this context?

"The relative uncertainty in these measurements is 2 × 10−11, equivalent to the uncertainty in Earth-based measurements of length by interferometry." Abtract (talk) 17:21, 26 October 2009 (UTC)

Relative uncertainty is dimensionless. See for instance here. Want more? Here's some more. DVdm (talk) 17:39, 26 October 2009 (UTC)

Thanks that was very useful. I have two points to make: 1) It would be better written as 20 parts per trillion as one of your sources suggests (per million actually but ...) as this would make it clear to simpletons like me that it was per something. 2) It is uncited and atm is original research even though it is a simple calculation. Abtract (talk) 18:32, 26 October 2009 (UTC)

You are welcome. Concerning your remarks "...simpletons like me..." and "...original research even though it is a simple calculation.", perhaps this is useful as well: "...Any relatively simple and direct mathematical calculation that reasonably educated readers can be expected to quickly and easily reproduce...". :-) DVdm (talk) 18:42, 26 October 2009 (UTC)

Thanks again ... I will be sooooo knowledeable soon. Abtract (talk) 18:50, 26 October 2009 (UTC)

No problem. I have removed the fact-tag, and got rid of the treacherously ambiguous trillions as well. - DVdm (talk) 19:01, 26 October 2009 (UTC)

Actually, nowadays the "short scale" is the only one used in modern English, even in countries where the long scale was formerly used. This article itself is written in British English but consistently uses "billion" to mean 10⁹. Anyway, the trillion is much less familiar than the billion, so I vote for "2×10⁻¹¹" (or for "0.02 parts per billion"). ___A. di M. 19:45, 26 October 2009 (UTC)

Obviously anything larger than "million" should not be used for any article used worldwide.Wdl1961 (talk) 20:46, 26 October 2009 (UTC)

C'mon, even the BBC by billion now mean 10⁹ (and by now I mean "for the last couple of decades at least")... ___A. di M. 20:54, 26 October 2009 (UTC)

what's BBC ? There are other areas than gob and even places where english is not spoken. I know i have been there. By the way billion equals million x million. Milliard equals thousand million.Wdl1961 (talk) 21:16, 26 October 2009 (UTC)

That is generally regarded as outdated even in the UK. When I was at school a billion was unambiguously 10⁹ and that was 15 years ago. In any case we have an official policy on the topic (see WP:ORDINAL) which says which approach should be taken. CrispMuncher (talk) 21:27, 26 October 2009 (UTC)

Huh? This article is written in English, so what do places where English is not spoken have to do with this? ___A. di M. 21:44, 26 October 2009 (UTC)

I tend to agree with Wdl1961 on this. Anything beyond "million" invariably makes at least some readers wonder. Whenever we can avoid that, I think we should :-)

Indeed, from WP:ORDINAL#Numbers as figures or words we can use bullet_2 ("Comparable quantities should be all spelled out or all figures: we may write either 5 cats and 32 dogs or five cats and thirty-two dogs, not five cats and 32 dogs.") and bullet_11 ("Measurements, stock prices, and other quasi-continuous quantities are normally stated in figures.") DVdm (talk) 22:07, 26 October 2009 (UTC)

Yeah, and the following bullet says "When expressing large approximate quantities, it is preferable to write them spelled out, or partly in figures and part as a spelled‑out named number". "13,000,000,000 years" looks like it has eleven significant figures and is slightly less "immediate" to read; maybe "1.3×10¹⁰ years", but I think that the intended readership of the article includes people unfamiliar with scientific notation. As for the countries using long scale, none of them is English-speaking, so it's no more confusing than "actually", whose cognate in most other European languages means "now". ___A. di M. 22:19, 26 October 2009 (UTC)

May i suggest 13 billion (13×10⁹) years. Wdl1961 (talk) 23:45, 26 October 2009 (UTC)

Ah... Whatever Works, right? :-) DVdm (talk) 09:41, 27 October 2009 (UTC)

Wdl1961's suggestion below is what works best, IMO. (I didn't apply it when "billion" was used several times in the same section because I expect their attention span to be longer than they take to read it, and that they be able to figure out that no-one'd use "billion" with two different meanings in the same section unless explicitly discussing these meanings. ___A. di M. 09:53, 27 October 2009 (UTC)

I find it ironic that we can go from discussing the arcane depths of quantum electrodynamics (see the discussion of the Scharnhorst effect above), to suggesting that readers (who would have gotten past all the relativity in the article to reach the end) cannot understand the scientific notation of small numbers! Physchim62 (talk) 13:19, 28 October 2009 (UTC)

Even more ironic is suggesting that they cannot understand "parts per billion". And, FWIW, Abtract did fail to understand what "relative uncertainty of 2×10⁻¹¹" meant (see above). (Anyway, now that the article shows both forms, this discussion is moot.) ___A. di M. 14:19, 28 October 2009 (UTC)

Learning to use english "after getting of the boat" I was more confused or a long time , there was no wikpedia! Therefore I believe in keeping it simple to correlate quantities . I am sure the english wikpedia is used by an higher percentage non native speakers than any other language wikpedia. Wdl1961 (talk) 15:08, 28 October 2009 (UTC)

Exact in imperial units

I've added the statement, in a footnote, that:

The speed of light is exactly 186,282 miles, 698 yards, 2 feet, 5 and 21/127 of an inch per second.Physics forum

I notice that some of the threads there and elsewhere went through the exact business that we flogged to death w.r.t. metric units, so it seemed worthwhile slaying the dragon here as well: exactness is not a specific to just S.I. units. --Michael C. Price ^talk 14:21, 29 October 2009 (UTC)

If you're going to say, you better cite a source, at least one that shows that the mile is exactly defined in terms of the 1983 meter. I though we had concluded that was not the case. Not sure. Dicklyon (talk) 15:57, 29 October 2009 (UTC)

I thought that was what my source did show. I missed that earlier discussion. But since the one inch is exactly 2.54 centimetres c must have some exact imperial measure.... I would have thought.--Michael C. Price ^talk 16:30, 29 October 2009 (UTC)

See yard. By international agreement a yard is defined as exactly 0.9144 metres, irrespective of how the metre is defined. As such the yard was also redefined by inheriting the effects of the 1983 redefinition. Thus all other imperial units of length inherit a rational and exact metric equivalence. I think the current treatment is a good one - it doesn't clutter up the main article with details but makes the exact relationship clear. CrispMuncher (talk) 17:20, 29 October 2009 (UTC)

Fwiw, I have wikilinked the relevant quantities in the note. I also wanted to get rid of the pointer to physforum which as a wp:source must be about the very worst we can possibly come up with, but then there is no source in the citations section. Is there a way to created a note in a notes section at the bottom? Can we just remove the url from the ref and rename the ==Citataions== subsectoin to for instance ==Notes and Citations== ? DVdm (talk) 11:07, 30 October 2009 (UTC)

If you read Mile, you'll see why this is anything but routine and simple. The idea that the value is exact depends on a chain of deductions that applies in a number of countries, but is by no means universal. And the calculation, though "routine", is no means trivial to execute, in either direction. The average reader is neither going to understand the basis or limitations of the claimed exactness, not be able to verify the numbers. We really shouldn't be stating such strained deductions without a source, per WP:NOR. Many books talk about c being exact in SI; do any talk about it being exact in miles or yards? If so, cite; if not, omit. Dicklyon (talk) 15:39, 30 October 2009 (UTC)

I did read mile before making the note. But removal is not satisfactory; readers will think that there is something magical about the SI units, which is false. Better to just state in the note that we are using the international definitions of mile, yard etc.--Michael C. Price ^talk 15:54, 30 October 2009 (UTC)

Better to say nothing without a source. And there is something special about the SI units: that's where the distance standard is defined in terms of the speed of light; the exactness gets inherited by other systems that by treaty or whatever are tied to the SI metre, but not all miles and yards are. It's not up to us to worry to much about what readers might think when omit to say what we think; we need to stick to WP:V. Dicklyon (talk) 16:01, 30 October 2009 (UTC)

As for WP:NOR, the statement "This policy does not forbid routine calculations, such as adding numbers, converting units, or calculating a person's age, provided editors agree that the arithmetic and its application correctly reflect the information published by the sources from which it is derived" seems to depend on the calculation being simple routine, and on editors agreeing. I don't think it's simple at all, given the complexities in both the chain of inferences that would be needed to define for which mile it is true, as well as the numerical calculation. Has anyone here even bothered to try to verify the numbers from the physics forum? Was it a simple or routine calculation? Why are we getting into this without a source? Don't we have enough trouble in this article without punting on WP:V? Dicklyon (talk) 16:09, 30 October 2009 (UTC)

I verified the numbers from the physics forum. In fact I derived the numbers first and then googled the numerical values to see that the rest of the world agreed.

I've added the explanation about "international mile" (with source) to note.--Michael C. Price ^talk 16:12, 30 October 2009 (UTC)

OK, so it's your original research. Thanks for verifying that. If you want to put in something about the exactness in miles, here is a book that ties miles to meters as "exact", in the context of a discussion of the exactness of the speed of light. I think it would be best to state that the mile has this exact relation to the meter in at least some countries, but to not include your OR numbers. Dicklyon (talk) 16:16, 30 October 2009 (UTC)

My OR? So what part of "and then googled the numerical values to see that the rest of the world agreed" could you not follow?--Michael C. Price ^talk 16:22, 30 October 2009 (UTC)

I thought I had followed you when you said you did the calculation yourself, and then found it in physics forums and such but not in any reliable source. Did I misunderstand? Dicklyon (talk) 16:50, 30 October 2009 (UTC)

I propose we just add the following sentence at the end of the first section:

• Using the common official definitions of the mile (1609.344 metres), the yard (0.9144 metres), the foot (0.3048 metres) and the inch (0.0254 metres), the speed of light can expressed exactly in imperial units as 186,282 miles, 698 yards, 2 feet, 5 and 21/127 of an inch per second.

This clearly is accordance with wp:NOTOR. Everone can easily verify it and we have a source. Okay with everyone? DVdm (talk) 17:08, 30 October 2009 (UTC)

We do unit conversions all the time in Wikipedia and they are generally not considered OR. See MOS:CONVERSIONS "Generally, conversions to and from metric units and US or imperial units should be provided ... Converted values should use a level of precision similar to that of the source value ...", so giving an exact conversion seems appropriate here. On the other hand using miles, yards, feet and inches seems unnecessarily dramatic and POV ("look how quaint the old system is"). At least get rid of yards.--agr (talk) 17:14, 30 October 2009 (UTC)

Remove the yards if you like. --Michael C. Price ^talk 17:32, 30 October 2009 (UTC)

I have an alternative proposal:

• In countries that define the inch as exactly 2.54 cm, the mile is exactly 1609.344 metres, so the value of c in miles per second is also exact; the value can not be expressed as a terminating decimal fraction however, so would need to be expressed with fractions or a repeating decimal to be exact.

The difference is that in my version, the cited source supports the text it is attached to, and we omit the unsourced OR that Michael Price did. Dicklyon (talk) 17:25, 30 October 2009 (UTC)

For nth time, routine calculations do not require sourcing. And it looks rather odd to say that the speed of light can be expressed exactly and then not give it. And where is the sourcing for "the value can not be expressed as a terminating decimal fraction however, so would need to be expressed with fractions or a repeating decimal to be exact" which your pedantry requires? --Michael C. Price ^talk 17:32, 30 October 2009 (UTC)

Response to Arnold's DVdm's proposal : I would prefer if this was footnoted rather than in the main text, and especially not in the lead section. This is essentially a side note and should not clutter up the rest of the article. I suspect few are ultimately that bothered about an exact Imperial value and it does not have the same kind of importance as the metric value which is exact by definition rather than indirectly by several equivalences.

To address Dicklyon's comments, this is not a matter of a simple units conversion: it is more assertive than that. Saying that a value is exact is much more forceful than simply giving an aprroximation in other units. It is only natural than beign so uncategorical needs much more justification than a normal approximation. CrispMuncher (talk) 17:31, 30 October 2009 (UTC)

If we're going to do a units conversion and call it routine, we should pick the units. Say miles. Then express the exact number as an integer plus fraction number of miles. This mixed units stuff is crazy. But if we're doing that for miles per second, what about all the others units? Will we be putting similar notes on miles per hour, km / sec, etc.? The note about not being able to give the digits was intended as an explanation of why we don't just give the digits like we do for meters; it's about as much OR as the converted value, but at least I didn't pretend it's sourced.

In general, I synpathize more with CrispMuncher's concern that we not clutter up the lead with irrelevant trivia; but burying irrelevant trivia, esp. unsourced OR trivia, in footnotes is also not so good. I think I've been consistent in pushing back on such things in many articles. Dicklyon (talk) 17:53, 30 October 2009 (UTC)

Miles per second is more notable than miles per hour or furlongs per week -- it's the one I and millions of others were taught in school.

The "mixed stuff" is not "crazy" -- that's how the imperial system works, remember? And that's how it was expressed at the source.

To avoid cluttering up the lead we can place the text elsewhere. But of course a footnote doesn't clutter up anything.--Michael C. Price ^talk 18:05, 30 October 2009 (UTC)

I stick with my original proposal. It is just one sentence, it is easily verified, it uses all the quantities to be found in the wiki, and i.m.o. it does not qualify as a mere trivium ( - look at the length of and the number of contributors to this section and the physforum thread - people seem to be interested in this - ). I think it is a mildly interesting little fact, to be listed at the end of the values section. DVdm (talk) 18:11, 30 October 2009 (UTC)

Agreed, end of the values section looks a sensible place. End of the 1st paragraph looks a good place. Added it. See what you think. --Michael C. Price ^talk 18:19, 30 October 2009 (UTC)

I had the very end of the section in mind, but end of paragraph is even better. DVdm (talk) 21:23, 30 October 2009 (UTC)

New results on frequency consistency

The New York Times is reporting new results on frequency consistency of c based on observation of gamma ray bursts [1] that set limits on any possible quantum gravity effect. --agr (talk) 19:30, 29 October 2009 (UTC)

Definitely seems to be worth a mention. Dicklyon (talk) 06:30, 5 November 2009 (UTC)

In vacuum

I notice the odd phrase "speed of light in vacuum" appears repeatedly; shouldn't it be "speed of light in the vacuum". I'm guessing that this is an artifact of the "free space" vs "vacuum" war? --Michael C. Price ^talk 00:00, 31 October 2009 (UTC)

the "in vacuum" is already implicit in "speed of light" after the definition in the lead, so probably should just omit it, unless specifically comparing to non-vacuum. I don't know about "the". Dicklyon (talk) 00:11, 31 October 2009 (UTC)

Well, normally one would say "in water" rather than "in the water". But Love Is in the Air... The English language is weird. Anyway, http://www.googlefight.com/index.php?lang=en_GB&word1=%22in+vacuum%22&word2=%22in+the+vacuum%22. ___A. di M. 11:03, 31 October 2009 (UTC)

We can also write "the speed of the light in the vacuum". Then it will look like the page has been edited by a Russian editor. Count Iblis (talk) 14:55, 31 October 2009 (UTC)

Perhaps the way to settle this is by referring to an authoritative reliable source, like http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf , which uses "speed of light in vacuum". --Bob K31416 (talk) 04:30, 5 November 2009 (UTC)

General notes

First sentence: "electromagnetic radiation, such as *visible* light..."

"Light" can both mean EM radiation and visible light, when used in a sentence that already contains the term EM radiation it is clear that the latter meaning is meant. Adding "visible" would feel a tad pedantic to me. (TimothyRias (talk) 15:59, 27 October 2009 (UTC))

The problem is the whole sentence "the speed of light refers to the speed of EM radation such as light." "visible light" reads better. I would add some more examples to make it less "well duh". Something like "and is the speed at which electromagnetic radiation, such as radio waves or visible light, travels in vacuum." Headbomb {^ταλκ_{κοντριβς} – WP Physics} 16:59, 9 November 2009 (UTC)

Third paragraph: the physical meter rod was no longer used in the early 1960's. At that time ("1975" as stated), a large-but-finite number of wavelengths of characteristic radiation were used to define the meter, and the uncertainty derived from the uncertainty in the wavelengths... the meter itself was not uncertain.

Actually, I think there was an uncertainty in what exact wavelength was to be used to define light making the definition of the metre in it self fuzzy. (TimothyRias (talk) 15:59, 27 October 2009 (UTC))

Fourth paragraph: the speed of light of X-rays an gamma radiation in air is c. More energetic radiation does not "propagate" so much as "penetrate". The "index of refraction" is wavelength dependent, and the values / ranges cited apply to *visible* light.

This paragraph could indeed use some improvement. (TimothyRias (talk) 15:59, 27 October 2009 (UTC))

Section "The nature of light", subsection "Light as photons", a nod to the photoelectric effect would be a really good idea here.

In what sense? Please by bold if you have a specific idea. (TimothyRias (talk) 15:59, 27 October 2009 (UTC))

The photoelectric effect was what suggested Einstein that light might be discrete. (Planck did that before, but he considered that to be just a mathematical trick, with no direct physical significance.) So if we needed to have a one-paragraph explanation of the history of QED in "Light as photons", the photoelectric effect would have to be mentioned; but I think the current content of that section is sufficient for the scope of this article. ___A. di M. 21:33, 27 October 2009 (UTC)

Personally, I think it would be a mistake to mix up photons with speed of light. Light propagates as a wave, which has a speed; the quantized or particle aspect has not so much to do with the propagation or the speed; we speak of photons traveling at the speed of light, but that really is mixup of the wave/particle properties. QED is all about the waves, leading to event probabilities. Dicklyon (talk) 23:35, 27 October 2009 (UTC)

Section "Fundamental importance in physics", subsection "Variations with time and frequency", a massive photon will violate charge conservation, and the mass is not "taken to be zero", but its rest mass has been experimentally verified to be 18 orders of magnitude smaller than its energy... inclusive of zero.

In (almost) any calculation the value for the photon mass *is* taken to be zero. i.e. Zero is used as the preferred value consistent with experimental bounds. (TimothyRias (talk) 15:59, 27 October 2009 (UTC))

Section "History", subsection "Redefinition of the meter", the 1972 values established c as 299792462 (Bay/Luther/White) or 299792460 (NRC/NBS), with less accuracy than established by the US-NBS in 1983. The US-NBS value of 299792458.6 in 1983 was truncated, and carried a smaller uncertainty. 98.165.4.177 (talk) 02:16, 27 October 2009 (UTC) David A. Smith

Reply from David A. Smith (transplanted from User_talk:TimothyRias)

This is David A. Smith from a different IP address.

Re: third paragraph. There was no uncertainty in which wavelength of light was to be used for measuring c between early 1960s and 1983. One wavelength was chosen, and then another (shorter) was chosen later as being better because it was sharper. But wavelengths do not derive from classical equations, and mapping from quantum processes to the macroscopic world leaves uncertainty.

