Wikipedia talk:WikiProject Physics/Archive August 2012

Cleanup and mentoring needed

A new user, Gdrg22 (talk · contribs), seems to be trying to contribute to relativity-related articles. Unfortunately right now that includes copy/pasting (or substing) the relativity sidebar into a couple of articles (Hawking radiation and Wormhole that I notice offhand). I've reverted these and left a polite note on their talk page explaining how curly-braces work.

They've also made nontrivial changes to many other articles, which I don't have time to vet at the moment but which could probably use scrutiny. At a glance, they've tweaked several relativity related articles, made adjustments to Template:General relativity to add names, removed material from nuclear fission (haven't checked what), and contributed quite a lot of talk page material to an AFC for an aether-based theory of gravity. --Christopher Thomas (talk) 22:05, 31 July 2012 (UTC)

I've looked through some of the edits, and found cause for worry. Gdrg22 seems to be removing articles from relevant categories without much consideration (and without giving edit summaries, which is also a problem). He seems to be targeting categories related to Jewish ethnicity, which is something of a red flag I think. Sławomir Biały (talk) 22:26, 31 July 2012 (UTC)

They're brand new, and haven't been following the usual patterns of outright disruption, so I'd be inclined to assume they're editing in good faith. They responded to my comments about transclusion, so it's probably possible to make them aware of other rules or editing norms they may be stepping on. --Christopher Thomas (talk) 00:37, 1 August 2012 (UTC)

I've been through most of the ethnicity edits. I reverted just a few of them, when there were sources or mention in the article. Most of the others, I didn't really have any opinion on. I have to admit that I don't really understand Jewish ethnicity categories. Sławomir Biały (talk) 00:47, 1 August 2012 (UTC)

It appears that this person changed the image for John Archibald Wheeler [1]. The new image does not resemble the old image. However I cannot verify either image as John Wheeler based on the sources for either image. Here is the first image: [2], and the second image: [3]. Also, I can't verify that the second image is indeed public domain. ---- Steve Quinn (talk) 02:45, 1 August 2012 (UTC)

The URL of the second image (from which it was downloaded) is http://elpais.com/ which appears to be a Spanish language online newspaper. I am guessing this is in their database somewhere. ---- Steve Quinn (talk) 03:15, 1 August 2012 (UTC)

Even if the new (much older) picture was published in 1923 (the last date allowed for its copyright notice), John Archibald Wheeler (born in 1911) would have been 12 years old at that time. Clearly the person in that picture is an adult, so it cannot be him. JRSpriggs (talk) 07:41, 1 August 2012 (UTC)

The second image is of "John P. Wheeler III, a decorated veteran who worked with three different Presidential administrations" (link). The first image looks like John-Archibald Wheeler, so it is probably him. This change needs reverting. CodeTheorist (talk) 08:12, 1 August 2012 (UTC).

Reversion done. CodeTheorist (talk) 08:20, 1 August 2012 (UTC)

On the other hand it might be J.A.Wheeler (link), but I think that it is better to use the old image given the doubt about the identity and copyright issues. CodeTheorist (talk) 08:31, 1 August 2012 (UTC)

FAZ has the same image here, so I think we can conclude it is J.A. Wheeler. BUT: that page says "(c) AP", which sounds very much unlike public domain. Gdrg22 has re-reverted to this image, again without any comment. I don't think we can keep the image. — HHHIPPO 16:31, 1 August 2012 (UTC)

There is a similar problem for Edward Arthur Milne with the image; it was removed due to disputed copyright, and then was reinstated by Gdrg22 without comment. CodeTheorist (talk) 17:02, 1 August 2012 (UTC)

Sanity check: Has anyone tried _talking_ to them and explaining the need for free-use images and why most images found online don't work for that? I don't see anything new on their talk page, and I'm not convinced that they'll be _reading_ edit summaries (given that they don't seem to write them). Explaining those to the new user would be handy too. --Christopher Thomas (talk) 21:43, 1 August 2012 (UTC)

For what it is worth, I can now confirm that the second photo is J.A.Wheeler (Emilio Segrè Visual Archives). The copyright status is still very uncertain. CodeTheorist (talk) 21:33, 1 August 2012 (UTC)

And it says date unknown. We may need someone who knows about the finer points of copyright vs. public domain in this instance. ---- Steve Quinn (talk) 22:15, 1 August 2012 (UTC)

OK. I just posted a request on Moonriddengirl's talk page to come and have a look. Copyright status is one of her specialties. ---- Steve Quinn (talk) 22:47, 1 August 2012 (UTC)

I left a message on Gdrg22's talk page, hope I got it right. Btw, the image date seems to be 1946. — HHHIPPO 23:23, 1 August 2012 (UTC)

Moonriddengirl replied on her talk page. She has assessed the situation and her reply will probably interest all participants in this thread. ---- Steve Quinn (talk) 23:07, 2 August 2012 (UTC)

By the way, in Template:General relativity... Millikan and De Pretto as major contributors to general relativity? And Lorentz? - DVdm (talk) 14:32, 3 August 2012 (UTC)

Some of those seem excessive. Certainly De Pretto should not be there. What are good criteria for the rest? I don't really think that Kerr, Friedman, Robertson, or Walker's bios are particularly important in the grand scheme of the subject. Sławomir Biały (talk) 14:48, 3 August 2012 (UTC)

I guess one (rather technical) criterion should be that they're listed in Contributors to general relativity, which has at least some kind of inclusion criterion. Once they're accepted there, one could say they can be promoted to the template if they made essential contributions to the core parts of general relativity, e.g. to what's described in Introduction to general relativity. One could also check if any of the similar templates around has some kind of inclusion criteria. — HHHIPPO 17:58, 3 August 2012 (UTC)

I think someone more knowledgeable in history of physics than me should have a close look at the recent activities of Gdrg22 (talk · contribs):

• he's adding a lot of people to sidebar templates, to the point where the question arises how many names are useful there,
• he's copied and pasted substantial text from George Sudarshan into History of Physics. Apart from questionable notability and NPOV, the uncommented copying smells like another copyright problem,
• he's removed mentions of Lise Meitner from Nuclear Fission and History of Physics.