Re: Section "The nature of light", subsection "Light as photons" Peer review implies that the text is controlled in some sense, to be edited by others. So my 'bold' contribution might be to add this sentence: The [photoelectric effect] shows that light is comprised of discrete packets of energy, that do not merge to fewer, more energetic, packets as waves would.

Re: Section "Fundamental importance in physics", subsection "Variations with time and frequency" What is made is a blanket statement, implying that we did not look for the mass of a photon. We did. I suggest that if the wording stays as is, it is preceded by a statement referring to experimental testing of a photon's rest mass.

David A. Smith 216.161.188.207 (talk) 16:32, 27 October 2009 (UTC)

meter

Speed of light is what it is and the meter in Paris is what it is. The problem was that the speed of light could be measured more accurately than the meter. Therefore meter = k x Speed of light , not the reverse. Wdl1961 (talk) 00:38, 31 October 2009 (UTC)

Divide both sides by k and use the reflexive property of equality. It cannot be the case that A equals B but B does not equal A. ___A. di M. 16:40, 4 November 2009 (UTC)

It is not a math problem but logic / language use item and the definition. Stating a implies b is not the same as b implies a. an human is a mammal does not imply that a mammal is human. It does not look good in the second sentence of the article.Wdl1961 (talk) 04:02, 5 November 2009 (UTC)

It's not clear to me what change you are proposing. Dicklyon (talk) 06:29, 5 November 2009 (UTC)

I tried "The value of the meter is defined so that the speed of light is exactly 299,792,458 metres per second" before. In my opion "The meter is defined ----- " is essential at the start of the article . Wdl1961 (talk) 15:09, 5 November 2009 (UTC)

Why is it essential at the start? Imho the definition of the metre is little more than a footnote in an article about the speed of light. Indeed the units used to specify the sol are only metres and seconds in order to aid the casual reader who surely has no interest in its exact value or how the unit of length is defined. This is/should be an article about a concept, a fundamental constant of nature ... not a foray into how SI units are defined. Abtract (talk) 16:00, 5 November 2009 (UTC)

Exactly; all this subtlety that people like to belabor is best kept out the lead. And the "value of the meter" has no obvious interpretation to me; what does "value" mean here? It usually implies a number, but the definition of the meter is about a distance in terms of time and the fundamental constant c, not about a "value". Dicklyon (talk) 16:26, 5 November 2009 (UTC)

It should be clear what is the dependent and independent variable. "sol =" is worse than "meter = ".Wdl1961 (talk) 16:11, 5 November 2009 (UTC)

Again, proposed some text and an appropriate place for it. It's not clear what "variables" you refer to here. Dicklyon (talk) 16:26, 5 November 2009 (UTC)

(edit conflict)It seems that there have been problems in discussing this article because there are subtle points that need special effort for communicating. It is important that editors understand the points made by each other. So with that in mind, may I ask you to explain in more detail what you mean by "It should be clear what is the dependent and independent variable." For example, what do you feel is the "independent variable" and why? --Bob K31416 (talk) 16:31, 5 November 2009 (UTC)

There are endless discussions in the past . No point in rehashing . Right now the sol is the ultimate and fundamental parameter not defined or dependent on anything else .This should be clear immediately.(like it or not. i still use a string in secret) Wdl1961 (talk) 16:52, 5 November 2009 (UTC)

I don't think that stating "its value is 299,792,458 m/s" suggests that it's the metre which decides how fast light goes, any more than (say) "The average centre-to-centre distance from the Earth to the Moon is 384,403 kilometres" suggests that it's the kilometre which decides how far away the Moon is. Furthermore, it is a true statement, and it is the first thing most readers will want to know. The analogy with "human" and "mammal" is broken, because "a human is a mammal" means that the set of humans is a subset of the set of mammals. But there's only one speed of light in vacuum; a better analogy would be "The current King of Spain is Juan Carlos I" and "Juan Carlos I is the current King of Spain", which have identical meanings; but of course the former would sound strange in the article Juan Carlos I, and the latter would sound strange in the article King of Spain. ___A. di M. 17:04, 5 November 2009 (UTC)

Wdl1961, In response to my question, it appears that your answer is that the speed of light is the independent variable. And I think what you mean by calling it the "independent variable" is that a characteristic of light, viz. its speed in vacuum, is something that is not set by humankind, but rather measured. If that's what you mean, that seems like a reasonable comment. Is that what you mean? --Bob K31416 (talk) 17:59, 5 November 2009 (UTC)

The speed of light is sol for at least 15 billion years. Everything else (language, logic , physics ,etc. ) are human artifacts. I am too stupid and refuse to get confused on a high level.Wdl1961 (talk) 19:04, 5 November 2009 (UTC)

Re "I am too stupid and refuse to get confused on a high level." - It seems that you don't wish to answer my last question, so I won't pursue the discussion with you. Thanks anyhow. --Bob K31416 (talk) 19:21, 5 November 2009 (UTC)

I thought sol before artifacts placed it in the proper perspective and answered the question. My only point is that "sol = whatever" is simply not in accordance with the definition. I tried two alternate statements before but i am sure that someone could do a better job .Wdl1961 (talk) 21:15, 5 November 2009 (UTC)

quote

""==Numerical value, notation and units==

The speed of light is a dimensional physical constant, so its numerical value depends upon the system of units used. In the International System of Units (SI), the metre is defined as the distance light travels in vacuum in 1⁄299792458 of a second (see "Redefinition of the metre", below). The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s.""

perfect but too long for an opening .Wdl1961 (talk) 15:29, 7 November 2009 (UTC)

One part of what you wrote, that I think you should be careful with, is your sentence: "The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s." The definition of metre fixes the value of the speed of light, not the speed of light itself, which is a physical phenomenon.

Please note that I am using the term "value", as defined by the 4th definition on the page of the dictionary here.

Definition of value - a numerical quantity that is assigned or is determined by calculation or measurement <let x take on positive values> <a value for the age of the earth>

--Bob K31416 (talk) 16:13, 7 November 2009 (UTC)

Right now i am studying the Spherical cow ,Heisenberg and a "tarpit " trying to stay away (too late?) from too much trouble.Wdl1961 (talk) 17:54, 7 November 2009 (UTC)

Sorry, I misunderstood Wdl1961's message which quoted a part of the article which he simply thought was too long. From a few of the sources I saw in this article, it appears that the sources don't make the distinction that I made above between "value of the speed of light" and "speed of light", so I'll withdraw the above remarks of mine. --Bob K31416 (talk) 00:36, 8 November 2009 (UTC)

Proposal for the second sentence in the article:

The meter is defined so that light covers 299792458 meter in one second.

Wdl1961 (talk) 03:03, 8 November 2009 (UTC)

This statement would appear to the reader to be more about the metre than the speed of light, and hence misplaced. The present sentence seems more appropriate: "Its value is 299,792,458 metres per second." --Bob K31416 (talk) 03:24, 8 November 2009 (UTC)

That proposal has been rejected by concensus so many times it makes my head hurt. There is a quite general concensus to not mention the meter defined in terms of the distance travelled by light in the opening paragraph simply because it is not that important. The value in meters per second DOES need to appear in the opening paragraph because it is the most familiar set of units to express the constant in worldwide. (Everybody knows approximately how fast 1 m/s is.) The whole definition business is only of tangent interest to the article. (TimothyRias (talk) 10:48, 9 November 2009 (UTC))

Title correct?

It seems that this article isn't titled correctly. It appears to be about the "speed of light in vacuum" (which is the physical constant) as opposed to the more general "speed of light", which can be in vacuum or matter. It wouldn't surprise me if this subject came up before and I would be interested in the reason why the present title was used. Thanks. --Bob K31416 (talk) 03:24, 5 November 2009 (UTC)

There are two common approaches: (1) call the constant the "speed of light" and call it c like we do here, and like these hundreds of books do; and (2) call the constant the "speed of light in vacuum" and call it c₀ to distinguish it from speeds of light in other materials, like these hundreds of books do. Neither is more correct than the other; we had to choose one; you'll open a tarpit if you attempt to get a consensus to change to the other. Dicklyon (talk) 06:28, 5 November 2009 (UTC)

Dick, I truly appreciate your response. Also, I recognize that this is the Wikipedia, and these things are decided by a consensus of anyone who chooses to participate, rather than the editorial board of a physics journal. So I will definitely heed your warning regarding the tarpit. Also, I think I'll end my brief visit here. Regards, --Bob K31416 (talk) 12:14, 5 November 2009 (UTC)

I have thought for some time that this article ought to be renamed "The speed of light c" so that discussion about the behaviour of light in various media could be hived off into diffraction or an article something like diffraction of light or light in a medium. that would enable this article to be more focussed. Abtract (talk) 16:09, 5 November 2009 (UTC)

Maybe we can have a hatnote or something stating "unless specified otherwise, the phrase speed of light in this article will refer to the speed of light in vacuum?" ___A. di M. 16:57, 5 November 2009 (UTC)

I think that type of clarification would be OK. Perhaps, we could be more specific and make the note, "In this article, for the sake of simplicity, unless the term 'speed of light' specifically refers to the speed in matter, it will mean the speed of light in vacuum." Actually, I can see why doing it that way would be preferable to changing the title of the article, since we wouldn't have to keep repeating "in vacuum". --Bob K31416 (talk) 18:16, 5 November 2009 (UTC)

Why is it preferable? Abtract (talk) 18:29, 5 November 2009 (UTC)

I thought I answered that with "that way would be preferable to changing the title of the article, since we wouldn't have to keep repeating 'in vacuum' ." Perhaps you could help out by saying what you didn't understand about this statement? --Bob K31416 (talk) 18:39, 5 November 2009 (UTC)

I'm confused too, about what Abtract meant to ask: what does he mean by "it"? Or what does Bob mean by "doing it that way"? Too elliptical for me. When we have specific proposals for hatnotes, renaming, etc., we can get more specific feedback. Personally, I think the opening sentence of the article is clear enough, and don't see why people are concerned, so I'd oppose both a move and a hatnote of the sorts being discussed. Dicklyon (talk) 19:23, 5 November 2009 (UTC)

Re "Or what does Bob mean by 'doing it that way'?" - I was referring to A. di M.'s previous remark: "Maybe we can have a hatnote or something stating 'unless specified otherwise, the phrase speed of light in this article will refer to the speed of light in vacuum'?"

I followed it up with a suggestion. And from your response, you apparently oppose these suggestions because you feel it is adequately covered already. I'm willing to leave it at that, since further discussion might reopen the tarpit that you mentioned in your first response, and I don't think the issue is sufficiently important to risk that. --Bob K31416 (talk) 19:51, 5 November 2009 (UTC)

"more precise definition" vs "better realization"

In a recent edit that was reverted, there was the following change from "better realization" to "more precise definition".[2]

Improved experimental techniques do not affect the value of the speed of light in SI units, but do result in a better realization more precise definition of the SI metre.

I was motivated to make the change because "better realization" isn't clear.

Here's why I thought the change worked: The metre is defined in terms of the speed of light. If the speed of light is more precisely known, the definition of the metre is more precise. For example, if the the speed of light was measured with an uncertainty of 10%, the meter would be defined with an uncertainty of 10%. Because of this, any measurement in terms of the metre would have at least a 10% uncertainty. In other words, the definition of the metre wouldn't be very precise. If the speed of light were measured with an uncertainty of 4 ppb, as it was in 1972, this would result in a more precise definition of the metre. And if experimental techniques in the future improved even more, and the speed of light was measured even more precisely, for example with an uncertainty 0.1 ppb, the definition of the metre would be even more precise. This is why I made the change in the text to "more precise definition". --Bob K31416 (talk) 12:34, 11 November 2009 (UTC)

The change does not work, since the definition is "the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second" - That will remain unchanged, so it cannot become a "more precise definition". It remains the same definition. DVdm (talk)

If the length of the path travelled by light is more precisely known because the speed of light is more precisely known, then the definition of the metre is more precise. It's the same definition, just more precise, as I discussed above. --Bob K31416 (talk) 12:50, 11 November 2009 (UTC)

I agree that "better realization" is vague, but the definition of the metre is not changed by a better speed of light experiment. I would suggest instead "but would allow more precise measurements of length in meters."--agr (talk) 12:59, 11 November 2009 (UTC)

(edit conflict) Not really, although I understand your [Bob's] confusion. If we had better techniques, we would have more precise measurements of length in metres. The definition of the metre wouldn't change – it is exact, well, by definition – but our ability to measure things would improve. At present, national metrology labs can measure lengths of the order of one metre to an accuracy of 0.02 ppb, which raises certain philosophical questions – we're at subatomic scale there! – but that's what they say. Astronomical measurements are of a similar level of accuracy, it's when you get to smaller scales of length that the measurement uncertainties start increasing. Physchim62 (talk) 13:05, 11 November 2009 (UTC)

Thanks for pointing out 0.02 ppb. I visited the article on the metre and found this:

For purposes of delineating the metre, the BIPM currently considers the HeNe laser wavelength to be as follows: λ_HeNe = 632.99139822 nm with an estimated relative standard uncertainty (U) of 2.5×10⁻¹¹. This uncertainty is currently the limiting factor in laboratory realisations of the metre..."

--Bob K31416 (talk) 15:40, 11 November 2009 (UTC)

"Realization" is a jargon word used in metrology. It refers to the logical difference between the definition and the precision with it can put into reality (can be realized). In understand the confusion and maybe we need to make it a little more clear, but you change was even more confusing since it made no sense on the logical level, (the definition does/can not change as result of a measurement.) (TimothyRias (talk) 13:34, 11 November 2009 (UTC))

Does anyone have any suggestions on how to make "realization" more clear or have an alternate wording? Thanks. --Bob K31416 (talk) 14:34, 11 November 2009 (UTC)

"better determination" --Michael C. Price ^talk 14:37, 11 November 2009 (UTC)

I like your use of the word "determination". How about "more precise determination"? --Bob K31416 (talk) 14:41, 11 November 2009 (UTC)

How about "measurement", as used by both myself and another editor just above? Physchim62 (talk) 14:59, 11 November 2009 (UTC)

It seems like measurements are used to determine the length of the metre. And a more precise measurement would result in a more precise determination of the metre. So it seems to me that "determination" would be better. But I'm flexible on this. --Bob K31416 (talk) 15:08, 11 November 2009 (UTC)

On second thought, if "realization" is the proper jargon, maybe we should use it and have a link to what it means in this context? --Bob K31416 (talk) 15:44, 11 November 2009 (UTC)

(edit conflict)

"Realisation" (with 's') appears 5 times in the Metrology article, so I have provided a wikilink to the first occurrence of realisation in this article. The meaning should be clear to everyone now. DVdm (talk) 15:53, 11 November 2009 (UTC)

Good effort, but the term doesn't seem to be defined in that article. Also, it may not be clear to the reader what to look for in that article, since the reader would be expecting a definition, or where to look in that article. There's another article which may be close to the definition: Realization (probability) but still may not be informative enough. --Bob K31416 (talk) 16:14, 11 November 2009 (UTC)

P.S. One possibility is to edit the Metrology article so that it includes a definition of realisation that we can link to. I just brought the subject up over there. In any case, it seems like the definition would be useful in that article. --Bob K31416 (talk) 16:30, 11 November 2009 (UTC)

I agree that "realisation" is jargon that does not help our readers understand what is going on. I would suggest "...but would allow more precise measurements of length in meters."--agr (talk) 16:24, 11 November 2009 (UTC)

"measurement" is going to sound circular to some readers.--Michael C. Price ^talk 17:06, 11 November 2009 (UTC)

How is "measurement of length" circular? Perhaps I am missing something.--agr (talk) 17:39, 11 November 2009 (UTC)

"measurement of the length of a meter" --Michael C. Price ^talk 17:45, 11 November 2009 (UTC)

There may be some miscommunication here. agr wrote "measurements of length in meters", like measuring the distance to the moon in meters. This is different from "measurement of the length of a meter", which I think Michael feels is circular because of using a meter to measure a meter. --Bob K31416 (talk) 20:30, 11 November 2009 (UTC)

As I explained in this rambling during the ArbCom time, all measurements are ultimately measurement of ratios, and their uncertainty include both that in the ratio of the thing you are measuring to the standard you're using to measure it, and that in the ratio of the standard you're using to measure and the standard used to define the unit of measurement. The more precisely you can measure the number of caesium-133 wavelengths in a stick multiplied by 299,792,458⁄9,192,631,770—which can be seen as measuring the stick in terms of the metre or the metre in terms of the stick, the more precisely you can determine how many metres you are tall by using that stick. (Of course, in the case of measurements of sticks and people, there will be muuuuuch larger uncertainties due to umpteen other factors, but you get the point.) ___A. di M. 23:37, 15 November 2009 (UTC)

I think we should stick to 'realisation'. Alternatives can suggest the wrong meaning, that is why the jargon was invented. I have also seen 'delineation' of the metre used but this is no clearer that 'realisation'. Martin Hogbin (talk) 18:00, 11 November 2009 (UTC)

It seems OK to change "better" to "more precise", so I made that edit. --Bob K31416 (talk) 18:51, 11 November 2009 (UTC)

I guess all this shows that we need an article realisation (metrology). I'm adding a red link to the article to show this. ___A. di M. 23:08, 15 November 2009 (UTC)

Perhaps it would be better to explain what is meant by "realisation" in this context, e.g. in a footnote, rather than create another link that the reader could (but probably won't!) follow? Djr32 (talk) 23:22, 15 November 2009 (UTC)

Right, except it should be "as well as" rather than "rather than", and that the reader would be even less likely to read a footnote than a link. ___A. di M. 23:41, 15 November 2009 (UTC)

Most readers would not read either a link or footnote, but those puzzled by the phrase presumably would.--Michael C. Price ^talk 10:15, 16 November 2009 (UTC)

Um, why not just say "length"? --Michael C. Price ^talk 00:00, 16 November 2009 (UTC)

Good call, Michael - simple and direct language is exactly what was needed, methinks. Sebastian Garth (talk) 02:12, 16 November 2009 (UTC)

Not really, the length of the metre will not change with better experimental procedures, it is just that we will know better what the length is. Unfortunately, the jargon exists for a reason. Martin Hogbin (talk) 05:20, 16 November 2009 (UTC)

You have a point. In which case there is no magic word and we really need a blue-link from "realisation".--Michael C. Price ^talk 10:05, 16 November 2009 (UTC)

proposed "Numerical value, notation and units"

see User:Wdl1961/sandbox1

Wdl1961 (talk) 20:31, 13 November 2009 (UTC)

I just reverted some of that that a couple of you guys put into the article. The Savard ref is fine for the conversion that people wanted, but we should stick close to what that ref says, and not go extrapolating for the fun of it. Dicklyon (talk) 20:33, 14 November 2009 (UTC)

It's not extrapolation just for the fun of it. The longer form is the "correct" form in imperial notation. The shorter form is just in miles. Both have their distinctive merits, so include both. --Michael C. Price ^talk 07:53, 15 November 2009 (UTC)

The evidence suggests it's just for the fun of it. You got your pointless conversion in by finding a source for it; isn't that enough? You have to push for another weird conversion? Dicklyon (talk) 06:42, 16 November 2009 (UTC)

Remember WP:AGF. The miles only form was not suggested by me.

You're the one who looks like you have some weird agenda. You objected on grounds of verification, so I introduced an intermediate step and you removed it. You say it requires sourcing, yet this is another routine calculation that doesn't require sourcing. You just don't like it and you're struggling (and failing) to find a policy violation to back up your prejudices. I've given you a reason for inclusion; please address that.

--Michael C. Price ^talk 10:32, 16 November 2009 (UTC)

Exact speed in SI units

I left this subject for a while to see what would happen and the answer is, 'not very much'. Unlike the original FA version and Britannica, the lead still does not state at the start that the value for the speed of light in SI units is exact. Despite that, we have the same figure in the lead three times. This is a hangover for the pre-arbcom days which needs to be adressed.

Although there are some interesting issues of physics and philosophy surrounding the subject, the basic concept is not that hard for most people to understand. The length of the metre is based on the speed of light and the second, therefore the value of the speed of light in metres per second is fixed. We should state this at the start.

Am I on my own here or is it just that nobody has go round to fixing it yet? Martin Hogbin (talk) 12:34, 15 November 2009 (UTC)

I agree, it should be fixed and the duplication should be removed. The lead is way to long and repetitive. The 3rd paragraph is redundant and can be deleted entirely. --Michael C. Price ^talk 13:05, 15 November 2009 (UTC)

Done. History and exactness are spelt out in detail in the main text, so we didn't need them in the lead.--Michael C. Price ^talk 16:41, 15 November 2009 (UTC)

But you have only eliminated the history (for what reason I'm not sure) and not the exactness ... and isn't the lead supposed to be some sort of summary? Abtract (talk) 17:12, 15 November 2009 (UTC)

The spelling out of the history was eliminated. The exactness was not spelled out to begin with. DVdm (talk) 17:21, 15 November 2009 (UTC)

I agree with what I think is Abtract's point, that the lead should be a summary, and one shouldn't simply delete one section of it, instead of keeping it and reducing all the sections appropriately, keeping in mind Martin's point regarding redundancy. --Bob K31416 (talk) 17:31, 15 November 2009 (UTC)

But we don't have to summarise everything in the main text in the lead. The history of the subject is probably only going to interest historians of science. Anyway, I felt the paragraph was just way too long. Perhaps a shortened version could be inserted (although a synopsis might be difficult). --Michael C. Price ^talk 17:44, 15 November 2009 (UTC)

Re "Anyway, I felt the paragraph was just way too long. Perhaps a shortened version could be inserted..." - That makes sense to me. The other paragraphs should be considered for shortening too, in my opinion. Could we restore the deleted paragraph and work on a shortened version? --Bob K31416 (talk) 17:54, 15 November 2009 (UTC)

There's an inconsistency between the restored history in the lead and the main text in the "redefinition of the metre". Is the date 1975 or 1972? BTW can we use $\pm 1.1$ instead of (1.1)? The latter is less accessible by the general readership, IMO. --Michael C. Price ^talk 10:56, 16 November 2009 (UTC)

Second sentence in the lead

'This constant is significant in the understanding and study of astronomy, space travel and other fields'. The much greater significance of c (spacetime constant) is is covered in the next paragraph, The above sentence, in so far as it makes any sense at all, follows from that.

This sentence should be removed or replaced with a more general statement along the lines of, 'This constant is important in many areas of physics'. Martin Hogbin (talk) 14:13, 16 November 2009 (UTC)

• I thought the original looked sorta awkward too. Your version is acceptable to me. --Bob K31416 (talk) 15:07, 16 November 2009 (UTC)

• Support. That sentence has been bothering me as well. (TimothyRias (talk) 15:30, 16 November 2009 (UTC))

• Support Martin's version, or better "It is an important constant in many areas of physics." ___A. di M. 16:22, 16 November 2009 (UTC)
• Basically support, but how about "despite its name, it has wide significance in many areas of science." Physchim62 (talk) 17:55, 16 November 2009 (UTC)

• I support removing the sentence in question with no replacement. We don't need to editorialize here. --agr (talk) 18:50, 16 November 2009 (UTC)

• Support. Sebastian Garth (talk) 21:44, 16 November 2009 (UTC)

Alt display proposals

The speed of light (usually denoted c) is a physical constant, and is the speed at which electromagnetic radiation, such as light, travels in vacuum. Its value is exactly

c = 299 792 458 m/s

Wdl1961 (talk) 17:08, 16 November 2009 (UTC)

• Oppose. Physchim62 (talk) 17:55, 16 November 2009 (UTC)

• Why would you want that? TimothyRias (talk) 18:08, 16 November 2009 (UTC)

• Are you serious? (BTW, I've fixed the header level, as this is not about the "This constant is significant" sentence. I've also moved agr's comment where (unless I'm missing something) it belongs.) --___A. di M. 19:51, 16 November 2009 (UTC)

• Personally, I think that it reads just fine the way it is. What would be the point of using the larger/bolder font, anyway? Sebastian Garth (talk) 20:10, 16 November 2009 (UTC)

Approximate and exact values in lede

I think that the simpler to understand and very notable values for the speed of light, are the approximate values 300,000 km/s and 186,000 mi/s. If they were in the lede, they would help adhere to the principle of starting an article with simpler info that appeals to the greater number of readers. Perhaps we can put them in the lede in addition to the exact value that is already there? That way, the greater readership is served. The lede would look like the one in this version of the article. Also note that in this version of the lede, the exact value is indicated as "exact". The lede paragraph would look like this.

The speed of light (usually denoted c) is a physical constant, and is the speed at which electromagnetic radiation, such as light, travels in vacuum. Its approximate value is 300,000 kilometres per second or 186,000 miles per second. Its exact value is 299,792,458 metres per second. This constant is significant in the understanding and study of astronomy, space travel and other fields.

--Bob K31416 (talk) 15:07, 15 November 2009 (UTC)

P.S. I googled to investigate notability on the internet and found the following results.

1. "speed of light" 300,000:     51,400 results
2. "speed of light" 186,000:     50,500 results
3. "speed of light" 299,792,458: 26,900 results

--Bob K31416 (talk) 15:44, 15 November 2009 (UTC)

Oh yes, great. I googled too:

1. "speed of light" nonsense:     107,000 results
2. "speed of light" stupid:     185,000 results
3. "speed of light" variable:     471,000 results
4. "speed of light" wrong:     561,000 results

Congratulations DVdm (talk) 16:02, 15 November 2009 (UTC)

Yeah, and why are we listening to someone who can't spell lead and introduces new section breaks for no reason?--Michael C. Price ^talk 16:06, 15 November 2009 (UTC)

Michael, your ignorance is showing; see [3]. Dicklyon (talk) 22:42, 15 November 2009 (UTC)

Tell that to Merriam-Webster. --Michael C. Price ^talk 23:36, 15 November 2009 (UTC)

Did you mean this Merriam-Webster? Actually, I learned about this word when I came to Wikipedia and I saw it was used by other editors. When I first saw it, I think in a policy or guideline page, I almost changed it to lead, but I googled lede definition and found it was a legitimate word. --Bob K31416 (talk) 05:09, 16 November 2009 (UTC)

IMHO Both is overkill, exact only will confuse some casual readers, best is to start with the approximations only since more or less everyone will find this useful: casual readers will understand it, most students will only ever need 3X10^8 and experts will either already know the exact value or at the very least will know that one exists and will appear later in the body of the article (which is where it should remain. Abtract (talk) 15:50, 15 November 2009 (UTC)

Most readers never need any value for the speed of light, so let's drop the spurious need business. I agree both is overkill; is there a reader who does not realise that 300,000 is approximately 299792.458? WP:COMMONSENSE for heaven's sake. Why give an approximate value and then the exact? Just give the exact value. --Michael C. Price ^talk 16:05, 15 November 2009 (UTC)

(edit conflict)Abtract, I agree with you regarding having the approximations in the lede. But I don't think the exact value should be removed, since there is the statement regarding the fact that c is a physical constant, in which case I think its exact value should be specified. --Bob K31416 (talk) 16:09, 15 November 2009 (UTC)

I looked at 8 of our articles on fundamental physical constants. (Avogadro constant, Planck constant, Elementary charge, Boltzmann constant, Bohr radius, Faraday constant, Gravitational constant, Fine-structure constant) All show the best available value in the lede, None show approximations in the lede. We already show approximations in the infobox. That's more than enough, in my opinion. --agr (talk) 22:34, 15 November 2009 (UTC)

I say let the reader do their own rounding. An exact value seems sufficient to me. Sebastian Garth (talk) 23:08, 15 November 2009 (UTC)

Agree with you and Michael. 300,000,000 rather than 299,792,458 only "appeals to the greater number of readers" who have never used a £20 note to pay for something costing £19.98; all those who have can tell that 299,792,458 is about 300 million in less time than they can say "three hundred million" aloud. ___A. di M. 23:16, 15 November 2009 (UTC)

agr, I think that's a good attempt at analysis, in fact very good, but it neglects the fact that those physical constants don't appear in the popular press, etc. anywhere nearly as much as the speed of light, where it is usually referred to as 300,000 km/s or 186,000 mi/s, from my recollection. Don't you have the same recollection? Also note that this Speed of light article is more likely to be looked at by the general public without a scientific background, compared to the articles on those other physical constants, in my opinion. Everyone, please note that we are writing this article for the readers and not for ourselves. The lede is an especially sensitive part in this regard because this may be all that is read by people who don't have a background in science. The 9 digit exact value in metres just looks like a bunch of digits to most people who usually use km and miles for large distances. --Bob K31416 (talk) 03:46, 16 November 2009 (UTC)

We are a reference encyclopedia. See WP:NOT. People come to us seeking the best, most up-to-date information available on a subject. I too learned 186,000 mi/s, but back then that was pretty close to the known accuracy :) --agr (talk) 18:47, 16 November 2009 (UTC)

Bob, I absolutely agree ... readers first. Abtract (talk) 08:51, 16 November 2009 (UTC)

Yes, and I think readers want the facts, not some unnecessarily dumbed down approximation. If they really feel cerebrally challenged by an integer they can get the dumbed down value from the sidebar. --Michael C. Price ^talk 10:00, 16 November 2009 (UTC)

How about giving the exact value along with something like, 'often conveniently approximated to 300,000 km/s'. This covers anyone who may have thought that 300,000 is an exact figure. Martin Hogbin (talk) 13:57, 16 November 2009 (UTC)

And is there any reason to think that subset of people is non-empty? (especially if you take the subsubset of people that would not infer that little fact from seeing just the exact value given.) Having both figures there seems mildly insulting to the intelligence of the reader. Then again I don't have any real strong feelings against you suggestion. (As long as the proper value is given in the lede. (TimothyRias (talk) 15:41, 16 November 2009 (UTC))

Thanks for not having any strong feelings against it. To everyone, please recall the version that began this thread. Thanks. --Bob K31416 (talk) 15:56, 16 November 2009 (UTC)

Personally I don't have a problem with saying stating the common appromixations in km/s or mi/s (or m/s or ft/s) as long as the exact value is stated first. These ARE the values layfolk will have encountered more often than not, and so this is a point of clarification. Say what something is, but also say what it isn't. Footnotes would be the ideal place for this IMO. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 17:26, 16 November 2009 (UTC)

I too have no problem adding explanatory text such as "...often approximated as 300,000 km per second or 186,000 miles per second..." after the exact value is stated. However a footnote would be silly. We already show the approximations in the info box.--agr (talk) 18:47, 16 November 2009 (UTC)

For some reason, I dislike your version much less than all the other wordings proposed so far to introduce approximation. Matter of fact, I'm not even opposed to adding it. ___A. di M. 19:58, 16 November 2009 (UTC)

I really don't see the usefullness of the approximation, personally, but then again, I wouldn't necessarily be opposed to it being inserted after the exact value, either. Neutral. Sebastian Garth (talk) 20:31, 16 November 2009 (UTC)

Poll

It looks like we have a chance of reaching a consensus on one of the following versions:

1. Its approximate value is 300,000 kilometres per second or 186,000 miles per second. Its exact value is 299,792,458 metres per second.
2. Its exact value is 299,792,458 metres per second, which is approximately 300,000 kilometres per second or 186,000 miles per second.

   --Bob K31416 (talk) 20:57, 16 November 2009 (UTC)

3. Its {exact} value is 299,792,458 metres per second, often approximated as 300,000 kilometres per second or 186,000 miles per second. (Second half originally proposed by agr.)

   --___A. di M. 21:20, 16 November 2009 (UTC)

Option 1

Option 2

1. --Bob K31416 (talk) 21:07, 16 November 2009 (UTC)

1. Some variant on option 2 - my preferred wording would be "Its value is exactly 299,792,458 metres per second (approximately 186,000 miles per second).", or the same with the km/s approximation. Djr32 (talk) 21:30, 16 November 2009 (UTC)

Option 3

1. With or without the part within braces. ___A. di M. 21:22, 16 November 2009 (UTC)
2. With "exact". Dicklyon (talk) 21:24, 16 November 2009 (UTC)
3. [moved from comment written before option 3 was articulated] I prefer #2, except I think that the "which is approximately" part is fairly redundant (and almost insults the reader's intelligence). Perhaps "which is often approximated as" would be more appropriate? Sebastian Garth (talk) 21:23, 16 November 2009 (UTC)
   - Also favor inclusion of "exact". Sebastian Garth (talk) 21:36, 16 November 2009 (UTC)
4. With "exact".--agr (talk) 22:43, 16 November 2009 (UTC)
5. With "exact". I like the phrase 'commonly approximated' because there are many possible approximations to the exact number, but these particular ones turn up all the time in physics problems, and there's a good chance the reader here finds that relevant. LouScheffer (talk) 12:26, 17 November 2009 (UTC)
6. With "exact". --Bob K31416 (talk) 14:25, 17 November 2009 (UTC)

None

1. Giving three values in such close proximity is overkill imho and may confuse. I favour starting with the SI approximation in the first para and with the exact SI figure at the end of the history part of the lead. I see no need for the mps figure other than in the info box. Abtract (talk) 12:01, 17 November 2009 (UTC)

No Poll

1. For those who think this talk page has become a kindergarten again. DVdm (talk) 17:15, 17 November 2009 (UTC)
2. Amen to that. --Michael C. Price ^talk 18:58, 17 November 2009 (UTC)
3. Empathic agreement. Wikipedia is not a democracy. TimothyRias (talk) 19:12, 17 November 2009 (UTC)
   - Hmmm. Taking a poll on not having a poll. : ) --Bob K31416 (talk) 21:40, 17 November 2009 (UTC)

• Wikipedia is not a democracy but "Consensus is Wikipedia's fundamental model for editorial decision-making." (WP:Consensus) Polls are often a useful tool in building consensus and I think that's been the case here. --agr (talk) 21:48, 17 November 2009 (UTC)
  • in [..] article editing, polls are generally not used.--Michael C. Price ^talk 07:07, 18 November 2009 (UTC)

    Yeah, that suggestion makes perfect sense because normally polls cause more drama than everything else; but this has not been the case for this one. Whatever works... ___A. di M. 14:17, 18 November 2009 (UTC)

Comments

• I added "neither". --Bob K31416 (talk) 21:11, 16 November 2009 (UTC)
• I added "Option 3", and changed "Neither" to "None" accordingly. --___A. di M. 21:20, 16 November 2009 (UTC)
  • I had considered something like Option 3 which has "often approximated", but I think if it was put in the article it would be unstable because someone would come along and object to it as OR. --Bob K31416 (talk) 21:27, 16 November 2009 (UTC) On second thought, perhaps this isn't a problem. --Bob K31416 (talk) 15:13, 17 November 2009 (UTC)
• This is going to very rapidly become another hopelessly confused poll. Is the question whether to have exact-then-approximate or approximate-then-exact, or are we trying to pick the exact wording? As it stands, exact-then-approximate will split the vote between 2 and 3 (which I see as variants on the same thing). Djr32 (talk) 21:30, 16 November 2009 (UTC)
  • Option 3 does seem to have confused things a little. Please note if we didn't have Option 3, the differences between Options 2 and 3 could still be implemented after the main point of this poll is implemented, without being against consensus, since it wouldn't have been a subject of the main point of the poll. --Bob K31416 (talk) 21:38, 16 November 2009 (UTC) Update: It looks like it's working out OK, and I switched from Option 2 to Option 3. --Bob K31416 (talk) 15:13, 17 November 2009 (UTC)
    • They are not orthogonal issues. I'm not opposed to adding approximations; I'm fiercely opposed to add approximations in any way that insults the intelligence of the reader. 299,792,458 is approximately 300,000,000? We know that. Prices such as $29.97 have been used for decades, and anyone older than 6 and younger than 80 can tell that it's nearly thirty dollars and nowhere near twenty dollars in less than one second. 299,792,458 is often approximated as 300,000,000? This is slightly less self-evident and more interesting. Slightly, but that's enough for me to oppose the former and support the latter. ___A. di M. 10:47, 17 November 2009 (UTC)
      • Agreed. Funny how we don't have an option with no approximations. --Michael C. Price ^talk 11:36, 17 November 2009 (UTC)
        • The option for no approximations is "None", since it would have kept the article as it was. (Originally, when there were two options, the choice for no change was "Neither", which would have kept the article as it was, without approximations. When a third option was added, the choice was changed to "None" by an editor other than me, with presumably the same meaning intended.) --Bob K31416 (talk) 14:22, 17 November 2009 (UTC)
          • None can also mean "none of the above but still not happy". Hence the entire poll is meaningless.--Michael C. Price ^talk 17:04, 17 November 2009 (UTC)
            • I have added a meta-option for "No Poll". DVdm (talk) 17:15, 17 November 2009 (UTC)
            • I guess whoever "votes" "None" is supposed to explain what he wants, and so far the only person signing there did that. I'd add a "Option 0 (status quo)", were it not that the status quo right now (as of 17:39, 17 November 2009 (UTC)) happens to coincide with option 3. --___A. di M. 17:39, 17 November 2009 (UTC)
  • Please note that any variant that is consistent with the main point of this poll (i.e having SI and imperial approximations, with exact or approximations first) could be put in later, with the ordinary editing process, after the result of this poll is implemented. --Bob K31416 (talk) 21:48, 16 November 2009 (UTC)

Constant speed in inertial frames

In the above section we currently have, '...by which the one-way speed of light becomes equal to the two-way speed of light and assumed that the synchronization method could be applied consistently all over the frame. Later it was proven that the assumption of consistency could be removed provided the two-way speed of light on the given inertial frame was a constant (see Einstein synchronisation) as experiments have indeed confirmed to be'. I am not sure who added this and when but I cannot make much sense of it. Does anyone want to defend or explain it or should it be rewritten or removed? Martin Hogbin (talk) 11:37, 22 November 2009 (UTC)

Was inserted here by anonymo. Throw it out and see what happens :-)

DVdm (talk) 11:52, 22 November 2009 (UTC)

Edit summary questions

Re edit summary questions in a recent edit of A. di M.,

1. "More specifically" than what? - than vacuum and non-vacuum
2. why is visible light singled out that way? - because the general public thinks "visible light" when the word "light" is used.