Most of this is probably in good faith, but it could use some expert attention. — HHHIPPO 21:45, 4 August 2012 (UTC)

I just reverted an edit that inserted clearly wrong information. I would suggest that emphasizing WP:BURDEN when examining this user's edits could be beneficial for the quality of the articles in question. Regards, HaeB (talk) 04:01, 5 August 2012 (UTC)

Update: there seems to be a pattern here. Apart from adding tens of names to sidebar templates and some to articles, Gdrg22 in a number of cases also removed names from templates and articles, and did more or less subtle changes playing down the contribution of some scientists. The alarming pattern is: All of the scientists, who had their name removed or their role reduced, are Jewish. I don't want to jump to conclusions here, but I think this needs some explanation. P.S.: Sorry for calling Gdrg22 'he' earlier, should read 'they'. — HHHIPPO 10:57, 5 August 2012 (UTC)

Hello its seems a problem here , you forgot to mention that i added several jewish scientists that really contribuited with something new to the templates as perl in particle physics and lev landau when i noted this article about my suppose racism i was shocked, i was only trying to help , i noted a lot of scientists who are not reconized by the nobel commite and remove from the main template , i didnt notice but the coincidence are that most of them were jewish, and about lise meitner she helped to discover the nuclear fission but the real discover was otto hahn. i saw this in nobel prize offical site and articles in science , when i was doing my modifications i removed scientists that i consider not top to the there

thx for the attention and be careful when accusing people of racism — Preceding unsigned comment added by Gdrg22 (talk • contribs) 16:38, 5 August 2012 (UTC)

Dear Gdrg22, I explicitly didn't accuse you of racism, I only asked you to give some explanations to avoid the impression of a systematic bias. I'm sorry if that wasn't clear enough. This, this and this is why I didn't see that you used winning the Nobel price as an inclusion criterion. — HHHIPPO 16:54, 5 August 2012 (UTC)

Dear Gdrg22, whether intentional or not, there is the appearance of a pattern of de-emphasising Jewish scientists by removing their names or by removing the wiki linking from their names. This isn't helped by the fact that none of these changes have an edit comment, so that we are left guessing at your reasons. I've reverted three minor changes that you made, mainly because they had no edit comments and appeared to be part of a pattern. My apologies if I have misinterpreted your motives. CodeTheorist (talk) 17:04, 5 August 2012 (UTC)

brian shicmidt with Nicholas_B._Suntzeff (which is jewish) founded 'High-z Supernova Search Team' adam riess and the other get the credits from other jewish

chamberlain the leader maide the most contribuitions , i read this in a book 'segre'is the assistant - and i didnt know that he was jewish im not even entered his wiki page - and there are some controverses envolving him.

i exclude annon alan pezias name because it was already included in the introdution it was more for estetic and visual i felt strange i never seen a name which are not from the main person of the wiki page foccused. i wanted to deleted and just but later i gave up — Preceding unsigned comment added by Gdrg22 (talk • contribs) 17:08, 5 August 2012 (UTC)

about the V- A theory i know that two of the creators of eletroweak theory are jewish but one is muslim and the main boss "Abdus Salam" its unfair because it was an indian american who did it

and to make me clear im from brazil , i never met a jewish before , there are few jews in brazil and most of them live of the south im from north, it was only concidence, and i didnt know they were jews when i added lev landau and perl to templates

and for end the real discover of nucler fission was otto hahn not lise - which i didnt know was jewish

it might not be intentional but after this edebate when i knew that all scientists who were get overrated attention from others works were jewish it seems - an hipotetical- that a jewish included "lower level" scientists and excluded great scientists from the history , and one more thing there are lot of jews in quantum mechanics template and i didnt remove them because the nobel criteria , for me , in a especific field is not valid all contribuited

thx for attention — Preceding unsigned comment added by Gdrg22 (talk • contribs) 17:15, 5 August 2012 (UTC)

Re: Nicholas B. Suntzeff, you are correct that the supernova team was founded by Suntzeff and Brian Schmidt. However the mention of Adam Riess wasn't for the founding of the team, but was for the award of the Nobel prize, and half of the prize was awarded jointly to both Schmidt and Riess, so they both need to be mentioned. CodeTheorist (talk) 17:21, 5 August 2012 (UTC)

im ending my participation in wikipedia after all this "controversy", i dont want any kind of negative attention for me especially racism subject

thanks anyway — Preceding unsigned comment added by Gdrg22 (talk • contribs) 20:17, 5 August 2012 (UTC)

Dear Gdrg22. Well it's up to you, but thank you for your contributions some of which I thought were good changes.

To everyone else, perhaps we could review the following changes (some may already have been reverted, I haven't checked them all). These edits cause me some concern as they appear to be an attempt to de-emphasise certain physicists:

• Edits which de-emphasise Albert Einstein as a founder of modern physics: 1, 2, 3, 4
• Removed picture of Planck, Albert Einstein, Niels Bohr, de Broglie, Max Born, Dirac, Heisenberg, Wolfgang Pauli, Schrödinger, Richard Feynman: link
• Removed picture of Albert Einstein, Zeeman, Paul Ehrenfest: link
• Removal of mentions of Lise Meitner: 1, 2, 3
• Removal of Arno Allan Penzias, Yakov Zel'dovich, Vera Rubin from template: link
• Removal of Paul Ehrenfest, Eugene Wigner and David Bohm from template: link
• Removal of George Zweig from template: link
• Removal of mention of Jacob Bekenstein: link

Thanks. CodeTheorist (talk) 21:29, 5 August 2012 (UTC)

I think I checked all questionable removals now, and reverted most. Some of the templates still have a lot of people in the scientists list, but I see that's being worked on. I'm happy with my edits being reverted again, wherever there's a good reason. — HHHIPPO 21:59, 6 August 2012 (UTC)

"Supermassive Black Hole"

The usage of Supermassive Black Hole is under discussion, see Talk:Supermassive Black Hole (song) -- 76.65.131.160 (talk) 02:53, 1 August 2012 (UTC)

Nutation

I have a dispute with one ultramergist user of the type "let us expand the article to discuss a variety of applications of the word". This is not a complex case, it needs just a couple of experienced users to enforce certain well-known Wikipedia guidelines, see details. Incnis Mrsi (talk) 11:51, 5 August 2012 (UTC)

This has become a heated controversy. Some of the contributors have been flaming each other and it might be difficult to come to an agreement. Perhaps some cooler heads joining the current discussion would help to resolve the issue. RockMagnetist (talk) 20:26, 8 August 2012 (UTC)

Steam

Yet another "article about the term" but, unlike the topic just above, the case is quite interesting. Several users at talk: Steam tried to formulate a valid definition, to no avail.