Regards, --Bob K31416 (talk) 20:36, 22 November 2009 (UTC)

c in Imperial units

This part of Numerical value, notation and units struck me as not very meaningful. Just my opinion.

"Using the common official definitions of the mile (1609.344 metres), the yard (0.9144 metres), the foot (0.3048 metres) and the inch (0.0254 metres), the speed of light can be expressed exactly in imperial units as 186,282 miles, 698 yards, 2 feet, and 5+21⁄127 inches per second."

Perhaps it should be deleted? I'd appreciate the opinions of other editors. --Bob K31416 (talk) 23:05, 8 November 2009 (UTC)

Did you see the earlier discussion?--Michael C. Price ^talk 23:29, 8 November 2009 (UTC)

Thanks for the link to the previous discussion. It looks like a majority of the 5 editors in that discussion wanted it in. I'm not sure of its intended purpose since I don't think anyone would use it for calculations. I guess it was considered an interesting fact. Anyhow, I'm not pressing it. Regards, --Bob K31416 (talk) 23:57, 8 November 2009 (UTC)

Yes, just an interesting fact. --Michael C. Price ^talk 23:59, 8 November 2009 (UTC)

Re. "I don't think anyone would use it for calculations": the same applies to the 26st digit after the point of pi, and yet that article gives 35 digits in the lead and 50 digits in the body. :-) ___A. di M. 23:14, 9 November 2009 (UTC)

Personally, I think it's an example of what is normally prohibited in wikipedia, original research (see WP:NOR), notwithstanding the comment there that "This policy does not forbid routine calculations, such as adding numbers, converting units, or calculating a person's age, provided editors agree that the arithmetic and its application correctly reflect the information published by the sources from which it is derived." The trouble is that such a conversion is anything but routine, and the idea that the speed of light is exact, and therefore needs to be expressed down to fractions of an inch per second, is not an idea that connects in any meaningful way to the system of imperial units. The conversion calculation is too complicated to be routine, and is probably beyond the abilities of almost any reader to even check. It's useless trivia, even if correct. And now that one more person has questioned it, I'd like to ask again why anyone feels it should be in there. I think it debases the article. Dicklyon (talk) 02:18, 9 November 2009 (UTC)

The conversion calculation is too complicated to be routine, and is probably beyond the abilities of almost any reader to even check. Really? --Michael C. Price ^talk 02:28, 9 November 2009 (UTC)

Gee whillikers! I checked it by calculation. I think it is synth because of the "exact" aspect, but I don't have a problem with it for that reason. I think it just looks ugly and takes up too much space. Just a comment. Like I said, I'm not pressing it. --Bob K31416 (talk) 02:42, 9 November 2009 (UTC)

OK, maybe I overstated that point. Perhaps 5 or 10 percept of our readers would be able to do the conversion; once they realize that 1/127 inch is 0.2 mm and that they can add up everything in mm and expect to get an integer answer, and if they have a calculator with enough digits, or a big enough sheet of paper, and some patience, anyone that's reasonably competent would be ABLE to do it. And now two of you have done it, congrats. But how does it help the article? Dicklyon (talk) 02:47, 9 November 2009 (UTC)

Hey, I guess it's hard to tell the players without a score sheet. I don't think it helps the article.

BTW, google this: 186282 x 1609.344 + 698 x 0.9144 + 2 x 0.3048 + (5 + 21 / 127) x 0.0254 =

et voilà! --Bob K31416 (talk) 03:11, 9 November 2009 (UTC)

Neat - and my calculator gives the exact result as well.--Michael C. Price ^talk 03:32, 9 November 2009 (UTC)

As we saw earlier, "Generally, conversions to and from metric units and US or imperial units should be provided ... Converted values should use a level of precision similar to that of the source value ..." Open and shut case, I'd say. --Michael C. Price ^talk 02:44, 9 November 2009 (UTC)

The concept of "level of precision" is certainly problematic here. If the exact value is an integer number of meters, should we provide an exact imperial value that requires a precision of 1/127 inch? Hardly an open-and-shut case. Dicklyon (talk) 02:47, 9 November 2009 (UTC)

Nothing problematic at all. The metric value is given exactly, therefore the imperial value is as well. Just following orders! --Michael C. Price ^talk 02:50, 9 November 2009 (UTC)

I understand that's what you're doing, but I disagree that that is the intent of "use a level of precision similar to that of the source value". What is the "level of precision" of an exact value? How would you translate a speed limit of exactly 100 km per hour to imperial units? Dicklyon (talk) 02:57, 9 November 2009 (UTC)

I don't see that question debated on the physics fora. Obviously not notable enough. But I'm open minded about it; feel free to add such conversions. --Michael C. Price ^talk 03:07, 9 November 2009 (UTC)

(edit conflict)Just for the sake of discussion, could you outline the steps used in getting that result by the editor who put it in? I.e. calculation, and how it was determined that it was exact. It seems that you don't feel that it is synth and I thought it would be interesting if that was the case. As far as I'm concerned, you don't have to hassle with it if you don't feel like it. I was just curious. --Bob K31416 (talk) 02:59, 9 November 2009 (UTC)

It's long division with the added irritant of repeated unit conversions. Start with c=299792458 / 1609.344 = 186282.397... That gives you the 186282 miles/sec. Then express the remaining decimal as a fraction (for exactness) and multiply by 1760 (=#yards per mile): the integer part is the yards/sec: 698. Repeat for feet, inches, and fractions of inches. --Michael C. Price ^talk 03:21, 9 November 2009 (UTC)

Only keep it if an exact duplicate is seen in a substantial number of regional textbooks. We have to keep some people happy.Wdl1961 (talk) 03:37, 9 November 2009 (UTC)

I'd settle for finding it in even one book or paper; so far we've only seen it in a discussion forum (and now in wikipedia and its mirrors). Dicklyon (talk) 06:34, 9 November 2009 (UTC)

I saw it in at least two fora. The interesting point is that the result was greeted with cries of incredulity. Hence we should report the exactness here, in its easily verifiable form. --Michael C. Price ^talk 09:09, 9 November 2009 (UTC)

Yes. As soon as we remove it, someone will show up and re-insert something similar, but not quite as carefully and precisely expressed. The calculation is trivial, all the data to verify it is included in the wikilinks (so this is definitely WP:NOTOR), and, strangely, there seems to be a real demand for this little fact. So let's keep it. DVdm (talk) 09:19, 9 November 2009 (UTC)

We could have a link to http://www.google.com/search?q=186282*1609.344+%2B+698*0.9144+%2B+2*0.3048+%2B+%285%2B21%2F127%29*0.0254 just in case the reader can't be arsed to do that trivial calculation themself. ___A. di M. 12:16, 9 November 2009 (UTC)

Excellent idea. DVdm (talk) 12:28, 9 November 2009 (UTC)

Agreed. Done. --Michael C. Price ^talk 13:53, 9 November 2009 (UTC)

<outdent>Actually, the google calculator result seems to have only 9 significant digits, so we can't check if the given Imperial units number is exact just from the google calculator's result. In fact, even if it had any large number of significant digits that we wanted, that still wouldn't prove exactness. Perhaps we need to look again at whether this can be considered a simple calculation that is allowed by WP:NOR, since proving exactness may be more complicated than a simple calculation. --Bob K31416 (talk) 15:18, 9 November 2009 (UTC)

Do you think that people will not notice the occurrence of 1/127 multiplied with 0.0254, giving exactly 0.0002? DVdm (talk) 15:32, 9 November 2009 (UTC)

I didn't immediately notice that, so I guess I should answer your question with yes, I think that people will not notice that occurrence. BTW, do you feel that alone is a proof of exactness? --Bob K31416 (talk) 15:40, 9 November 2009 (UTC)

Do you see any other division in the expression?

Apart from that, I agree with you that the google calculation is no proof of the exactness of that particular result, as can be shown with what happens with the google result when we replace 0.0254 with 0.0253 and compare with happens when you do the sae with a high precision calculator. DVdm (talk) 16:35, 9 November 2009 (UTC)

[4] is (marginally) better. It yields a non-zero result if you replace the 21 with 20.99 (but not with 20.999). ___A. di M. 17:10, 9 November 2009 (UTC)

As a side note, using a a calculator to show exactness does not work in general. See, for example, "Strange Series and High Precision Fraud" by J. M. Borwein and P. B. Borwein. Here they show, for example, a rapidly converging series that appears too converge to an integer, but actually diverges from the integer value roughly *half a billion* zeros after the decimal point. LouScheffer (talk) 16:27, 12 November 2009 (UTC)

BTW, would using 5+42⁄254 be any better than 5+21⁄127 for that matter? ___A. di M. 22:59, 9 November 2009 (UTC)

Undue weight

it violates the letter and spirit of wp:Undue weight.

besides there in no consensus.Wdl1961 (talk) 14:09, 9 November 2009 (UTC)

Re undue weight, there are millions of readers (non-scientists) for whom the imperial units are their frame of reference. --Michael C. Price ^talk 14:15, 9 November 2009 (UTC)

and nobody bothered with :698 yards, 2 feet, and 5+21⁄127 inches per second.Wdl1961 (talk) 14:25, 9 November 2009 (UTC)

I would agree with Wdl1961 on this. For imperial units, it seems like expressing c in just miles per second is more appropriate. The extra parts seem only interesting to those who are interested in the purely mathematical aspects of numbers, rather than the speed of light. --Bob K31416 (talk) 14:37, 9 November 2009 (UTC)

Indeed, there is no consensus to remove it. It was here before Wdl1961 and Bob Knnnnn arrived, so let's keep it. DVdm (talk) 15:07, 9 November 2009 (UTC)

How 'bout a straw pool?

Pool

How should the end of the first paragraph of Speed of light#Numerical value, notation and units read?

Option 1. Give exact value in imperial units (i.e. status quo)

... The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s. Using the common official definitions of the mile (1609.344 metres), the yard (0.9144 metres), the foot (0.3048 metres) and the inch (0.0254 metres), the speed of light can be expressed exactly in imperial units as 186,282 miles, 698 yards, 2 feet, and 5+21⁄127 inches per second.

Option 2. Say that the value in imperial units is exact, but do not give it.

... The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s. Since the yard is itself defined as exactly 0.9144 metres, the speed of light can also be expressed exactly in imperial units.</ref>

Option 3. No mention of imperial units in section 1

... The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s.

Comments

The exact speed of light in metric units is specified 11 times in the article. The imperial value is mentioned once. Now, what was that about undue weight?--Michael C. Price ^talk 17:25, 9 November 2009 (UTC)

Michael, How many times does the metric version appear in the literature outside of Wikipedia, which is what we are trying to use to make an encyclopedia, versus how many times the Imperial units version appears outside of Wikipedia? I'm not sure if your 11 times in the article for 299,792,458 m/s is correct. Seems more like 5. But considering what's outside Wikipedia, I think not including the Imperial units version that is currently in the article, is consistent with its non-use in literature outside of Wikipedia. --Bob K31416 (talk) 19:59, 9 November 2009 (UTC)

Definitely more than 5. More like 10 or 11.--Michael C. Price ^talk 01:54, 10 November 2009 (UTC)

So I guess we now have:

Option 1b

... The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s. Using the common official definition of the statute mile (1609.344 metres), the speed of light can be expressed exactly in imperial units as 186,282+39,937⁄100,584 miles per second. (Or the same, only with feet instead of miles.)

Option 3b

... The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s.^*

---

^* Using the common official definitions of the mile (1609.344 metres), the yard (0.9144 metres), the foot (0.3048 metres) and the inch (0.0254 metres), the speed of light can be expressed exactly in imperial units as 186,282 miles, 698 yards, 2 feet, and 5+21⁄127 inches per second.

___A. di M. 22:51, 9 November 2009 (UTC)

Option 3c -- just to show how lame 3b is.

... The effect of this definition is to fix the speed of light in vacuum at exactly 299792458 m/s.^*

---

^* Using the common official definitions of the mile (1609.344 metres), the yard (0.9144 metres), the foot (0.3048 metres) and the inch (0.0254 metres), the speed of light can be expressed exactly in imperial units as 186,282 miles and 699 yards per second.

Dicklyon (talk) 07:25, 12 November 2009 (UTC)

I fail to see how this achieves anything other than muddy the waters. How does quoting an incorrect value and citing a calculator value show anything. Yes, the Google calculation is meaningless but the underlying logic is sound. It should reference the agreement defining the yard in metres, not some two-bit calculator. CrispMuncher (talk) 12:02, 12 November 2009 (UTC)

Dicklyon, I do wish you would reconsider Option 3b. Please try to picture how much removing the disputed passage from the main text, and putting it in a much less prominent footnote, will help. --Bob K31416 (talk) 13:17, 12 November 2009 (UTC)

21/127 should be preserved in a footnote.Wdl1961 (talk) 14:29, 12 November 2009 (UTC)

Preferences

• Support option 1 (first choice) and option 2 (second choice). --___A. di M. 15:56, 9 November 2009 (UTC)[See below. ___A. di M. 22:54, 9 November 2009 (UTC)]
• Support option 1 (first choice) and option 2 (second choice). DVdm (talk) 16:35, 9 November 2009 (UTC)
• Support option 1 (first choice) and option 2 (second choice). --Michael C. Price ^talk 17:12, 9 November 2009 (UTC)
• Option 1 (in feet per seconds, not the horrible mix of imperial units), or Option 2 (equal preferences). Categorically oppose giving c in the horrible mix of imperial units given above. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 17:31, 9 November 2009 (UTC)
  • You do realise that imperial units are intended to be expressed as a mixture? --Michael C. Price ^talk 17:37, 9 November 2009 (UTC)
    • Says who? Can you provide a single example of a distance given in miles, yards, feet and inches in modern usage?--agr (talk) 18:53, 9 November 2009 (UTC)
• Support option 3 .place dif between 1 and 3 in a footnote.that should be an option 4.Wdl1961 (talk) 18:09, 9 November 2009 (UTC)
• I am not happy with any of the choices. We should give the exact value in imperial units, but there is not need for all the drama. Option 1 is a caricature of imperial usage. Texts that give the speed of light in imperial usage invariably do so in miles per second. Also there is no need to recite the definitions of miles, yards, feet and inches. One definition is enought. Also we should make clear that we are talking about the U.S. statute mile (since the U.S. is the main user of imperial units). I would suggest:

Using the current definition of the statute mile (1609.344 metres), the speed of light can be expressed exactly in imperial units as 186,282 miles, 2096 feet, and 5+21⁄127 inches per second. --agr (talk) 18:53, 9 November 2009 (UTC)

• Support Option 3b option 3 or "Option 4" mentioned by Steve in the next message or option 3 with Wdl1961's footnote, or using only miles per second, or Headbomb's version of only ft per second, or agr's version where he has removed the units conversions and yards of the version that is currently in the article. In any case, I don't like option 1 since not very informative, takes up too much space for what it has to say (especially the metric conversions), and seems to encourage readers to think, "What the hell is this doing here?". --Bob K31416 (talk) 19:08, 9 November 2009 (UTC)

• What happened to option 4: "... The effect of this definition is to fix the speed of light in vacuum at exactly 299,792,458 m/s.[2][3][4] (This is around 186,000 miles per second, see table at right for other conversions.)" That's the one I support. No reader needs more than 0.1% accuracy. Having more than 0.1% accuracy for SI is only necessary because of the definition of the meter, which is relatively important. --Steve (talk) 22:35, 9 November 2009 (UTC)
  • I like that one a lot! It's now my first choice. --Bob K31416 (talk) 01:36, 10 November 2009 (UTC)
  • (edit conflict) The point is showing that the SI is not unique in having an exact speed of light... ___A. di M. 22:51, 9 November 2009 (UTC)

But would that be of any interest? Evidence that it isn't, is that it doesn't appear to be in any of the literature outside of Wikipedia. At least none have been found so far. Isn't the bottom line that editors report what is in the literature, rather than come up with their own facts that they are interested in? --Bob K31416 (talk) 01:36, 10 November 2009 (UTC)

AdiM and Michael C Price: It seems you're worried that readers will think "the speed of light cannot be exact in any unit system except SI". Why do you think that? What is there in the article that implies that? Maybe I'm interpreting y'all wrong, but it looks to me like the sole purpose of this is to correct a misperception that Brews Ohare and/or David Tombe may (or may not) have had. If so, that's not a good reason, those are only two people. We should correct common and natural misconceptions, not every single possible bizarre misconception that any one person in the world has. (Anyway, even if you do want to make that point, I'd somewhat prefer using the examples c=1 exactly in natural units, or c=1 light year per year exactly.) --Steve (talk) 06:34, 10 November 2009 (UTC)

It seems you're worried that readers will think "the speed of light cannot be exact in any unit system except SI". Why do you think that? because that's what I saw, as mentioned previously, on various physics fora. --Michael C. Price ^talk 10:44, 10 November 2009 (UTC)

Re. "1 light year per year", the lead of the Spanish article has "or equivalently 9.46×10¹⁵ m/year; the latter figure is used to define the interval called light year". (Not that I think that'd be useful in the lead of our article; but perhaps somewhere in section 1.) --___A. di M. 11:36, 10 November 2009 (UTC)

I meant the point of using imperial units in that particular paragraph is to show that. If we don't want to say that c/(mi/s) is exact, there's no point in mentioning imperial units there. But I'm not opposed to keep the approximations, too, where they are now (and possibly elsewhere, as it's not that "elegant" that some piece of info can only be found in a table in a picture caption!). --___A. di M. 11:36, 10 November 2009 (UTC)

• Support option 1 (first choice), options 1b (see #Comments above) and 2 (equal second choices), and option 3b (third choice). ___A. di M. 22:51, 9 November 2009 (UTC)
• Stick to sources – who cares about all the preferences, if most of them don't respect WP:V or WP:RS? Does any source point out that the SOL is exact in imperial units? If not, why would we want to do so here? Does any source report the exact value in imperial units? If not, why should we? Give us reasons, not just opinions on what you like. Dicklyon (talk) 05:10, 10 November 2009 (UTC)
  • As has been repeatedly pointed out, routine calculations do not require sources. That why they're calculations. --Michael C. Price ^talk 10:42, 10 November 2009 (UTC)

How do you measure 5+21⁄127 inch? Wdl1961 (talk) 05:56, 10 November 2009 (UTC)

Using a micrometer, for example. (If the point is "how do you measure any length to within 0.7 parts per trillion", then it's much more valid, though not 100% relevant.) ___A. di M. 11:36, 10 November 2009 (UTC)

There is no measuring device on the market with 127 division dials that i have seen. Pls give refs so we can measure it. Useless info is not relevant. Wdl1961 (talk) 12:53, 10 November 2009 (UTC)

There is no measuring device on the market for neutrinos. That doesn't mean we don't write about them. --Michael C. Price ^talk 14:52, 10 November 2009 (UTC)

Are you kidding? 1⁄127 of an inch is 0.2 mm; the crappiest vernier calliper you can find will be twice as precise than that, and, according to micrometer there are vernier micrometers 100 times as precise as that (or, if you insist that they must be marked in inches, 78 times as precise as that). Now precision doesn't imply accuracy, but what we're discussing about is a calculation, not a measurement. ___A. di M. 15:32, 10 November 2009 (UTC)

Right now as I'm typing this, the calliper in the other room reads 5.00 cm and 1+124⁄128 in. (That's the thickness of one of the lead blocks we use to shield ourselves from radiations.) --___A. di M. 16:26, 24 November 2009 (UTC)

Michael, Here's the Routine calculations section from the policy WP:NOR.