To my opinion, "Steam" should not be an article, but probably a dab page, or maybe a redirect to vapor with a dab hatnote. Contrary to the current order on Steam (disambiguation), it should start with the most general sense, that steam means "vapor", a gaseous phase of matter, most usually water vapor. Then, steam engine is the most common application of the word (BTW it not necessarily uses a water vapor). Only after that should follow "steaming" and all items below. Incnis Mrsi (talk) 06:00, 6 August 2012 (UTC)

Accidently, I discovered yet another article: live steam. Awaiting for a cleanup of all this stuff, preferably by users with native English. Incnis Mrsi (talk) 08:56, 6 August 2012 (UTC)

Steam is not just water vapor; it is a region of air which is much hotter and much more humid than the surrounding air. I think that the distinction of the steam from its surrounding air is what is missing from the possible definitions being considered. JRSpriggs (talk) 15:37, 6 August 2012 (UTC)

Isidor Isaac Rabi

I've had Isidor Isaac Rabi nominated for GA since 8 June, and no takers so far. I have to travel overseas in a couple of weeks, so if anyone would like to have a go at reviewing the article, it would be very much appreciated. Hawkeye7 (talk) 21:45, 7 August 2012 (UTC)

Simple explanations, please

There is a regular problem throughout the science and mathematics articles in Wikipedia. It should be possible for someone doing their high-school homework to look up a subject and get a comprehensible explanation. A typical example is the article on Momentum, which starts with a vector equation. Although the present policy in WP is purist and technically impeccable, many articles on basic physics and applied mathematics are virtually useless for all but the cognescenti. Of course the heavyweight material can follow, but it should not be in the introduction or in the first few paragraphs until a simple, even if incomplete, explanation has been provided. JMcC (talk) 10:04, 22 July 2012 (UTC)

There is something about moving things which does not change. It depends on the direction in which they are moving. It can be passed from one thing to another, but the total of it cannot be increased or decreased. It is called (linear) momentum.

Is this the sort of lead you want? It does not sound encyclopedic. It sounds like an explanation for children. JRSpriggs (talk) 11:33, 22 July 2012 (UTC)

Articles are written for the intelligent but ignorant adult reader. We aren't trying to aim the content at children doing their homework. I think the lede at present is reasonable. IRWolfie- (talk) 11:40, 22 July 2012 (UTC)

There is a clear description on how technical articles should be written, see Wikipedia:Make technical articles understandable. Too many articles on mathematics and the physical sciences do not follow these guidelines. Does the average 'intelligent but ignorant adult reader' understand vectors before they understand the basics about momentum? Do not underestimate high-school children. The average child learning about physics will know probably more about the subject than the vast majority of the adult population to which this encyclopedia is aimed. Their existing knowledge will therefore be well beyond the 'intelligent but ignorant adult readers' who have probably forgotten much of what they learned at school. If we are aiming at this latter group, we have an even bigger mountain to climb. I commend IRWolfie for his even greater ambition for physics articles than mine. I accept that some articles on theoretical physics will not be readily accessible even to an average, intelligent and scientifically educated adult reader. However the basics of mathematics and the physical sciences should be clearly available. If you need a university degree to understand the intro on articles about basic physics, then we have got an article's accessibility all wrong. JMcC (talk) 14:13, 22 July 2012 (UTC)

I think, on the whole, that Jmcc150 is correct. A lot of articles could be made more accessible. For example, in Momentum, more could be said about the significance of the vectors. Since the lead has to summarize the content of the article, it would be inappropriate to begin with a 1-d tutorial; but if the history section were moved to the end of the article, the 1-d treatment would be the next thing after the lead. Also, more concepts like elastic and inelastic collisions could be summarized in the lead. RockMagnetist (talk) 14:45, 22 July 2012 (UTC)

Agree--We should not make articles sound dumb and pedantic, nor sacrifice accuracy for simplicity. But it is usually possible to write clearly and accessibly without those "crutches". I tried adding an intuitive example to the lead, maybe that will help a bit? Well, there is still certainly room for improvement!

JmcC: With few exceptions, people are actually trying to make science articles understandable. I know I am!! But it is very difficult, and it is not usually the first priority (usually behind accuracy, thoroughness, being understandable to practitioners, ...). So improving understandability does happen...in fits and starts, with many steps backwards as well as forwards. The point is, even though most of us agree with you, the problem will not be fixed overnight. You are being very helpful when you point out egregious cases, and even better when you propose some sentences, or an example, or a diagram, that helps you personally understand something. This can be the first step towards fixing the problem, one article at a time!! :-) --Steve (talk) 15:20, 22 July 2012 (UTC)

+1

Of the 14k+ articles covered by this project less than 100 are above B level. (Even for the Top priority articles only 10% is above B level). The rest still has a lot of improvements that need to be made. In most cases this includes improving the accessibility. However, improving accessibility costs a huge investment in time and effort from editors. So, doing this is going to take time.TR 16:14, 22 July 2012 (UTC)