Routine calculations

This policy does not forbid routine calculations, such as adding numbers, converting units, or calculating a person's age, provided editors agree that the arithmetic and its application correctly reflect the information published by the sources from which it is derived.

Please note that last important part of it: "provided editors agree that the arithmetic and its application correctly reflect the information published by the sources from which it is derived." With this in mind, Dicklyon's point is quite germane, and you haven't yet satisfactorily responded to it, in my opinion. --Bob K31416 (talk) 11:14, 10 November 2009 (UTC)

The key word is "information". The imperial expression reflects the same information as the metric expression. --Michael C. Price ^talk 11:18, 10 November 2009 (UTC)

Instead of picking and choosing individual words out of context, which are not any more "key words" than other words in the quote, we should look at all the "key words" and phrases. For example "agree", "correctly reflect", etc. With that in mind, could you answer Dicklyon's question, "Does any source point out that the SOL is exact in imperial units?" The fact that the speed of light can be expressed exactly in imperial units appears to be an idea that originated with wikipedia editors, rather than an idea that appears in a reliable source. The "exactness" idea does not correctly reflect the information published by the sources, since no source expresses that non-obvious idea that the speed of light can be expressed exactly in imperial units. Thus it is a violation of WP:NOR. --Bob K31416 (talk) 11:47, 10 November 2009 (UTC)

OK, so it's not obvious that if two numbers are known exactly their ratio is also known exactly, and you want a source for that. Gibbs, Philip (1997). "How is the speed of light measured?". Usenet Physics FAQ. University of California, Riverside. Retrieved 2009-11-10. Since the inch is defined as 2.54 centimetres, the speed of light also has an exact value in non-metric units. --___A. di M. 12:08, 10 November 2009 (UTC)

Bob, I'm not taking things out of context. It is not a violation of NOR. We have seen that routine calculations are allowed, no matter how you and Dicklyon try to deny it, and we've seen that not only are unit conversions permitted they are actually expected and with the same degree of exactness. This is not cherry picking. Jez! --Michael C. Price ^talk 12:25, 10 November 2009 (UTC)

(edit conflict)If the point is that the exact value itself is close to the border line of WP:OR (though outside Wikipedia anyone would laugh on hearing it called "original research"), what about: "Since imperial units are nowadays defined as an exact number of metres (e.g. the statute mile is 1609.344 m), the numerical value of c in imperial units is also exact by definition, e.g. 186,282.397... miles per second." (Wording needs tweaking.) Now, taking an ordinary pocket calculator (provided it has at least nine digits), typing 299792458÷1609.344=, and copying the first nine digits of the result is not original research by any stretch of imagination. ___A. di M. 11:53, 10 November 2009 (UTC)

(edit conflict)Although I had to filter out a lot of remarks in the above that I don't think were productive, there was one part that was useful. It was

Gibbs, Philip (1997). "How is the speed of light measured?". Usenet Physics FAQ. University of California, Riverside. Retrieved 2009-11-10. Since the inch is defined as 2.54 centimetres, the speed of light also has an exact value in non-metric units.

--Bob K31416 (talk) 12:58, 10 November 2009 (UTC)

(edit conflict)I've made an attempt at a note along the lines suggested by A. di M. (talk · contribs). My preference is for option 1: I think this is exactly the kind of barely relevant factoid that has made Wikipedia famous and makes people actually want to read the encyclopedia! If we take ourselves too seriously, we destroy one of our main "selling points" (should that be "giving-away points", as we don't actually charge for this?) – that we contain information that other encyclopedias don't. On a slightly more serious note, can we not use the expression "statute mile": plain "mile" would be better, or "international mile" if we want to be precise. The term "statute mile" is ambiguous in many countries, not least the United States. Physchim62 (talk) 13:02, 10 November 2009 (UTC)

Re "I think this is exactly the kind of barely relevant factoid that has made Wikipedia famous and makes people actually want to read the encyclopedia!" - First time I've heard that one. I note even your characterization of the item with all the imperial units of miles, yards, feet, inches to the 1/127, as a "barely relevant factoid" does not speak well for it. Seems like your reason for wanting it in is that you think readers would appreciate it. Well, you're entitled to your opinion, and all I can do is express my opinion that I don't think they would. --Bob K31416 (talk) 13:21, 10 November 2009 (UTC)

It's not a matter of opinion. Readers of at least two physics fora (previously cited) found the matter very interesting. Why should the readers of Wikipedia be any different? --Michael C. Price ^talk 14:52, 10 November 2009 (UTC)

Could you give a link to those discussions so that we can see what you are referring to? Thanks. --Bob K31416 (talk) 15:13, 10 November 2009 (UTC)

FYI here's one of them, and another, and yet another --Michael C. Price ^talk 17:01, 10 November 2009 (UTC)

Thanks for the links. Regarding your comment, "Readers of at least two physics fora (previously cited) found the matter very interesting." I looked at those discussions and they didn't seem to support your remark about them being "very interested" in the type of form of the speed of light that combines miles, yards, feet, and inches, in my opinion. Regards, --Bob K31416 (talk) 18:28, 10 November 2009 (UTC)

So they're discussing it because they not interested?  :-) --Michael C. Price ^talk 18:33, 10 November 2009 (UTC)

They seemed to be more interested in other topics, rather than the type of form of the speed of light that combines miles, yards, feet, and inches. You might want to reread those discussions with my comments in mind. Regards, --Bob K31416 (talk) 18:39, 10 November 2009 (UTC)

P.S. From your comments elsewhere, it appears that this discussion is upsetting you. I'm not sure why. If you would like to discuss these personal issues, please come to my talk page. Under these circumstances, I don't feel like continuing this discussion with you. --Bob K31416 (talk) 19:02, 10 November 2009 (UTC)

Why? I did not appreciate you claiming that I took the word "information" out of context.--Michael C. Price ^talk 19:06, 10 November 2009 (UTC)

• Of those listed, I'd go for option 3b, or failing that nothing at all - I think we can justify not spending too much time on Imperial values in a scientific article where metric is pretty much universal. I certainly don't think we should clutter the main text with a side note of minor interest. I would prefer that the footnote was revised though, with just an exact conversion from the metric to the yard - the exact values of foot, inch etc are by derivation rather than by definition and in any case I think we can leave it the reader to compute the exact length of e.g. a foot if they so choose. CrispMuncher (talk) 19:54, 10 November 2009 (UTC)
• Option 3, with added detail in a footnote if it's really felt to be necessary (i.e. 3b). The fact that the SoL is an exact number in imperial units is a trivial consequence of the inch being defined as 25.4 mm (because 1 mm is therefore (5⁄127)", so the SoL is therefore 299792458 x 5000⁄127 inches/sec). In any case, just state it as a plain fact rather than all this "Using the common official definitions..." waffle. Djr32 (talk) 20:56, 10 November 2009 (UTC)

• To reiterate/elaborate, I prefer my "option 4" but I'm okay with option 2 or anything where the exact imperial speed of light is (at most) in a footnote. I'm strongly opposed to having the main text of the intro article talk about 127ths of inches, but I don't mind it in a footnote too much :-) --Steve (talk) 02:19, 11 November 2009 (UTC)
  • None of the options are about placing the text in the intro; they relate to its placement in a section.--Michael C. Price ^talk 02:24, 11 November 2009 (UTC)
    • Oh sorry. Good to know. I still stick with what I said, only replacing the word "intro" with "article", as above. --Steve (talk) 03:39, 11 November 2009 (UTC)

• I like something similar to option 4 as well, perhaps something like "Since the inch, and hence the mile, is defined as a rational fraction of the meter, the speed of light is also exact in imperial units*", with the detailed result in the footnote. I *like* the ugliness/sillyness of the full computation in terms of yards/feet/inches/fraction, since it shows why metric is useful. For example, would you prefer to find the round trip light travel time from a spacecraft in metric or imperial units? Given, for example, that the Rosetta spacecraft will be, at a particular time on the 13th, 30350.755732 kilometers (or 18859 miles, 150 yards, 0 feet, 2 and 63/64th of an inch) from the tracking station (actual example from the JPL spacecraft navigation web site). LouScheffer (talk) 16:27, 12 November 2009 (UTC)
  • Do you really mean 4? I thought that option threw away the exact imperial numbers. Anyway I agree with your sentiments; the unwieldiness of the imperial expression is one reason why we should display it in its full glory/ugliness. --Michael C. Price ^talk 18:09, 12 November 2009 (UTC)
  • Lou, For the Summary section below, would the following be an acceptable summary for you:
    • "LouScheffer:     similar to Steve's 1st choice (aka 4)"
  • --Bob K31416 (talk) 23:25, 12 November 2009 (UTC)

Additional Comments

• I changed my preference to only 3b to move this process along, and because I think it is a reasonable compromise. --Bob K31416 (talk) 02:27, 12 November 2009 (UTC)

• option 1 in a footnote (for obvious reasons). vote is for option no 3. Wdl1961 (talk) 02:49, 12 November 2009 (UTC)
  • Just checking, but it is unclear whether you mean to vote for option 3 since that option doesn't have a footnote. Please note that option 3b is the one with the footnote. --Bob K31416 (talk) 03:25, 12 November 2009 (UTC)
• Vote is for 3b. The 21/127 should be preserved in a footnote. Wdl1961 (talk) 03:35, 12 November 2009 (UTC)

Summary

The first list shows the editors and their choices. Editors may change their preferences above, new editors may give their preferences, and I will include those changes below. If there are any errors or omissions, please let me know. --Bob K31416 (talk) 01:28, 12 November 2009 (UTC)

1. DVdm:     1, 2
2. Michael C. Price:     1, 2
3. Headbomb:     ft/sec, 2
4. Wdl1961:     3b
5. agr:     same imperial units but with only one unit conversion and no yards, 3b
6. Bob K31416:     3b
7. A. di M.:     1, 1b, 2, 3b
8. Dicklyon:     did not choose except opposed to 1
9. CrispMuncher:     3b, 3
10. Djr32:     3, 3b
11. Steve:     approx miles/s (aka 4), 2, 3b

The multiple choices available and chosen by each editor, complicates the situation. So I tried to look at the simplest aspect first, i.e. whether the first choice of an editor is to keep the subject passage as is, or change it. I'm open to suggestions of how to proceed from here. One possibility is to eliminate Option 1 (because consensus is against it) and then make the next iteration. --Bob K31416 (talk) 21:10, 11 November 2009 (UTC)

One possibility is to eliminate Option 1 (because consensus is against it) eh? 1 is equal 1st in 1st votes and, surprise surprise, you want to eliminate it. --Michael C. Price ^talk 10:53, 12 November 2009 (UTC)

The "1st in 1st votes" that you refer to is only 3 out of 11 editors [note added: and ties Option 3b for 1st votes]. Against Option 1 is 8 out of 11 editors, which is a consensus. I also note that currently, 6 out of 11 editors find Option 3b acceptable, whereas only 3 out of 11 editors find Option 1 acceptable. --Bob K31416 (talk) 13:06, 12 November 2009 (UTC)

Rubbish. No other option exceeded 3/11 in 1st votes. You must think we're all really stupid. --Michael C. Price ^talk 13:12, 12 November 2009 (UTC)

WP:CIVIL Also, note that Option 3b had 3 first votes too, with currently twice as many editors finding it acceptable. --Bob K31416 (talk) 13:23, 12 November 2009 (UTC)

Pointing out that your wikilawyering is an insult to the intelligence of the editors is not a violation of WP:CIVIL. But, hey, don't let me stop you, remove option 1 and then we can all ignore everything you say. --Michael C. Price ^talk 15:23, 12 November 2009 (UTC)

Keep present version i.e. Option 1

1. DVdm
2. Michael C. Price
3. A. di M.

Change from present version

1. Headbomb
2. Wdl1961
3. agr
4. Bob K31416
5. Steve
6. Dicklyon
7. CrispMuncher
8. Djr32

Please note that the footnotes, e.g. in 3b, compare with 3c, provide a good illustration of why original research is a poor substitute for WP:V; the so-called "verification" given there is just wrong. Dicklyon (talk) 07:29, 12 November 2009 (UTC)

Yet there is not dispute that the calculation is correct.--Michael C. Price ^talk 10:56, 12 November 2009 (UTC)

Verification

It would be senseless to dispute it without working it out, but there's also no evidence that it is correct. Who has provided anything approaching a convincing verification, or even described a process for verifying it, other than my suggestion of multiplying it out by hand on a sufficiently large piece of paper? But even if we do that, a simple reading of WP:NOR and WP:V says it's not OK. This is not a routine units conversion. I'm at a loss to understand why you'd want to go there at all. After all the grief we went through when Brews was belaboring the implications of the exactness of the speed of light in meters per second, you missed all that fun, and decided to belabor it in a different way? Dicklyon (talk) 20:55, 12 November 2009 (UTC)

Actually I described the algorithm earlier. It's not hard (and doesn't require a bignum calculator). You say it isn't a routine units conversion. I say it is. --Michael C. Price ^talk 22:39, 12 November 2009 (UTC)

Well, yes, you did "describe" an algorithm on 9 November, but since it involved long division with repeating decimal fractions and conversions to rationals and such, it seemed more complicated that anyone here would likely have the patience to check. The easier algorithm would be to convert the integer part of the miles back to meters and subtract in the meter domain, keeping a precision of 0.0001 m, since that's enough to represent all inches and multiples thereof exactly; repeat with yards, feet, inches, and finally convert the inches to a fraction if you like; only long multiplications are needed, not divisions, since an ordinary calculator has enough precision to get the integer number of miles. Still, it's anything but a routine calculation, and beyond the ability of most readers to even check. But that's largely beside the point, as something so specific would really need to be sourced, per WP:V. Dicklyon (talk) 23:08, 12 November 2009 (UTC)

You are incorrect about the calculation's difficulty (as I said, I did it on my calculator without approximations). And no, there is no requirement that routine calculations be sourced. WP:OR is quite clear about that. It doesn't matter how often you deny it, white is not black. --Michael C. Price ^talk 23:32, 12 November 2009 (UTC)

I think you're either avoiding the truth or not understanding the question. You said below that you used pen and paper along with your calculator to do the long division. It would be interesting to know how you actually did it, and what fractional part of a mile you came up with, and how long it took you. Maybe someone else will volunteer to try actually doing it and see how long it takes. Dicklyon (talk) 02:59, 14 November 2009 (UTC)

Not evading anything. The fractional part is 39937⁄100584. BTW I have poor arithmetical skills; if I can do it, so can any competent physicist. --Michael C. Price ^talk 06:28, 14 November 2009 (UTC)

Dicklyon, I agree with your criticism of using the calculator since that doesn't prove exactness, especially since the number of significant digits of the google calculator is only 9. Exactness hasn't been proven here in a mathematically rigorous way. However, please note:

Gibbs, Philip (1997). "How is the speed of light measured?". Usenet Physics FAQ. University of California, Riverside. Retrieved 2009-11-10. Since the inch is defined as 2.54 centimetres, the speed of light also has an exact value in non-metric units.

--Bob K31416 (talk) 14:01, 12 November 2009 (UTC)

If you're going to argue that the physic forum FAQ is a reliable source, maybe we could use that. I don't mind pointing out the SOL is exact in systems whose length unit defined exactly in terms of the SI metre, as the inch is in many countries, but I'd rather based it on a more reliable source. Dicklyon (talk) 20:55, 12 November 2009 (UTC)

Note that the very same source is cited in footnotes 16 and 63 of the current version without even mentioning that it is a physics forum FAQ. ___A. di M. 23:49, 15 November 2009 (UTC)

P.S. I just realized a simple and mathematically rigorous way to prove that the imperial units version of the value for the speed of light is correct and exact. It would go along the following lines. First convert the exact metric version to inches using the exact conversion of 2.54  centimetres = 1 inch. (I think the part regarding the fractions of inches in 1/127 would work out OK because 254/127=2.) Then using the exact internal unit conversions in the imperial system of units, convert the inches to miles, yards, feet, and remainder inches, and check with the result in our article. Also, note that this result has appeared on other websites, although there is a question of whether those websites could be considered reliable sources. Cheers. --Bob K31416 (talk) 14:30, 12 November 2009 (UTC)

Yes, of course, you can do that, if you have a bignum calculator handy (like mathematica), or a big sheet of paper. But what would be the point? See WP:V. Dicklyon (talk) 20:55, 12 November 2009 (UTC)

You don't need any fancy calculator. I did the following computation in millimeters in Excel and checked it on my iPhone:

miles: 186282 X 1609344 = 299791819008 mm
yards: 698 X 914.4 = 638251.2
feet: 2 X 304.8 = 609.6
inchs: 5 X 25.4 = 127
+ 21/127 X 25.4 = 4.2

Total = 299792458000 mm

MOS:CONVERSIONS says we should show imperial units, in general, and with the same precision as the metric units. As I've said before, I think yards are superfluous. We could replace inches with a fraction of a foot to further simplify, but there is nothing out of the ordinary here as far as unit conversion goes.--agr (talk) 13:27, 13 November 2009 (UTC)

Your calculation is certainly correct; it only remains to show that your Excel and your iPhone do integer arithmetic to better than 12 digit accuracy, which they do. And it was clever to notice that doing it in mm instead of metres would let you use integers at that one step that needs "bignums". Most likely, Excel would have given you an exact decimal fraction in metres as well, but that might be harder to verify, since the intermediate internal representation is not exact (Matlab, for example, prints 2.997918190080000e+08, which is exact). Of course, manual verification of the last digit or two is also easy, so you don't have to dig into your calculator's documentation to convince yourself that it's right. The forward conversion path, however, remains somewhat trickier; it still hasn't been show by anyone herer how the conversion to fraction is easily done with a calculator. Michael Price wrote express the remaining decimal as a fraction (for exactness) but gave no clue how he did that, starting from the approximate decimal that he showed. Dicklyon (talk) 18:52, 13 November 2009 (UTC)

express the remaining decimal as a fraction (for exactness) means use pen and paper along with your calculator to do the long division. Or at least that was how I did it. And you do get an exact expression. --Michael C. Price ^talk 01:28, 14 November 2009 (UTC)

OK, thanks for clarifying that you do need to resort to pencil and paper, since calculators don't natively do rational math. And of course it's obvious that you do get an exact answer, since you start with exact conversion factor and an exact distance in meters. I never really doubted that you had it right, just pointing out that the method is far from routine or obvious. It is not a simple conversion, in the sense provided for in WP:NOR. Dicklyon (talk) 02:55, 14 November 2009 (UTC)

Complete claptrap as usual. There is nothing unusual or non-routine in using pen and paper. --Michael C. Price ^talk 06:18, 14 November 2009 (UTC)

The guideline makes no mention of using combined units of miles, yards, feet, inches, instead of just one imperial unit. Also, the guideline makes no mention of whether the imperial units should be provided in a footnote or in the main text. As I mentioned before, I would accept the imperial units version in a footnote, which is Option 3b. Currently Option 3b leads among the contenders. It is tied for 1st choices with 3 of 11 editors, and has the most acceptance with 6 of 11 [update: 7 of 11] editors. --Bob K31416 (talk) 15:55, 13 November 2009 (UTC)

"Nothing out of the ordinary"? Can you show us a single example in wikipedia of the conversion of an exact metric quantity to an exact imperial quantity, other than a unit conversion factor? Dicklyon (talk) 18:29, 13 November 2009 (UTC)

Most of the examples in the MOS guideline are in the body of the article. Footnotes are suggested for obscure units, board-feet is the example given. Since we are talking about an appropriate headed section of the article, not the lede, I don't see a need to bury the exact imperial value further. As for format of the conversion, here are the choices:

• 186,282 miles, 698 yards, 2 feet, and 5+21⁄127 inches per second
• 186,282 miles, 2096 feet, and 5+21⁄127 inches per second
• 186,282 miles, 2096 656⁄1524 feet per second
• 186,282 39937⁄100584 miles per second

Any exact conversion will require a fraction with a multiple of 127 in the denominator. I think miles, feet, inches looks the least ugly because the fraction is smaller, but I can live with any of the last three.--agr (talk) 17:18, 13 November 2009 (UTC)

Regarding the appropriateness of putting it in a footnote, so far I don't think anyone has provided a reliable source for this form of the exact value in imperial units. I understand that we can calculate it from the SI units, but it doesn't seem very notable, especially compared to the form in SI units which appears in many reliable sources that includes authoritative sources. Putting it in a footnote is currently accepted by 6 of 11 [update: 7 of 11] editors, and is the most accepted of all the options. I understand that everyone won't be completely satisfied by any one option, but perhaps it is best to settle on Option 3b, which keeps the imperial units expression in the article but in a footnote, and is the most accepted option. --Bob K31416 (talk) 17:56, 13 November 2009 (UTC)

We don't need a source for a simple unit conversion, but if putting the converted value in a footnote will bring about consensus, that is a reason I can accept.--agr (talk) 18:17, 13 November 2009 (UTC)

Thank you. I appreciate your willingness to compromise, and I have compromised from the other side of the issue. That now makes 7 of 11 editors accepting Option 3b. --Bob K31416 (talk) 19:33, 13 November 2009 (UTC)

I'm on record as being against burying unsourced, OR, and POV stuff in footnotes; Brews used to do that a lot, trying to get away with including unsourced interpretations and personal expositions and such. What's wrong with respecting WP:V and WP:NOR here? Dicklyon (talk) 18:29, 13 November 2009 (UTC)

I understand your concern, but whether or not one agrees that it is a violation of policy, there's the policy WP:IAR, and 10 of 11 editors accept it for the article in either a footnote or in the main text. Also, note that some editors who don't like it are willing to compromise and put it in a footnote. --Bob K31416 (talk) 19:35, 13 November 2009 (UTC)

The insertion has been made . Hopefully it is in full accordance with option 3b. Maybe is is the worst solution or maybe the best solution but the result and the process of getting there is certainly educational . Wdl1961 (talk) 05:11, 14 November 2009 (UTC)

Disruption

I find that Bob K31416 is disrupting the talk page. What do others say? DVdm (talk) 15:39, 10 November 2009 (UTC)

Agreed. --Michael C. Price ^talk 18:39, 10 November 2009 (UTC)

That is the purpose of the talk page.Wdl1961 (talk) 16:24, 10 November 2009 (UTC)

No, the purpose is article improvement, not disruption.--Michael C. Price ^talk 18:39, 10 November 2009 (UTC)

I really couldn't find any evidence of bonafide misbehavior on his part, personally. Perhaps you could explain in more detail what exactly you find so disruptive? Sebastian Garth (talk) 16:50, 10 November 2009 (UTC)

I don't think that's necessery. Most of the current contributors know what I mean. If you don't, no problem, it's not very important anyway, just a bit amusing. DVdm (talk) 17:11, 10 November 2009 (UTC)

I can't see any problems either. Perhaps some editors here are suffering from post traumatic stress syndrome after fighting all these battles against Brews? Count Iblis (talk) 16:54, 10 November 2009 (UTC)

Perhaps some editors here are suffering from post traumatic stress syndrome after fighting all these battles against Brews? I've been thinking that myself recently, and not just here. The bad vibes seem all over the physics pages, even from editors that are normally paragons of level-headedness.--Michael C. Price ^talk 16:57, 10 November 2009 (UTC)

From where I am standing, it is a bit as if Bob K31416 and Wdl1961 have stepped right into the Brews' and Tombe's shoes. Is it a coincience that the count is here as well? Bizarre. Perhaps it's just perception. Ah well, who cares anyway? DVdm (talk) 17:08, 10 November 2009 (UTC)

I have tried to break these endless circular arguments. if that is disruptive so be it. Please dont categorize me . i have been in discussions with Nazis and communist when i was twelve years old during ww2 politely your "reasoning/reality " is not very impressive , sorry.Wdl1961 (talk) 15:25, 11 November 2009 (UTC)

Took it out

Given the lack of support for putting the unsourced exact imperial value in the text, I took it out. Let's work on what more we can say that is sourced, instead of quibbling about the test way to include unsourced OR. Dicklyon (talk) 03:29, 14 November 2009 (UTC)

I found an extensive set of web pages by John J. G. Savard of Edmonton, Alberta, Canada (formerly of the University of Alberta) [5] with one [6] that states "The speed of light in a vacuum can also be given in units of the uniform US/British inch of 2.54 centimeters, which leads to light travelling 186,282 miles, 698 yards, 2 feet, and 5 21/127 inches every second in a vacuum." Many Wikipedia pages have external links to John Savard's web pages, most in the area of cryptography. He is cited in several cryptography and computer books as an authority. He published an article in the journal Cryptologia (1999). His website includes the online book A Cryptographic Compendium which is cited in WorldCat. Because this version of the speed of light touches on cryptography, he appears to be a suitable reference.

The standard Microsoft Windows 32-digit calculator (Start-Programs-Accessories-Calculator) does not have enough digits to show a repeating decimal for 21/127. Using a clue from the Bad Astronomy and Universe Today Forum that 39937/100584 contains a 42-digit repeating decimal, I used a sheet of paper to find 21/127 is the 42-digit repeating decimal 0.165354330708661417322834645669291338582677. — Joe Kress (talk) 06:49, 14 November 2009 (UTC)

OK, we don't need the repeating decimal (and no n-digit calculator will tell you that it's repeating, right?), but the source you found for the conversion to US/British units should be useful. I call for a citation in the footnote with the unsourced conversion. Dicklyon (talk) 06:56, 14 November 2009 (UTC)

Glad you find the source useful. I had previously supplied it, but now that you have it from someone else perhaps you'll accept it.--Michael C. Price ^talk 07:00, 14 November 2009 (UTC)

I must have missed that. Dicklyon (talk) 07:15, 14 November 2009 (UTC)

A calculator would need more than 84 digits to show that a number has a 42-digit repeating section. The only 'calculators' with that many digits are programs whose calculations are limited only by computer memory, such as Mathematica or REXX. — Joe Kress (talk) 07:29, 14 November 2009 (UTC)

No, you're wrong. Seeing the same 42 digits twice is not adequate to conclude that it's a repeating decimal. Dicklyon (talk) 20:32, 14 November 2009 (UTC)

Joe Kress wrote:

"A calculator would need more than 84 digits to show that a number has a 42-digit repeating section."

Not really. Unless the denominator d of the fraction has a factor of 2 or 5 (not the case here) the period of its decimal expansion is the smallest positive integer p such that 10^p − 1 is divisible by d, and this must also be a divisor of the value of Carmichael's λ-function evaluated at d. Using your calculator to do arithmetic modulo d, you can find p without ever needing to evaluate numers with any more digits than d ² has (i.e. 5 digits, if d = 127).

—David Wilson (talk · cont) 23:23, 14 November 2009 (UTC)

Re "Using your calculator to do arithmetic modulo d, you can find p without ever needing to evaluate numers with any more digits than d ² has (i.e. 5 digits, if d = 127)." -

Since 10⁴² - 1 is a 42 digit integer, how do you evaluate (10^42 - 1) % 127 without ever needing to evaluate numbers with any more digits than 5? Thanks. --Bob K31416 (talk) 02:18, 15 November 2009 (UTC)

(ec)

10² = 100 ≡ −27 mod 127; ∴ 10⁴ ≡ (−27)² ≡ 729 ≡ 94 ≡ −33 mod 127; ∴ 10⁸ ≡ (−33)² ≡ 1089 ≡ 73 ≡ −54 mod 127; ∴ 10¹⁶ ≡ (−54)² ≡ 2916 ≡ 122 ≡ −5 mod 127; ∴ 10³² ≡ (−5)² ≡ 25 mod 127; ∴ 10⁴⁰ ≡ 10³² × 10⁸ ≡ 25 × −54 ≡ −1350 ≡ 47 mod 127; ∴ 10⁴² ≡ 10⁴⁰ × 10² ≡ 47 × −27 ≡ −1269 ≡ 1 mod 127; ∴ 10⁴² − 1 ≡ 0 mod 127.

—David Wilson (talk · cont) 07:58, 15 November 2009 (UTC)

David, thanks for the lesson in number theory, but it is incomplete. I do not know number theory, so please perform the modular arithmetic you describe on this talk page so that I can understand it for the case of 127. Would this guarantee that no digits precede the repeating portion, as is the case for 21/127? Or could another numerator generate a few non-repeating digits before the 42-digit repeating portion begins? Does a factor of 2 mean that the number of digits in the repeating portion cannot be determined, or does it mean that an unknown number of non-repeating digits could occur before the repeating portion? Because the miles per second proper fraction, 39937/100584, has a 42-digit repeating portion and its denominator, 100584=127×11×3²×2³, has a factor of 127, I suspect that its 42-digit repeating portion occurs because of that factor. It has three digits before its 42-digit repeating decimal even begins:

39937/100584 = 0.397051220870118507913783504334685437047641772. Can the number of those non-repeating digits be determined before the number is calculated? Otherwise, many more digits than the number in the repeating portion might be needed in order to determine the actual decimal equivalent of the proper fraction. Because I used long division to determine the decimal equivalent of 21/127, I recognized that when I obtained a remainder of 21, the same remainder (numerator) I began with, the decimal equivalent would begin to repeat. — Joe Kress (talk) 07:22, 15 November 2009 (UTC)

It sounds like you understand it just fine; the key is that you need to look at the remainder, not just quotient digits. There may be a number theory trick to find how many 9's it takes for 999...9 to be divisible by 127, but I don't know of one simpler than long division of 127 into 1000... and looking for a remainder of 1. Dicklyon (talk) 07:40, 15 November 2009 (UTC)

Though now that I say that, it's obvious that dividing into 999... would also work, stopping at a remainder of 0. Dicklyon (talk) 07:41, 15 November 2009 (UTC)

The first number theory trick you need to reduce your work is the fact I mentioned above—namely, that the number of 9's you need must be a divisor of λ(127), where λ is Carmichael's function. For prime numbers p (which 127 is) λ(p) = p − 1. So for the case p = 127, λ(p) = 126, and the number of 9's it took could only have been 3, 6, 7, 9, 14, 18, 21, 42, 63 or 126 (you can obviously eliminate 1 and 2 immediately by inspection).

The second trick, for avoiding doing a long division of 127 into 10ⁿ − 1 for each of the possible values of n, is to use arithmetic modulo 127, as I do above.

—David Wilson (talk · cont) 08:36, 15 November 2009 (UTC)

To avoid cluttering up this talk page with further off-topic material, I have answered some of Joe Kress's other questions on my talk page.

—David Wilson (talk · cont) 12:12, 15 November 2009 (UTC)

It turns out that one of the answers I gave initially on my talk page was not quite right. I have now corrected it.

—David Wilson (talk · cont) 11:06, 18 November 2009 (UTC)

There is no need for repeating decimals to convert the speed of light from metric to imperial. Any calculator will tell you 299792548 m in miles is 186282 plus a fraction.

186282 miles X 1609344 mm/mile (exact) = 299791819008 mm

The fraction then is 299792458000 mm - 299791819008 mm = 638 992 mm

The speed of light is then exactly 186,282 + 638 992/1609344 miles/s. You can reduce the fraction, dividing by the common factor of 16, to get 186,282 39937⁄100584 miles per second.

If you want inches, 638992 mm / 25.4 mm per inch = 25157.16...; 25157 inches X 25.4 mm per inch = 638987.8 mm

638992 mm - 638987.8 mm = 4.2 mm. 4.2/25.4 = 21/127.

So the fraction of a mile is 638992 mm = 25157 21/127 inches. But 25157 inches / 12 inch per foot = 2096 feet 5 inches.

The speed of light is thus 186282 miles 2096 feet 5 21/127 inches per second. --agr (talk) 13:57, 15 November 2009 (UTC)

Another proposal

What about saying that the value of c in Imperial is exact in the text, but giving the exact value itself in the footnote? E.g.,

...The effect of this definition is to fix the speed of light in vacuum at exactly 299,792,458 m/s. Since the yard is itself defined as 0.9144 metres, the value of c in imperial units is also fixed, for example 299,792,458⁄1609.344 = 186,282.397... miles per second.^[15]

[15] The exact value is 186,282 miles, 698 yards, 2 feet, and 5+21⁄127 inches per second. Savard, John. "From Gold Coins to Cadmium Light". John Savard's Home Page. Retrieved 2009-11-14. {{cite web}}: External link in |work= (help) Archived version 2009-11-14

That way, 1) the fact that SI units aren't unique in that c is exact in them is shown also to readers who don't read footnotes; 2) there is a conversion to units familiar to laymen in the US in a place which isn't a footnote or a picture caption (right now, there's no such thing). (Also, someday I'll get around separating footnotes only containing citations from those containing additional info not in the body text.) ___A. di M. 00:05, 16 November 2009 (UTC)

I certainly agree that we should say that the imperial value is exact in the main text. --Michael C. Price ^talk 00:11, 16 November 2009 (UTC)

I don't like the phrasing "...the value of c in imperial units is also fixed..." for reasons I'd rather not belabour (it's no surprise that multiplying a fixed quantity by a constant value yields a fixed quantity!). I'd prefer the phrasing the second sentence as "Since the yard is defined as exactly 0.9144 metres, the value of c in imperial units can also be calculated exactly^[15]." Note that it also drops the numbers (the bit 299792458⁄(1760*0.9144) could, if retained at all, be moved to the footnote, while the approximation defeats the purpose). The problem then is that the imperial figure gets lost. So some variation "...299,792,458 m/s. This is approximately 186,282.4 miles per second; since the yard...."

Constant speed in inertial frames

This statement, 'In non-inertial frames (gravitationally curved space or accelerated frames), the local speed of light is constant and equal to c, but the speed of light along a trajectory of finite length can differ from c, depending on how distances and times are defined', is not supported by the quoted source. What is a 'trajectory of finite length'? This is not mentioned in the source or the link. It seems to me to be non-standard language.

The quoted source actually supports my wording by saying, 'The problem here comes from the fact that speed is a coordinate-dependent quantity, and is therefore somewhat ambiguous. To determine speed (distance moved/time taken) you must first choose some standards of distance and time, and different choices can give different answers'. Martin Hogbin (talk) 20:59, 27 November 2009 (UTC)

I think what was meant is that in GR you can (in general) only define infinitessimal distances in a unique way. So, the situation is worse than just a matter of choosing standards. Count Iblis (talk) 21:20, 27 November 2009 (UTC)

The fact that, in an inertial frame, the speed is c clearly defined has already been made. The point that I was making was that, in general, speeds including the speed of light in GR are not uniquely defined. 86.139.24.90 (talk) 22:46, 27 November 2009 (UTC)

Yes, but locally this is the same issue as in inertial frames: You are free to choose any coordinate system and the way you defne your local time coordinate does not have to be consistent with the way you define your patial coordinate. But that's a trivial issue. The non-trivial issue is that in GR you cannot (in general) define distances and time intervals globally in an unambiguous way. Count Iblis (talk) 23:46, 27 November 2009 (UTC)

Which is exactly what I wanted to say. Martin Hogbin (talk) 13:24, 28 November 2009 (UTC)

Article organization

I think that the overall organization of the article can be improved. Since any such improvement will involve some major changes to the article I think it better to discuss before being bold. (I'm also unsure what the best way forward will be.) The issues: (it might be useful to respond to each separately.)(TimothyRias (talk) 15:13, 27 October 2009 (UTC))

• Measurements and History Currently, all information about measuring techniques for the speed of light are contained in the history section. Now, this made a lot of sense when these sections discussed the increasing accuracy of measurements ultimately leading up to the redefinition of the metre, but some of the recent expansions have brought it beyond that scope. Might it not be better to have a separate section discussing various techniques for measuring the speed of light. (It would be nice if we could have one that does not use light, but I'm unaware of anything of sufficient notability in that extent.) This might be more in line with what a reader will expect from a history section.(TimothyRias (talk) 15:13, 27 October 2009 (UTC))

  I think that just promoting the last two subsections (which I'm going to do) will fix that. All of the rest of "History" deals either with very early measurements, or with measurements in metres per seconds which are now moot. ___A. di M. 21:28, 27 October 2009 (UTC)

  That is at least marginally better, but leaves us with a second level section of only a single sentence. (Lab demo). Is there some useful way we can expand on that? (TimothyRias (talk) 08:45, 28 October 2009 (UTC))

• Propagation of Light I think it might be a good idea to merge all the section that deal with the propagation of actual light. This would mainly involve the sections Nature of Light and Light in Transparent Media, but could also absorb the "variations with frequency" part of the variations with time and frequency section. This will help the article discriminate between the propagation speed of light and the fundamental spacetime constant speed of light. As it stands I fear that some readers may still come away from the article with the impression that the properties of spacetime depend on the speed with which light travels and not the other way around.(TimothyRias (talk) 15:13, 27 October 2009 (UTC))

• Fundamental Importance in Physics I am not sure about the title and content of this section. Anybody already familiar with the mentioned material will know that the treated subjects are of fundamental importance, but I'm not convinced that a reader with hardly any knowledge of physics will recognize them as such. This might be helped by including a nice introductory paragraph at the beginning of the section explaining that that the speed of light pops up all over physics. But I can't help to think that there might be a better way of organizing the material covered in that section.(TimothyRias (talk) 15:13, 27 October 2009 (UTC))

Any thoughts? (TimothyRias (talk) 15:13, 27 October 2009 (UTC))

Agree with the other two points. ___A. di M. 21:28, 27 October 2009 (UTC)

That might all be OK. To me, what's important is more the "fundamental importance" stuff than the details of the measurement, the history, and the exact value. These all need to be in there, but the reader really probably wants to know what's so special about "the speed of light". And as many physics book do, I'd introduce it in the opening paragraph as "about 3 time 10^8 ms" instead of the distracting and relatively useless exact value, which can follow in a subsequent paragraph. Dicklyon (talk) 23:46, 27 October 2009 (UTC)

I'm not sure how that is a reply to the points on organization of the article I brought up. Lets leave discussing the lead for another thread, and until after we have hammered out the main content. (TimothyRias (talk) 08:40, 28 October 2009 (UTC))

Another issue:

• The overall length of the article The article has recently breached the 100K mark. Now, this isn't a disaster per se, but if we are going to attempt to get the article through FAC we need to be able to be able to argue that these length is really needed for this article. I'm not sure that it is. Currently, the article strays a lot into topics that are related to the speed of light, such as the nature and behaviour of light, and the effects of special relativity. But special relativity and light already exist. I think we should try to get the article more into focus on the subject matter and more reliant on the existence of other articles. What is really essential to this article?