I think that all articles should have the first introductory paragraph be an explanation in simple terms geared towards an average English-as-a-second-language or high-school-dropout reader. The rest of the introduction can be more complex, for the intelligent adult reader with a fair grasp of English. Anything requiring more than that in the section-0/introduction should be avoided. A more technical introduction can be given in a summary section, immediately following the introduction, for those readers who are subject literate. If the subject/topic is dense, then a full Introduction to X article might need to be built. But again, these introduction features should be there regardless of whether or not an Introduction article exists. (it might just direct people to the introduction article after the first simple paragraph, though) -- 76.65.131.160 (talk) 04:16, 23 July 2012 (UTC)

I've seen this type of statement come up again and again, and I'm going to make the same response (again): Some science topics can be made layman-accessible enough to explain to "high-school dropout" readers. Most can't. This is doubly-true for mathematics. If you attempt this for just about any high-level math topic, you'll wind up with "it's a type of thing" or "it's a thing that relates type A things and type B things". Literally, that's what you'll end up with. There's a reason people go to university for many years to learn some of these topics - most laymen won't even have a handle on the concepts they're based on, much less the article subjects themselves.

Physics isn't quite as bad, but it's closer that most people appreciate. Take refraction, for example. There are two or three (or more) levels of "this isn't how it works, but it's a simpler explanation" that people are taught before getting the real version. And that's for a concept that relates to something most people have experience with (light and the path light takes passing through things). These aren't exceptions - this is how most hard-science topics work. Scientists have spent several hundred years learning what exotic things other scientists have studied and pushing that boundary a little bit farther. Mathematicians have had even longer, and aren't constrained by having to wait for experiment results.

Lastly, you've mentioned "english as a second language", which suggests a focus on wording rather than content of the ledes. These are two different things. There's an alternate version of Wikipedia - the Simple English Wikipedia - that's meant exactly for the sort of situation you describe (keeping the complexity of concepts but trying to use a simplified subset of the English language).

In practice, I've found that excessive focus on either one of these harms articles. Keep them technically accurate first and foremost. By all means don't make them unnecessarily difficult for the layman, but a) hard concepts are there for a reason, and b) hard concepts are linked to their corresponding articles. That's the whole point of links in a wiki. If there's context that's needed in order to understand a concept, then all the reader has to do is click on the blue links for anything they aren't yet sure about.

The alternative is to have articles that present inaccurate material that harms understanding, and I don't consider that acceptable. --Christopher Thomas (talk) 05:46, 23 July 2012 (UTC)

It's a delicate and subtle matter to write an article that is both accessible and technically correct. The problem is, Wikipedia articles quickly drift away from such a finely balanced state because they are edited in a piecemeal fashion. In the best case, if enough knowledgeable editors are watching a page, they will fix any inaccuracies that creep in; but it's very difficult to preserve accessibility unless someone periodically does a rewrite (of at least the lead). Perhaps we just need to make sure those occasional rewrites actually happen? --Amble (talk) 06:33, 23 July 2012 (UTC)

I'm hearing a lot more pessimism about accessibility than is warranted. Writing for accessibility does not have to harm the article. Quite the reverse - it requires good writing and good organization. And if we govern our actions by what later editors might do, then we might as well stop writing GA and FA articles. I have been able to make Momentum more accessible by doing nothing more than moving stuff around, and much more could be done. I agree that not all articles can be made equally accessible, but an effort should be made. RockMagnetist (talk) 17:42, 23 July 2012 (UTC)

I agree that improvements in accessibility can often be made, and that this is worth doing. I've just seen way too many cases over the years where articles have been degraded due to accessibility being declared the top priority. It shouldn't be - accuracy should be (well, after "verifiability", of course). Generally this happens when people start waving around the "you should be able to explain it in terms anyone can understand" argument. Hence my strong reaction above. --Christopher Thomas (talk) 20:28, 23 July 2012 (UTC)

I think a problem is that many editors without much experience in a technical area think that making articles accessible is easy, or that basically anyone can do it, even those who do not thoroughly understand the field of study. But in actuality, it does require some expertise in the field, as well as writing ability and a significant investiment of time to do this in a way that actually results in an improvement. Sławomir Biały (talk) 20:58, 23 July 2012 (UTC)

You are misreading what I am saying. I did not say anything about most of the body of the article outside of section-0. The section following the introduction can be as dense and complex as need be. The introduction should not be exceedingly dense or complex. And ESL/HSdropout requirement for the first paragraph of the introduction is, I think, not unreasonable, so they can even understand what page they landed on. By selecting words available to those unfamiliar with English, allows both communities to read the first introduction paragraph. Making the form simpler as well, will allow younger readers and less intellectually able readers to know what page they ended up on. -- 76.65.131.160 (talk) 04:10, 24 July 2012 (UTC)

I am not misreading what you are saying. My point is that you can't give a meaningful summary for some topics. When you try, you wind up with pretty much literally "it's a type of thing" or "a thing that relates things", per above.

Tell me, how would you make the lede to gauge theory understandable to a high-school dropout, while still saying anything at all useful? Most theories of particle physics right now are gauge theories (or are approximated as gauge theories), so this is an important (and introductory!) topic. How would you write the lede for Lie group (the concept underpinning gauge theories)? How would you write the lede to Riemannian manifold? Spacetime is treated as a Riemannian manifold, so that's an important (and introductory!) topic for anyone who actually wants to work the math of general relativity.

I feel that you, and possibly others, are very seriously underestimating how much scientific topics depend on other scientific topics for context. Many physics articles and most math articles will need even more context (these are introductory topics!). --Christopher Thomas (talk) 04:43, 24 July 2012 (UTC)

There may come a point where it is impossible to make any wikipedia science article more understandable because we have run up against fundamental requirements of background knowledge. We are not there yet. Very few wikipedia articles are as understandable as they could be.

Let's take Riemannian manifold as an example. It could be improved by giving some examples of Riemannian manifolds, both familiar and unfamiliar (Euclidean space, surface of a sphere, spin(7)-manifold). There could be a picture illustrating "tangent space". There could be examples of things that are not Riemannian manifolds—spacetime, surface of a cube, etc.—and why they are not. Is the tangent space always equivalent to $\mathbb {R} ^{n}$? If yes, say so; if not, say that $\mathbb {R} ^{n}$ is one possibility and give an example of another possibility. All these suggestions apply to either the lede or an "introduction" section.

I suggest that when someone complains that an article cannot be understood by a high-school dropout, you can respond, "High-school-dropout might be too ambitious, but let's work on making it as understandable as possible." :-) --Steve (talk) 14:42, 24 July 2012 (UTC)

Typically, physics books are more accessible than mathematics books. Clearly the Yang–Baxter equation article is written from a mathematical point of view, making it completely useless (to understand this propely, you would likely already know a lot more about this topic than what is explained in the article). It is possible with some effort to write up this article in a way that makes it understandable to first year university students. In case of Lie groups, gauge theory it is the same story. The introduction of lecture notes on the application of Lie groups in physics that I studied from are perfectly understandable to 15 year old high schoolers. Gauge theory? Many modern QFT books have introductions that are accessible to high schoolers. And Paul Davies is able to explain this to complete lay persons, but then that may be too simplistic for us.

But if you remove some concept that is naturally rooted in some physical context and formulate it in an abstract mathematical way, you end up with an inaccessible math article. Count Iblis (talk) 16:49, 24 July 2012 (UTC)

Typically, physics books are more accessible than mathematics books. Unbridled subjectiveness cracks me up! I guess the reason I have shelves of math books I understand and only one physics book that explains things well is because I haven't found the right text. Or, more likely, physics texts, like mathematics texs, have a lot of cognitive conventions that require a lot of absorbing from multiple texts.

I am super interested in links to the introductory notes for application Lie groups in physics, and any other topics you mentioned that are accessible. Rschwieb (talk) 17:03, 24 July 2012 (UTC)

See e.g. these lecture notes. Count Iblis (talk) 15:37, 30 July 2012 (UTC)

Thank you! Rschwieb (talk) 18:21, 30 July 2012 (UTC)

I have waited a while, but the discussion seems to have petered out. I think we have agreement that it is unrealistic for an article on an advanced aspect of physics to be written for people who do not know the basics. However there are a group of basic articles that could be a point of entry for the layman. Momentum is one of these. We have to decide if a basic introduction is a separate article or is a replacement for the current intro that mentions vectors and relativity. I had a go at writing something and I will let you all decide whether that points to a separate article or a rethink on how we write introductions.

Momentum (plural momenta) is a measure used in classical physics to describe mass in motion. It is sometimes known as linear momentum or translational momentum.

All objects have mass; so if an object is moving, then it has momentum. The momentum of an object depends on how much mass is moving and its velocity. It is calculated using:

Momentum = mass • velocity

Because velocity is a speed in a specified direction, an object's momentum also has a direction as well as magnitude. Quantities that have both a magnitude and a direction are known as vector quantities. That is why there is a dot in the equation above, rather than a simple multiplication sign. Because momentum has a direction, it can be used to predict the resulting direction of objects after they collide, as well as their speeds.

Physicist use 'p' as the symbol for momentum, so the equation above can be rewritten as: p = m • v where m is the mass and v is the velocity. When using the SI system, its units are kilograms metres per second. For example a car with a mass of 1,000kg travelling at a speed of 30m/s westward would have a momentum of 30,000 kg.m/s

Don't pitch in to say I have got my physics wrong. This quite likely. This rough draft probably has all sorts of issues, but just view this as the level at which I would aim the intro (or a separate article. JMcC (talk) 11:47, 30 July 2012 (UTC).

Have you looked at Momentum recently? I have chosen to leave the lead as it is until I finish the body of the article, because the role of the lead is to summarize the contents. However, the introduction is similar to your proposal. Also, details like this should be discussed on the article's talk page. RockMagnetist (talk) 14:39, 30 July 2012 (UTC)

Sorry, I hadn't looked. It is much better. Thank you. Apologies for not putting this on the article's talk page, though the general principle of a clear introduction applies throughout the basic articles on physics. JMcC (talk) 18:29, 30 July 2012 (UTC)

To Jmcc150: You do not mention the fact that momentum is conserved. This is the crucial fact. The idea of momentum would be virtually worthless otherwise. After all, do you pay attention to random constructs like temperature times altitude? Conserved quantities are important because the conservation law allows us to make predictions about what might or might not happen. JRSpriggs (talk) 07:13, 31 July 2012 (UTC)

All of this is in the article. I suggest that anyone wanting to improve Momentum read the article and leave comments on its talk page. RockMagnetist (talk) 16:51, 31 July 2012 (UTC)

Yes, there are topics which would be nearly impossible to explain to non-experts, and there are particularly stupid people to whom it'd be nearly impossible to explain any advanced topics. But this effect is waaaaay overestimated; often the reason why people say something can't be explained in an accessible way is that they never seriously try to do that in the first place. (People said it would be impossible to make the lead of this more accessible, but a month later it looked like this.) As a rule of thumb, I'd say that if you've heard about a topic as an undergrad, then almost surely it's possible in principle to explain it in a way that an intelligent layman would reasonably understand. Refraction? FFS... When light passes from a medium to another, it changes direction. (That's why a pencil partly in water looks broken, and the way lenses work.) And the amount by which it changes direction can depend on the colour of the light; since white light is a mixture of light of different colours, you get rainbows. Even my grandma would understand this. The quantum mechanical mechanism by which that happens is more complicated, but I can't see why more than a short mention of it is needed in the lead section; the place to discuss it in detail is the body of the article. As for gauge theories, Lie groups, and Riemannian manifolds, I think I could explain them in a way that intelligent laymen could understand (at least the general ideas, though not the technical details), but that'd take more than a couple paragraphs so if we wanted to do that we'd need “Introduction to ...” articles. Now, explaining what a Ward–Takahashi identity is to my sister would be pretty much impossible, but the lead of that article would ideally be written in a way that someone reading it would understand that it's a mathematical identity useful in theoretical particle physics, and that they would need to understand quantum field theory to understand it. A. di M. (talk) 22:47, 31 July 2012 (UTC)