Some places where I think we can conserve space:

1. The article currently spends 4 paragraphs to discussing Ole Christensen Rømer's calculation of the speed of light. This by itself is probably notable enough to have its own article. Moving the material to its own article and expanding it further, we can replace the mention here with a single summary style paragraph saving quit a bit of space, and improving the flow of the article.
2. The current Fundamental importance in physics section strays a lot towards the implications of special relativity. Can we reduce this to only a couple of paragraphs which succinctly state the role of the speed of light in SR (and consequently GR and QFT)?
3. Do we really need to mention photons? And if so, can we do this in a more organized manner?

(TimothyRias (talk) 14:34, 28 October 2009 (UTC))

1. I agree. While we're at it, "Ancient, medieval and early modern speculation" can be merged into [some article which I'm sure already exists, but can't tell where it is], and "Redefinition of the metre" can be merged into Metre, retaining two paragraphs for each of these.
2. "A couple paragraphs" is too little for the relevance of c in SR; that's essentially the reason why c is so important. (I'm not saying that all the five subsections of three paragraphs each in average which exist now are strictly necessary; but I wouldn't trim "Fundamental importance in physics" by more than 40% the current size.)

Fair enough, my main point was to increase the focus on what we really need to say. (TimothyRias (talk) 16:29, 28 October 2009 (UTC))

1. We should mention them; of course an extensive discussion about them wouldn't belong here, but I don't think that the one paragraph in "Light as photons" and the third paragraph of "Variations with time and frequency" are that excessive. What do you mean by "more organized manner", exactly? ___A. di M. 16:03, 28 October 2009 (UTC)

More structured in the sense that is probably best to sweep the discussion of photons and photon mass together in one section. The main reason to mention photons is that the photon being massless is the reason light travels with the speed of light. Once we mention photons are massless that would also be the best location to mention the experimental limits on the photon mass, and the implications of a non-zero photon mass for the propagation of light. (TimothyRias (talk) 16:29, 28 October 2009 (UTC))

I agree with comments about the Rømer stuff: in fact, there are some similar comments at Talk:Ole Rømer about creating a separate article for the details of the SoL determination. I might get round to it this afternoon, if real life doesn't get in the way!

I also think we should take as much of a hatchet as possible to the discussions of relativity. It may well be that we can't cut much, but the article is about the speed of light, not about special relativity, and I must beg to differ with A. di M.'s statement that relativity is the reason why c is important! I always get a little irritated when I see the section on "composition of velocities" in this article: the section is too short to explain it's point, but long enough to break the flow of the article… I would hit the delete button on it if I didn't think it would cause drama among other editors, so I'll suggest it here first! Physchim62 (talk) 12:51, 29 October 2009 (UTC)

I would not have any problems with that. The only thing this article needs to state is that according to SR c is maximum speed attainable for massive objects. (TimothyRias (talk) 17:15, 29 October 2009 (UTC))

Another area that looks a bit overgrown is the intro itself - the first paragraph would really be sufficient. Everything else could be merged into some other section of the article. For example, by paragraph:
#2 -> (new section) The Theory of Relativity (or such)
#3 -> History
#4 -> Refractive Index and Refraction
Besides improving the general flow of the article, it would allow the user to navigate the TOC without first having to scroll three pages of screen space. Sebastian Garth (talk) 03:32, 30 October 2009 (UTC)

Actually, no the lead needs to cover the content of the main article per WP:LEAD. The current lead is nor ideal, but I suggest focussing on hamering out the main content first and then adjusting the lead to follow suit. (TimothyRias (talk) 08:36, 30 October 2009 (UTC))

OK, I have been bold and preformed some of the suggested reorganization with respect to light. I have basically merged all the sections dealing with light, leaving out duplications and stuff that was very off topic. The result will require some polishing and stuff. But structure wise I think it is an improvement. (Moreover it has succesfully reduced the article length by 5K). (TimothyRias (talk) 16:36, 9 November 2009 (UTC))

Just noticed this section. Sorry, I'm a newcomer. Could you have made the changes incrementally so it would be easier to see what you did and evaluate it more easily? --Bob K31416 (talk) 19:37, 9 November 2009 (UTC)

This would have been a hard change to do incrementally, because it involved merging several subsections. For what it is worth here is the diff:

http://en.wikipedia.org/w/index.php?title=Speed_of_light&curid=28736&diff=324861608&oldid=324838588

And here is my user sandbox where I prepared the edit: http://en.wikipedia.org/wiki/User:TimothyRias/temp3

(20:29, 9 November 2009 (UTC))

I like the new overall organization better, even if the wording needs some copy-editing (gonna give it a try). Other things which could be rehashed: 1) "Fundamental importance in physics" might be shortened (do we need a whole subsection for the velocity addition formula?), and a good introductory paragraph or two could be added to it; 2) The first four paragraphs of "Early astronomical techniques" can be replaced by a one-paragraph summary, now that Rømer's observations have their own article; likewise, "Ancient, medieval and early modern speculation" can be merged into Light#Historical theories about light, in chronological order and "Redefinition of the metre" into metre, and then they could be replaced by a two-paragraph summary each; 3) looking at the Spanish Wikipedia article (the only featured one in a language I can understand), I see a section es:Velocidad de la luz#Comunicaciones which would very neatly fit in place of our two-line introductory paragraph of "Practical effect of the finite speed of light". I'm going to translate it into a sandbox of mine.Here's my translation; except for the removal of obviously irrelevant links and the addition of obviously relevant ones, it is a nearly-literal translation, without any attempt to improve it. (I seem to recall having read the same info in English, but I can't tell where; but maybe that's just a deja-vu.) ___A. di M. 23:25, 9 November 2009 (UTC)

Restructuring/shortening the "Fundamental importance in physics"

OK, how are we going to go about this. I think the best way maybe to make a list of things that absolutely have to be covered in the section, and then merging/rewriting the subsection to a single section with two or three introductory paragraphs and maybe one or two subsections. (Instead of the five disjoint subsection that currently make up this section.) My go at things to need to be covered:

1. The role of c is an invariant speed in special relativity, and Lorentz transformations in general.
2. Some of the consequence of the existence of this invariant speed. In particular, c being the maximal speed for particles and information.
3. The fundamental role of (local) Lorentz symmetry in modern physics, and how this introduces c as a parameter in modern theories like GR, QED, general QFT, etc.
4. Speculation on constancy of speed of light and experimental bounds.

Stuff that can go:

1. Velocity addition formula. (Those not belong in THIS article.)
2. Do we need the somewhat pedantic stuff about one-way speed of light? (Maybe we do, just putting it out there for discussion.)

Also, I suggest changing the title to "fundamental role in physics". This is less likely to invoke arguments based on differing opinions of what is important. (Although it still leaves the possibility of arguing fundamental).

Any thoughts? TimothyRias (talk) 15:37, 10 November 2009 (UTC)

Good. What was done these days is a good start, but I'd still have a more organized structure than the current no introductory text and four subsections one of which two sentences long (and with as many footnotes as nouns, if I counted correctly!). Maybe a one-sentence mention of velocity addition wouldn't hurt, though the section we used to have was waaay too much. ___A. di M. 20:14, 16 November 2009 (UTC)

Agree, I am not sure how to go about this exactly, which is why I was waiting for more input. (However people seem more interested in discussing trivialities involving imperial units.) One idea I had is to make a new top level section dealing with the SoL as a maximum speed. It would incorporate some material from "Fundamental role in physics" section as well as the FTL section. This would treat thease subject more thematically grouped, and give proper context for any statement made about this and their limitations. (The section about Cherenkov radiation would be ditched as it has nothing to do with c.) Is this a reasonable plan? TimothyRias (talk) 21:18, 17 November 2009 (UTC)

Before reorganizing that section, it might help to trim or rewrite the material there that's less relevant to its topic. Then knowing what you have to work with, you can reorganize it. Or maybe you're satisfied that it doesn't need trimming? Perhaps you can give the section title and subsection titles here, for what you want to construct. That might help in explaining the type of reorganization you want to make.

I agree with your point about Cherenkov radiation but would suggest reducing it to one sentence, rather than eliminating it. It might find a place where the speed of light in a medium is discussed. This might be given as an example that charged particles can travel faster than the speed of light in a medium, and what happens when they do. (Just an aside, I remember a sci fi book that wrote about a near-light-speed spacecraft that gave off Cherenkov radiation as it entered the solar system. Maybe there is a literature, movie, TV, etc. fiction aspect that could be added to the article?)

I can't speak for the others, but I haven't been ignoring you, but rather silently agreeing with the trimming that you have done. Also, since I was new to this article, I could just as easily work with your version, since a glance at what you were doing indicated that you were making reasonable changes. It did seem kinda weird to me too that so many editors were so active about a few sentences, while you were making major changes. It may be that they were silently agreeing too, or maybe the social interaction was more attractive to them than editing the article. Also, please keep in mind what I first brought up in my message here of Nov 9, that it would help if you were more incremental in your editing when possible, with descriptive edit summaries. --Bob K31416 (talk) 23:19, 17 November 2009 (UTC)

Here's a possible candidate for trimming from the section Speed_of_light#Spacetime_constant.

Change:

"In Einstein's theory of general relativity, c is still an important constant of spacetime. This spacetime is curved by the presence of matter and energy causing gravitation. Disturbances of this curvature, including gravitational waves, are predicted by the theory to propagate at the speed of light, although they have not been directly observed yet.

To:

"In the theory of general relativity, changes in spacetime curvature and gravity, including gravitational waves, are propagated at the speed of light c."

with appropriate references. --Bob K31416 (talk) 13:28, 18 November 2009 (UTC)

P.S. I could suggest other trims in that section too, but I'll wait and see how this suggestion is received first. --Bob K31416 (talk) 14:16, 18 November 2009 (UTC)

I agree about Cherenkov radiation, maybe one sentence about it can fit somewhere. Some readers might be unaware that "stuff can't go faster than light" is only true in vacuum.

I agree about an "in fiction" section — as Physchim62 says, ‘If we take ourselves too seriously, we destroy one of our main "selling points"’; but such a section should be kept very short; should it ever exceed two paragraphs, the excess stuff should be moved away to another article.

Being incremental is hard with major changes, but they should be thoroughly explained on the talk page. Maybe a "development page" could be useful.

I don't like your proposed wording very much. Most readers won't understand what "spacetime curvature" means in practical terms. (Maybe you could replace "and" with "causing", but it'd be unclear whether it's the curvature or the changes in it which cause gravity.) Also, I'd say "propagate" rather than "are propagated". And it'd rather not state a theoretical prediction with no experimental verification so far as it were a matter of fact.___A. di M. 20:20, 18 November 2009 (UTC)

Thanks for your feedback. Could you give your modified version, or would you like to keep that part of the article as is? Regards, --Bob K31416 (talk) 21:16, 18 November 2009 (UTC)

I agree it should be shortened, but I don't have a version of mine right now. I'll get working on that tomorrow. ___A. di M. 22:27, 18 November 2009 (UTC)

Thanks. One thing I should add for your consideration, is that the article General relativity is a featured article and thus it may be useful for readers who want to learn more about spacetime curvature, etc. If that featured article is lacking an explanation for a more general public, regarding spacetime curvature, etc., one might consider putting those explanations in the lede or elsewhere over there, rather than here. --Bob K31416 (talk) 10:05, 19 November 2009 (UTC)

There's an article Introduction to general relativity which is also featured. On the other hand, this doesn't mean one can write abstrusely on the grounds that "if the reader doesn't know this term, they can always follow the link" (see WP:NOT PAPERS, point 5). ___A. di M. 14:59, 19 November 2009 (UTC)

Thanks for pointing out Point 5. I think we have to weigh whether a short explanation here of spacetime curvature, which may not be long enough to accomplish the task, is worth the digression. I'm looking forward to seeing your approach. --Bob K31416 (talk) 15:59, 19 November 2009 (UTC)

<outdent>Here's another possibility.

According to the theory of general relativity, gravitational waves and changes in gravity, propagate at the speed of light c.

--Bob K31416 (talk) 11:36, 20 November 2009 (UTC)

I would recommend something along these lines:

• "According to the theory of General Relativity, gravity, which is the result of the curvature of space-time caused by the presence of matter and energy[28], also propagates at the speed of light, although this has not yet been directly observed.[29][30]" Sebastian Garth (talk) 13:21, 20 November 2009 (UTC)

For one thing, it seems to have what another editor thought was a problem, "Most readers won't understand what 'spacetime curvature' means in practical terms."

This isn't a problem with the possibility that I suggested. Also, it doesn't digress while clearly mentioning the relation between the speed of light and gravity. --Bob K31416 (talk) 14:59, 20 November 2009 (UTC)

(edit conflict) I think Garth's version would be fine. [By "what 'spacetime curvature' means in practical terms" I meant the fact that it is caused by the presence of matter and energy and in turn causes gravitation, which is kind of clear with the current version, unclear with your earlier version, clear enough with Garth's proposal, and moot with your more recent proposal. Of course I don't expect readers understand the formalism of GR, or even that they should. As for your version, it's fine, too (provided you replace the second comma with "also", and add a comma and "but this has not yet been directly observed" at the end).

BTW, I've taken a look at the whole section to see whether I could come up with a way to significantly improve it; but I think that could only be done with non-trivial changes to other sections. For example, I was thinking about adding an introductory paragraph explaining why Einstein postulated c to be constant in the first place, but the "c = 1/√ε0μ0" thing is found in a later section. Also, the subsection "Causality and information transfer" could be moved into "Faster-than-light observations and experiments", and then some duplicated info could be removed; but the section title would have to be reworked. Let's wait for TimothyRias's version. --___A. di M. 15:15, 20 November 2009 (UTC)

Changing the comma to "also" would be fine with me. One could add your suggestion that it hasn't been directly observed, at the end of the sentence. Although I don't think that is necessary since that is implied by "according to theory" without any mention of experiment. I would accept that addition to my version if that would help get consensus.

Is adding spacetime curvature necessary? Seems like just mentioning the connection between the speed of light and gravity is sufficient, clearer, and reads better than Sebastian Garth's version, in my opinion. --Bob K31416 (talk) 15:27, 20 November 2009 (UTC)

(edit conflict)As for the first point: Yes, but that theory is almost one century old, it has practical consequences (for example, in the GPS system), and most of its other predictions have been verified; someone who knows this, on reading such a sentence, might subconsciously assume that this has been verified experimentally. (Of course there would be no rational reason to assume that, so that's a minor point; but the cost of adding eight little words "but this has not yet been directly observed" is also minor.) As for the second point: No, I don't think it is necessary, but I don't think it's useless, either (i.e. I'm open to both versions). Let's see what other people think, though.

BTW, here's a draft of how I'd merge "Causality and information transfer" and "Faster-than-light observations and experiments". --___A. di M. 15:48, 20 November 2009 (UTC)

And as for the 3rd point, that my version reads better? --Bob K31416 (talk) 15:54, 20 November 2009 (UTC)

Yes. ___A. di M. 16:10, 20 November 2009 (UTC)

I think the merge draft looks good. Would it be worth mentioning (with references, of course) that it is possible to exceed the apparent speed of light, from the perspective of an accelerating body (eg: total acceleration obtained), or would that be too technical? Sebastian Garth (talk) 16:48, 20 November 2009 (UTC)

I started looking at your draft and comparing it with the article. I noticed that the Causality and information transfer section of the original article and your draft have a considerable amount of digression from the topic of the speed of light and need to be trimmed, in my opinion. I think we should do the appropriate trimming in the article before we reorganize. --Bob K31416 (talk) 21:30, 20 November 2009 (UTC)

Also, I noticed that you rewrote the first paragraph of Causality and information transfer . I don't think your rewrite is an improvement, you haven't mentioned that you had done that, and you haven't given a reason for why you would want to do that.

Perhaps there was a misunderstanding regarding whether I approved of your draft, before you added it recently to the article, which I undid. I hope this clarifies that we need to discuss it more, starting with the points I mentioned above, i.e. trim article before merging and the 1st paragraph that you rewrote. There may be other points too, as examination of your draft continues. --Bob K31416 (talk) 22:04, 21 November 2009 (UTC)

As for the first paragraph of my version, that's a merger of the first paragraph of "Causality and information transfer" and that of "Faster-than-light observations and experiments" as in the version you reverted to. Their contents mostly overlap with each other, so I don't see the point of repeating that info twice. What wording would you suggest for that? --___A. di M. 11:03, 22 November 2009 (UTC)

As I mentioned, I don't think your proposed 1st paragraph is an improvement of the first paragraph of the section Causality and information transfer, so at least that's better wording than what you have. Also as I mentioned, a better way to reorganize sections is to first trim them when that is indicated. Below, I proposed that we trim that section to one paragraph as shown. I didn't do any rewording, just deleting. After we come to an agreement on that, it may be more clear how to reorganize, including rewording the first paragraph if that is needed. Figuring out what to do with one paragraph, as far as reorganizing is concerned, is easier than dealing with a section that is about 4 times larger with a digression, as it is now. --Bob K31416 (talk) 14:36, 22 November 2009 (UTC)

I disagree with you assertion that is easier to first trim and then reorganize. I would say the exact opposite. By first reorganizing (which involves figuring out what we want to say), it becomes much easier to identify redundant and digressing material. (TimothyRias (talk) 10:44, 23 November 2009 (UTC))

Also, a section containing only the first paragraph of "Causality and information transfer" would be pointless, as practically all of what it says is repeated by the first paragraph of "Faster-than-light observations and experiments". ___A. di M. 11:24, 23 November 2009 (UTC)

<outdent>Thanks for both of your opinions. In my opinion, reorganizing would make it easier to identify material that is redundant with other parts of this article, but not to identify digressing material. I feel that by first removing the digressing material, that it will be more easy to identify the redundant material. Also, having less material to reorganize would make reorganizing more easy. The principle is simple: why carry around and reorganize material that can be thrown out beforehand. When people move their possessions from one room to another, they don't move the junk, but rather throw it out beforehand.