I heartily agree that it is possible for an expert who is also a good writer to make things clearer for a laymen. However, I think many experienced editors here are wary of other editors claiming to make something more accessible, when really they are introducing errors and oversimplifications. Introducing things in a clear way I think requires a fairly deep understanding of what's important and what isn't, as well as an ability to write clearly. Moreover, the goal of a lead isn't just to introduce the subject, but to provide an overview of the article—a capsule version of it. Often the goal of providing an accessible introduction and providing an overview are at odds with each other. Achieving the right balance is not easy. Instead, we often see editors (sometimes even experienced ones) churn out really dubious prose (example) in the name of making things easier for laymen to understand. I think we need a way of discouraging this kind of "improvement" while not stifling actual improvements to clarity. Sławomir Biały (talk) 22:57, 31 July 2012 (UTC)

Inexperienced editors can just as easily churn out dubious prose when they are adding obscure details. Saying that it is difficult to make articles understandable is just a cop-out. Experienced editors should lead the effort instead of looking askance at the efforts of the less experienced. RockMagnetist (talk) 23:39, 31 July 2012 (UTC)

I'm not copping out. I contribute where I can. But there are other, greater demands on my time than Wikipedia. I'm sure it's similar for many other experts in their fields who volunteer some of their time to contribute. It's important that we try to be realistic. It should be emphasized that making articles accessible is not easy. It is not something we want WP:RANDY to be doing, but it is the sort of thing that novices say "Well, I should be able to make this understandable for a non-expert, since I'm a non-expert." As someone with quite a bit of experience writing accessible leads to articles in technical areas, this sort of thing always seems to come up. Obviously, we should encourage our experts to do more, and our randys to do less. Sławomir Biały (talk) 00:24, 1 August 2012 (UTC)

It sounds like we're really coming at the same answer from different directions. But so many words have been going into discussing whether articles can be made accessible rather than how we can encourage good editors to do it (the subject of the subsection I started). RockMagnetist (talk) 02:28, 1 August 2012 (UTC)

One more point: For every example where someone tries a naive simplification of the material, I see ten where they try to pack a complete definition of the subject into the first sentence (Inertial frame of reference, for example; see also this discussion). RockMagnetist (talk) 02:36, 1 August 2012 (UTC)

Ideas for promoting accessibility

I think it is important to make physics articles accessible to as broad an audience as possible. Several ideas have come out of the recent CfD on Category:Introductory physics that might be worth pursuing. These include new articles (Introduction to physics and List of introductory physics topics). There are also administrative aids like Wikipedia:WikiProject Mathematics/Wikipedia_1.0/Basics, membership in which is triggered by a field in the {{maths rating}} template. Maybe even a working group on introductory physics could be justified. RockMagnetist (talk) 15:54, 22 July 2012 (UTC)

I think we should categorize introduction articles as well, say Category:Introduction to physics (and List of introductions to physics topics), instead of "introductory physics", since while a topic may be an introductory topic, it can also be a more advanced topic. Afterall, we have basic aerodynamics as part of pilots courses, so an introductory physics topic. But aerodynamics is an advanced applied physics topic generating much research in the world today. (note the difference between "introduction to" and "introductory". A topic treated in introductory instruction for physics can be treated in advanced instruction and in research, while an introduction to that topic is only introductory.)-- 76.65.131.160 (talk) 04:21, 24 July 2012 (UTC)

Categorizing by the type of article (such as introductory articles) is not recommended in the guidelines for categorization. However, the administration category Category:Introduction articles exists and can be populated using {{Introductory article}}. The physics introduction articles are already in it. RockMagnetist (talk) 22:31, 24 July 2012 (UTC)

I thought the idea of an introductory wikibook sounded like a good idea. IRWolfie- (talk) 14:46, 24 July 2012 (UTC)

It appears that the category Wikipedia:WikiProject Mathematics/Wikipedia_1.0/Basics is not used any more. There is no reference to it on the wikiproject main page or in recent discussions. There is also Wikipedia:WikiProject General Audience, which has been inactive for some time. Apparently these approaches don't work. RockMagnetist (talk) 23:30, 31 July 2012 (UTC)

I have created List of physics concepts in pre-college curricula, and one lesson I learned from doing it is that it is much easier to do a good job of a list than a category. I basically translated the California high school physics standards into a list. RockMagnetist (talk) 22:15, 24 July 2012 (UTC)

off topic

I smiled when I read what User:Christopher Thomas says above: If you attempt this for just about any high-level math topic, you'll wind up with "it's a type of thing" or "it's a thing that relates type A things and type B things". Literally, that's what you'll end up with. Christopher is perhaps unwittingly using the language of category theory, talking about objects and arrows. Perhaps we should be teaching category theory to grade-school children. The children would understand, but sadly, the parents would have the teacher's head on a pike by the end of the month, and so here we are... linas (talk) 03:29, 18 August 2012 (UTC)

Something similar was tried. It was called "New Math", and was a spectacular failure.

My point, above, is most of the articles in Category:Physics and almost all of the articles in Category:Mathematics discuss concepts that are only meaningful in terms of other "advanced" concepts, and so forth (turtles all the way down, to borrow a phrase). The stack isn't infinitely deep, and I agree that such articles shouldn't be made unduly complicated or opaque, but to expect a reader (in high school or out) without any of that context to understand such a topic is silly. Better to have the lede point people at the concepts they'll need in order to understand this one, so that they can gain that context.

To butcher another quote: Make these articles as simple and clear as possible, but no simpler. --Christopher Thomas (talk) 03:56, 18 August 2012 (UTC)

Nuclear Physics Laboratory

I am wondering if people are aware that Nuclear Physics Laboratory is a redirect to Denys Wilkinson Building. Although it seems to serve as a proper name, I think this is useful as a general description or a disambiguation page (if it is needed). ---- Steve Quinn (talk) 19:02, 7 August 2012 (UTC)

A disambiguation page would be better -- 70.24.247.242 (talk) 05:27, 12 August 2012 (UTC)

Position space, position vector, momentum space, reciprocal lattice...

What to do about the stubby Position space (r-space)? Add material or merge?

One possibility is the rewritten (by me) position (vector) article, which links to and describes position space.

A better place (I'd be inclined) is to merge into momentum space (k-space) since this already contains info on k and r as the spatial analogue to angular frequency ω and time t, and that functions of r can be Fourier transformed into functions of k and vice versa because of the space-inverse space relation. It can and should be extended to 3d though... If so, what would the best title be for the merged article: "position-momentum space", or "position and momentum spaces" (obviously with the separate articles as redirects)?

By all means closely related articles like reciprocal lattice, phase space, configuration space should be left alone, but position space needs to go somewhere...

What do others think? Thanks in advance for any/all help. Maschen (talk) 07:07, 16 August 2012 (UTC)

I should add: I'm in the process of upgrading the momentum space article a little. There are no sources, I can add some but will have to look for more later. If people can add refs please do so. Maschen (talk) 07:17, 16 August 2012 (UTC)

I think there may be a good case to be made for a joint article: position and momentum space. The two terms draw their relevance from their relationship (and contrast) to each other. Since it is pretty much impossible to explain the one without the other, you might as well do the explaining together.TR 09:13, 16 August 2012 (UTC)

Exactly! Maschen (talk) 09:34, 16 August 2012 (UTC)

I agree about position and momentum space.

There is a lot to say about k-space in crystals that is different from k-space in vacuum: Things like reciprocal lattice, Brillouin zones, etc. etc. The reciprocal lattice article already has all that. Although it would be nice to have an article with the title k-space (crystals) or something like that, I don't think it's particularly necessary. I think the status quo is that reciprocal lattice is the "headquarters" for all information about k-space in crystals, and that's fine with me. I added a little section into momentum space to help cement that situation into place.

I think position vector is fine as is and should stay separate. --Steve (talk) 13:49, 16 August 2012 (UTC)

Position and momentum space is intended for the more mathematical side to k-space (Fourier transforms of r-space functions, operators, reciprocal vectors etc.), though some inevitable applications to condensed matter physics can be included. Quantum mechanics happens to be in momentum space for physical analogy. I agree reciprocal lattice should be a separate article. Maschen (talk) 13:57, 16 August 2012 (UTC)

No point in waiting around, given the clear consensus to unify them into the same article. Here goes... Maschen (talk) 21:20, 16 August 2012 (UTC)

Ok - it's a start. Others are welcome if they have anything to add. Maschen (talk) 22:07, 16 August 2012 (UTC)

Looks like a good start! RockMagnetist (talk) 23:01, 17 August 2012 (UTC)

Thank you. Maschen (talk) 23:30, 17 August 2012 (UTC)

It would have been nicer to move the old article to the new name, instead of doing a cut n paste n delete of content; a move would have preserved both the edit history and the talk page... Next time, please move, instead of cut-n-pasting.

Also: should mention e.g. that its all a special case of pontryagin duality, as this opens the door to many othter concepts in physics. linas (talk) 01:53, 18 August 2012 (UTC)

I know - I realized that after, which is stupid of me. It will not happen again. Maschen (talk) 03:08, 18 August 2012 (UTC)

Momentum operator "makes no sense"...

In the recent spirits of improving momentum-related articles, an editor has tagged this article as "too technical", another says it makes no sense mathematically (see talk:momentum operator#Definition). I'm not sure how much more accessible to make it. Opinions? If others can then feel free. Maschen (talk) 23:30, 17 August 2012 (UTC)

It might be a good idea to consider the same questions for some of the other operator articles, for example Position operator, Energy operator, Rotation operator (quantum mechanics) - or any of the other pages linked by Template:Physics operator. RockMagnetist (talk) 23:41, 17 August 2012 (UTC)

Very true. Position operator seems to be overdone: the lead statement should just be $\mathbf {\hat {r}} =\mathbf {r}$, with some illumination on the connection to the momentum operator in the Uncertainty principle and in position and momentum space etc. following after, currently it's not very readable... Not sure how to improve rotation operator either though... Maschen (talk) 23:50, 17 August 2012 (UTC)

The statement $\mathbf {\hat {r}} =\mathbf {r}$ is not correct. In fact r is the eigenvalue of $\mathbf {\hat {r}}$. Xxanthippe (talk) 00:12, 18 August 2012 (UTC).

Yes I know r is the eigenvalue, but the position operator is a multiplicative operator in position space and $\mathbf {\hat {r}} =i\hbar \partial /\partial \mathbf {p}$ in momentum space isn't it? How else can you define the angular momentum operator as $\mathbf {\hat {L}} =-i\hbar \mathbf {r} \times \nabla$ in position space? (by all means a definition in terms of generators is more fundamental...). Maschen (talk) 00:28, 18 August 2012 (UTC)

I think the most glaring omission in Momentum operator is - what is it taking a derivative of? The whole concept of a wave function is missing. RockMagnetist (talk) 23:56, 17 August 2012 (UTC)

At the beginning of the article it says "In quantum mechanics, momentum is defined as an operator on the wave function." and there is the section momentum operator#De Broglie plane waves which is all about the wavefunction for a plane wave? Maschen (talk) 23:59, 17 August 2012 (UTC)

I didn't notice it was mentioned in the lead, probably because it is such a terse statement. I think the wave function needs to be described in more detail in the introduction, immediately before defining the operator. RockMagnetist (talk) 01:29, 18 August 2012 (UTC)

First try ok, immediately onto the eigenvalue and QM measurement from the wavefunction? Maschen (talk) 01:44, 18 August 2012 (UTC)

Yeah, I think the issue raised on the talk page is that neither the domain nor the codomain are specified. Are these bounded functions? square-integrable functions? using what measure? does it require uniform convergence? or any convergence at all? The momentum operator is not a bounded operator, its not trace class, which means it has discontinuities, as typical in Frechet space, and etc. So, yeah, the article really does "make no sense" at all, although the sloppy presentation given is not atypical of an undergrad physics textbook treatment, which sweeps all such details under the rug. We do a dis-service by ignoring such details. linas (talk) 02:01, 18 August 2012 (UTC)