For example, I feel that in the "Causality and information transfer" section, the 2nd and 3rd paragraphs and the last 1/2 sentence of the first paragraph, and the light cone figure, are a digression. When those parts are removed, the remaining first paragraph can be better merged with another part of the article since it is more easily seen to what extent another part of the article repeats its ideas and which is better written.

Regarding digression, it would be helpful if both of you contributed opinions in the section "Trimming of section Causality and information transfer" below. --Bob K31416 (talk) 15:16, 23 November 2009 (UTC)

Trimming of section Causality and information transfer

Regarding the section Causality and information transfer, I suggest that we delete the last 2 paragraphs, the figure, and the last part of the first paragraph because they are a digression from the topic of the speed of light, in my opinion. The result would look like this:

Causality and information transfer

See also: Causal contact and Horizon problem

According to the theory of special relativity, causality would be violated if information could travel faster than c in some reference frame: in some other reference frames, the information would be received before it had been sent, so the "effect" could be observed before the "cause". Such a violation of causality has never been recorded.

--Bob K31416 (talk) 00:00, 21 November 2009 (UTC)

The shape of the cone is defined by the SoL. Keep it and associated text. --Michael C. Price ^talk 04:26, 21 November 2009 (UTC)

Re "The shape of the cone is defined by the SoL." - That isn't mentioned in the section under discussion, but rather there is a digression. I think that the explanation of the light cone should be left to other areas in Wikipedia where it is already discussed, for example Causality and prohibition of motion faster than light in the article Special relativity. --Bob K31416 (talk) 03:29, 22 November 2009 (UTC)

You might want to somehow link Relativity of simultaneity, maybe in the "See also" at the top. Also, while I agree that all that talk about the light cone is excessive, I wouldn't remove all of it; in articles about scientific topics which are likely to be read by non-scientific readers, such digressions are common (there are many of them in Electron, a FA), and not totally useless: something which is obvious to a scientist, to a layman it might not even occur to look up. (And, after all, the fact that it is the slope of null geodesics—in less fanciful terms, the light rays which form the surface of the light cone—is nearly the most important thing about c.) What about:

All the points of spacetime which can be reached from a point A by travelling at the speed of light in a straight line form the light cone of A. Causal effects propagating from A can only reach points in the interior of the upper part of the cone (the causal future of A), such as B in the picture, and can only reach A from the interior of the lower part of the cone (the causal future of A). Points outside the cone (such as C) cannot be reached by any causal influence originating from A, because whether C chronologically precedes, follows, or is simultaneous to A is dependent on the observer: see Relativity of simultaneity.

(Of course I'm not sure about the wording, but that's to show that you don't need two longish paragraphs to make that point.) --___A. di M. 12:53, 24 November 2009 (UTC)

I appreciate your attempt at giving a brief description of the light cone. Unfortunately, it may be too difficult a subject to briefly describe and it seems like it will end up being unclear and uninformative, and only understood by those who already know the subject. I think the subject is best left where it already appears in other articles, where it is appropriate to give it the space needed for an explanation. Also, the light cone is used for describing more details of the subject that is already mentioned in the 1st paragraph of the section, so it would be a digression from the topic of the speed of light if it were included. --Bob K31416 (talk) 02:16, 25 November 2009 (UTC)

New first paragraph for section Faster-than-light observations and experiments

The remaining first paragraph mentioned at the beginning of the section above, can be combined with a sentence from the first paragraph of the section Faster-than-light observations and experiments, to form the following new first paragraph for that section. (The section Causality and information transfer can then be deleted.)

According to the theory of special relativity, if an object were travelling faster than c relative to an inertial frame of reference, it would be travelling backwards in time relative to another frame and causality would be violated. An "effect" could be observed before its "cause". Such a violation of causality has never been recorded.

--Bob K31416 (talk) 07:26, 25 November 2009 (UTC)

The fact that it is practically unanimously thought to be impossible is more important, IMO, than the fact that it "has never been recorded". (Gravitational waves have never been recorded, either...) Also, causality is not the only reason for that. So I'd at least keep the "It is widely accepted that it is normally impossible for information or matter to travel faster than c for several reasons. One reason is that" part, appending your proposal at the end. Also, I don't see what's too bad with including "and would lead to paradoxes" That's obvious for a scientist, but might not be for some laymen.

Putting all together, my proposal is...

It is widely accepted that it is normally impossible for information or matter to travel faster than c for several reasons. One reason is that according to the theory of special relativity, if an object were travelling faster than c relative to an inertial frame of reference, it would be travelling backwards in time relative to another frame and causality would be violated. An "effect" could be observed before its "cause". Such a violation of causality has never been recorded, and would lead to paradoxes (see Tachyonic antitelephone for an example).

Maybe "and causality would be violated" could be replaced by "violating causality", and the footnotes moved to the end of sentence. ___A. di M. 13:35, 25 November 2009 (UTC)

Your last two suggestions regarding the "causality" phrase and moving the footnotes are OK. I think the first sentence that you suggested keeping has problems and the last part regarding the Tachyonic antitelephone does not work for me. For now, I would agree to keeping the 1st sentence as you suggested if we remove the last part after "recorded". We can settle these points regarding the first and last parts after we make the other changes, including deletion of the section Causality and information transfer, which we seem to agree on and are independent of these points. --Bob K31416 (talk) 14:24, 25 November 2009 (UTC)

What problems do you think the first sentence has? How about keeping "would lead to paradoxes" in the text but moving the reference to the antitelephone (back) to a footnote? --___A. di M. 15:16, 25 November 2009 (UTC)

Keeping "would lead to paradoxes" would be OK. Actually I like it after finding that it has a nice wikilink. Re antitelephone, OK in a footnote.

Here's the first sentence that is being currently discussed.

It is widely accepted that it is normally impossible for information or matter to travel faster than c for several reasons.

Is it widely accepted among experts? Is it widely accepted among the general public, especially those that have seen Star Trek? What does "normally" mean? (These are questions that I asked myself that I wouldn't be confident answering.) I think this statement, or a modification of it, needs a reliable source before it can be included. Also, it says "for several reasons" but I think only one is given in the Faster-than-light... section, viz. causality violation, which leaves the reader hanging as to what the other reasons are. --Bob K31416 (talk) 21:16, 25 November 2009 (UTC)

(edit conflict) "Widely accepted" means "widely accepted by anyone who knows what they're talking about and are not joking or trolling". "Normally" means "except in very weird situations such as the one which is mentioned in the footnote" (namely the effect which I can't even spell or be arsed to look up its spelling, which IIRC is of the order of less than 10×10⁻³⁶ in any realistic situation; if it didn't exist I would even drop the "normally"). As for "reliable source", I think any decent physics textbook would do that; or, if you want a source freely available on-line, this one which IIRC is already cited somewhere else in the article for some other reason. As for "other reasons", see sections 16 and 17 of the source I just cited (the reason our article already gives is their section 18). --___A. di M. 22:03, 25 November 2009 (UTC)

Please give the excerpt from the reliable source that supports the first sentence re "widely accepted" and show where it can be found in the reliable source.

Re "for several reasons", a connection of these reasons to the "widely accepted" remark has to be made in a reliable source. If it is "widely accepted", how do we know that it is widely accepted for those reasons? If it is "widely accepted", those people may accept it because they believe it is a maxim, without knowing the reasons. I suspect that most people who believe that nothing can go faster than the speed of light don't know or understand the reasons, but just believe it is a fact. --Bob K31416 (talk) 22:31, 25 November 2009 (UTC)

I made the reorganization in the article according to your proposal and modifications of it that we agreed on. --Bob K31416 (talk) 01:43, 26 November 2009 (UTC)

So, what about "It is normally impossible for information or matter to travel faster than c; one reason for this is that according to the theory of..."? --___A. di M. 12:36, 26 November 2009 (UTC)

That's better. It seems to me that "normally impossible" doesn't read right. The word "impossible" is usually used as an absolute, i.e. "impossible" seems to mean "always impossible" rather than sometimes impossible and other times possible. One could say that something is impossible under certain conditions, but I don't think "normally" specifies those conditions very well. --Bob K31416 (talk) 14:10, 26 November 2009 (UTC)

That is intentional, because the Scharnhorst effect (the reason why the "normally" is there) is somewhat obscure and explaining it in the text would be WP:UNDUE. (See /Archive 12 for discussion about that—it's scattered across several threads, sorry.) --___A. di M. 16:39, 26 November 2009 (UTC)

Although I didn't go prowling around archive 12, maybe it's not so bad. The text following "normally impossible" somewhat clarifies it. However, it might someday be improved upon. Regards, --Bob K31416 (talk) 19:50, 26 November 2009 (UTC)

I put your suggestion into the article, with a slight change in punctuation. --Bob K31416 (talk) 14:17, 26 November 2009 (UTC)

Suggested draft for rewrite of the fundamental role section

With most the trimming to this section done it is time to rewrite/reorganize what remains into as single coherent whole. I've taken the liberty of drafting a suggesting in my sandbox. The main thing I've tried to do is elucidate how the mention topic illustrate the central role c plays in physics. The whole piece should still more or less contain the same information as the trimmed section, but put a little more in context. The biggest change is that I've trimmed the whole one-way/two-way speed of light thing down to two sentences which are defer to a note. I found this to be a mostly technical point that is more about light then about c itself and was digressing the section. It needs to be mentioned though for those interested in this technical nuance, so a note seems warrented. The draft is not perfect, but I think it is a major improvement on the narrative structure.

Comments welcome. Also, please do not hesitate to copyedit/make improvements to the sandbox version. TimothyRias (talk) 10:56, 27 November 2009 (UTC)

Very good work. I think maybe we can somehow mention the Lorentz factor in the second paragraph (if it isn't too off-topic for Electron#Motion and energy, it definitely isn't off topic here); also "distant and almost simultaneous events" could be replaced with something more explicit, for example "events more distant than light would travel in the time elapsed between them", although I can't find a satisfactory wording for that right now. --___A. di M. 15:12, 27 November 2009 (UTC)

I propose inserting the draft into the article, since we seem to be agreeing that it is a step in the right direction. We can then work from there to smooth out some of the formulations. (TimothyRias (talk) 23:14, 27 November 2009 (UTC))

It's not clear to me that your major rewrite is an improvement. You mentioned, "The biggest change is that I've trimmed the whole one-way/two-way speed of light thing down to two sentences which are defer to a note." I would suggest that you make that edit in the article first (WP:BRD), so that it can be considered before we consider your other changes. --Bob K31416 (talk) 01:23, 28 November 2009 (UTC)

It is not possible to make that change without rewriting the first paragraph as well. (To let the note make sense.) It is not that hard to compare the draft text with the current text is it? If you have concerns about the new text it would be much more productive if you would just voice them. TimothyRias (talk) 09:31, 28 November 2009 (UTC)

Re "It is not possible to make that change without rewriting the first paragraph as well." - It doesn't seem that you need a rewrite of the first paragraph to trim the "two-way" part from it. Wouldn't the following strikeouts serve that purpose?

The speed of light has been shown experimentally to be independent of the motion of the source. It has also been confirmed by the Michelson–Morley experiment and other experiments that the two-way speed of light (for example from a source to a mirror and back again) in an inertial frame of reference is constant.

So I'll reiterate the suggestion in my last message. You mentioned, "The biggest change is that I've trimmed the whole one-way/two-way speed of light thing down to two sentences which are defer to a note." I would suggest that you make that edit in the article first (WP:BRD), so that it can be considered before we consider your other changes.

--Bob K31416 (talk) 15:54, 28 November 2009 (UTC)

TimothyRias, Apparently A. di M. just made an edit in the article[7] that seems to be a response for you to my above message. Is A. di M.'s edit what you would have done to satisfy the suggestion in my above message? --Bob K31416 (talk) 21:34, 28 November 2009 (UTC)

<outdent>I carefully considered the recent edit[8] that deleted the paragraph re measurement of c using clock synchrony, mirrors, etc. and felt it was not an improvement and reverted it. Although the paragraph may not be best placed in that section "Invariant speed in inertial frames", this problem of measuring the speed of light is very relevant to the topic of the speed of light and should be in the article. So I undid that edit. Finding the best place for it might involve reorganization of the article to have a section on measurement of the speed of light. It is somewhat surprising that the article isn't already organized in that way. --Bob K31416 (talk) 13:07, 29 November 2009 (UTC)

Note that the edit did not actually delete that paragraph but moved it to a footnote. At this point in the article a digression into synchronization of clocks is out of place, and is better deferred to a footnote. Reorganizing the article to have a section on measurement would be a good idea IMO, since that material is now oddly mixed into the history section. Distangling the two may involve quite a bit of work though. For the time being we cab keep the material in the footnote.

I'm going the implement the rest of the changes I proposed to the article since you apparently have no problems those. (TimothyRias (talk) 10:55, 30 November 2009 (UTC))

The burden is on the editor making a change to explain and justify a change to the article when it is questioned, especially when the change is as large as yours. Your explanation that, "The biggest change is that I've trimmed the whole one-way/two-way speed of light thing down to two sentences which are defer to a note" does not seem to be correct. Your version is a much more significant change than just trimming that one aspect. For one thing, your version seems to be a rambling of facts that aren't presented in a way that is as well organized into subsections as the previous version.

If you want to improve that section, I would suggest that you build on what is already there, with incremental changes. In that regard, and along the lines of my previous comments, I think the part regarding measurement of c and clock synchrony is better kept in the main text there, at least until a better place is found for it in the main text elsewhere, since it is very relevant to the topic Speed of light. --Bob K31416 (talk) 12:52, 30 November 2009 (UTC)

I take extreme offense at you calling the draft version of a rambling of facts. About saying that me description of the changes was incorrect, you completely ignore the first part of my explanation. The biggest change in content is moving the paragraph on synchronization to a note. All the other changes, are just reorganization of the facts already present in way that is coherent an explains how those facts are related to the subject matter at hand.

Note, also that I'm growing increasingly annoyed with your refusal to actually discuss the content of my edits, and instead only focus on how I'm make my edits. Note that there is no guideline that suggests that changes should be made incrementally. Nor is there a guideline saying that the burden is on the editor making the change. (Typically, the burden is on the person making the revert to explain why he is reverting.) Different editors have different editting styles and different ways of getting things done, so please stop acting like your way is the only way, and stop telling me what to do and what not to do. Instead, you might try responding in a constructive manner, and actually voice your opinion on changes when they are proposed. (TimothyRias (talk) 14:02, 30 November 2009 (UTC))

Tim, don't take offense at the confusion of others; just work to clear it up. I recommend the "move to note" as a first edit, and see if anyone objects; in another edit, just move paragraphs around. It will be much easier for others to see and understand what you've done if you break it up that way. Dicklyon (talk) 16:18, 30 November 2009 (UTC)

How hard is it for people to compare two 4-5 paragraph texts side by side? TimothyRias (talk) 16:33, 30 November 2009 (UTC)

Bob, I don't think your current approach of adding even more one paragraph/one sentence sections to the article is doing the article any good. It exacerbates the problem that the article does not explain how the verious subjects in the subsection are linked to each other (or the speed of light for that matter.) This is exactly the problem that my rewrite addressed. TimothyRias (talk) 15:24, 1 December 2009 (UTC)

I respectfully and strongly disagree and believe my recent changes, which were clearly shown in detail and accompanied with descriptive edit summaries, are a significant improvement to the article. --Bob K31416 (talk) 16:26, 1 December 2009 (UTC)

The trimmed section title aggravate that problem: I dare anyone reading a headline such as "Inertial frames" in the TOC to guess what the hell they're gonna read if they jump to that section. Also, discussing general relativity before special relativity feels definitely backwards to me. (BTW, could you use the "Preview" button before saving, rather than making several minor edits? That makes the "history" page harder to navigate, and reduces the probability of edit conflicts.) --___A. di M. 16:28, 1 December 2009 (UTC)

Re "discussing general relativity before special relativity feels definitely backwards to me" - I didn't understand this remark since special relativity is discussed before general relativity.

Re the other remark about the title, we apparently have a difference of opinion. --Bob K31416 (talk) 16:36, 1 December 2009 (UTC)

Huh? The section "Non-inertial frames", which discusses GR, comes before the section "Spacetime constant", which discusses SR. Also, I've seen that you've removed any connection between the experimental results of M.–M. and the theoretical basis of SR. The single most relevant fact about SR in an article about the speed of light, i.e. that SR is based on the assumption that c is constant and describes the consequences of such an assumption, is omitted. In TimothyRias's version that was crystal-clear, in yours they seem two mostly unrelated issues. --___A. di M. 16:45, 1 December 2009 (UTC)

I see your point and that could have been easily added to the section "Inertial frames" of my version, which relates to special relativity. Thanks. --Bob K31416 (talk) 17:15, 1 December 2009 (UTC)

Bob, I've reverted your changes, and I'll explain why. First of all, the current version of the Fundamental Role in Physics section is too sparse, and the addition of the subsections only makes matters worse. Second, you reverted a good faith edit, apparently on the grounds that the changes were too large, or that the editorial was too "rambling". I don't see that either was the case. To the contrary, the piece was rather well written, it presented the material in an interesting way, and it also managed to bring all of the major elements of the section together quite nicely. Making sure that the article has the proper flow is arguably more important than avoiding minor digressions. I certainly welcome your contributions, but I do ask that you please respect the input of the other editors as well. Cheers. Sebastian Garth (talk) 16:39, 1 December 2009 (UTC)

Well, it looks like it's 3-1 (TimothyRias, A. di M., and Sebastiangarth vs me) against my recent changes and for the changes of TimothyRias. So, unless there are other editors who agree with me, I'll abide by the current consensus, unless it changes. For reference, here's my version of the section "Fundamental Role in Physics" [9] which involved moving a part on clock synchrony and c of the old section to a new section elsewhere,[10] and here's TimothyRias's version[11] that was just reverted to by Sebastiangarth,[12] which also deleted the new section on clock synchrony and c. Regards, --Bob K31416 (talk) 16:45, 1 December 2009 (UTC)

When Sebastiangarth referred to "the current version of the Fundamental Role in Physics section is too sparse", I think he meant to refer to this version resulting from my edits of the old version. Note that each subsection has "See also" or "Main article" for noting the areas of physics that it pertains to and for getting more information. I thought that was a rather nice, informative, and organized style in the old version so I tried to follow it. Using subsections and "See also" was a nice way to show the topic areas in which the speed of light had a role. If there is some concern about subsection titles, that seems like something that could be easily worked out. But if everyone, including the other three editors in this discussion, prefers TimothyRias's version that is presently in the article, then that's the way it goes. --Bob K31416 (talk) 19:09, 1 December 2009 (UTC)