The other thing I find incredibly annoying about such articles is the utter lack of historical context. This is an operator that Bohr and Sommerfeld vaguely though about in 1910 or 1920 or whenever, and Schrodinger, and Wigner, and many others fully elucidated a while later. I wish the history were there... linas (talk) 02:08, 18 August 2012 (UTC)

I tried to clear up some more according to RockMagnetist's suggestions. I apologize if it’s no good, and agree with what you're saying also (but don't fully understand the fine details about boundedness/convergence/codomains etc. and can only leave these to those who are inclined and qualified)... Maschen (talk) 02:12, 18 August 2012 (UTC)

Hmm. Every function (mathematics) has a domain and a codomain: the "from" space and the "to" space that a function maps between. In quantum mechanics, these are often the square integrable functions on flat Euclidean space, i.e. some Hilbert space. More generally, they may be from any normed vector space, e.g. Banach space carrying an Lp norm. A requirement of uniform convergence is often made. A bounded operator is one whose eigenvalues are bounded. These should be all be factoids available to undergrads paying attention in class ... maybe making a guest appearance on quizzes and exams...? From the physics point of view, there is also the 4-momentum and the Dirac slash which this article should mention. linas (talk) 02:32, 18 August 2012 (UTC)

Ok - I know what domain, codomain, series convergence, and square integrable functions, norms, Dirac slash/Feynman notation are, but enough on Hilbert/Banach/Frechet spaces/operator theory... Which is why I don't want to write about those latter bits because it'll end up wrong which is just pointless, it'll result in a mess to clean up. Maschen (talk) 02:40, 18 August 2012 (UTC)

SHIKES I should have said I did NOT know enough on Hilbert/Banach/Frechet spaces/operator theory!!... Sorry to disappoint. Anyway the Dirac slash has been inserted. Maschen (talk) 03:08, 18 August 2012 (UTC)

Very interesting... so the article on bounded operator gives as an example the Laplace operator, which is bounded on Sobolev space. Very interesting... Well, of course, the Laplace operator is just the energy, its just the square of the momentum. Now, in physics, the energy is unbounded: you can have arbitrarily large values of energy (and arbitrarily large momentum) so these operators are not bounded on the usual spaces of physics/quantum mechanics: i.e. they are not bounded (and thus, not continuous) on the usual Hilbert space of square integrable functions. But Sobolev adds a trick: he defines the "length" or "size" or "norm" of a wave function to be larger when it has a higher energy. So, boundedness, or not, depends on the domain of the operator... must re-read Sobolev space again ... hmm .. and, of course, the eigenvalues of the momentum and energy operators on a Sobolev space no longer correspond to the physical momentum and energy. Curious. linas (talk) 02:45, 18 August 2012 (UTC)

A little better to say the boundedness of the operator depends on the topology of the space being acted on. The Sobolev spaces H_s have a different Hilbert norm; roughly it is the sum of the L^2 norms of a function and its (distributional) derivatives up to say order s. So by design differentiation is a norm decreasing linear operator from H_s to H_s-1. Equivalently, taking the Fourier transform this means we have the multiplication by r operator who domain is L² functions f such that r^sf(r) still lies in L². The spectrum of this operator would be in the closed unit disk; I am not sure how "physical" that is.

Another non-Banach example where differentiation is continuous would be the Schwartz class (which is dense in L²). Here again this is by blatant design, the derivatives are used to define the seminorms. Mct mht (talk) 04:11, 18 August 2012 (UTC)

Thank you. I think this nicely illustrates the point about "confusion" I'm trying to make below. In physics, the norm is "God given", since it can be measured in the lab as a probability. When this norm is used, then the eigenvalues of the momentum operator are physical momenta. Failure to use the correct norm means you get "non-physical" results (such as eigenvalues lying within a circle). For this article, it is probably sufficient to say that the norm demanded by physics is that of square-integrable functions. (In fact, for quantum mechanics, this is actually not quite correct; it appears that quantum is, more accurately, something that happens on complex projective space. To see this, one needs to look at the holonomy arising from classical electrodynamics for the Bohm-Aharonov effect-- its a U(1) line bundle.)linas (talk) 04:40, 18 August 2012 (UTC)

Would it not be desirable to mention that the wave function can be approximated by

$\psi \approx A\exp {\frac {iS}{\hbar }}\,$

where A is a normalization constant and S is Hamilton's principal function. I just realized that this formula, which I had long assumed was correct, is wrong because it has the wrong variables. While S is a function of both the qs and the ps (and t), ψ is a function of either the qs or the ps but not both. Any ideas on how to fix it? I see that I should read the articles to which I am linking before linking them. JRSpriggs (talk) 04:45, 18 August 2012 (UTC)

Yeah, you are thinking of the functional integral of quantum field theory, which does have a peak at the classical action (physics). So, in a hand-wavy sense, your formula is almost right, but its a little more subtle than that. (One interesting trick is to expand the functional integral in powers of h-bar, and then I think terms like yours show up, or thereabouts. Its not exactly trivial). linas (talk) 05:00, 18 August 2012 (UTC)

I would like to remind everyone of some tenets of Make technical articles understandable: 1. Put the most understandable part of the article up front; 2. Write one level down; 3. Add a concrete example. Maschen has made a start on that and I commend him for it.

When faced with an article on basic physics like this, I ask "What would Feynman do?" The answer is, Feynman begins by saying "performing an operation on one state produces another state." He manages to say quite a lot without worrying about what domain the states are in.

Details about the choice of (co)domain should certainly be in Operator (physics), but it's not obvious that it should be repeated in every article about particular operators. The choice is not unique, as Linas demonstrated. A physicist would tend to put the operators in Hilbert space, but a mathematician may prefer a more general vector space. Thus, it may distract from a discussion of the momentum operator itself. RockMagnetist (talk) 04:02, 18 August 2012 (UTC)

OK, I sort of got carried away, and yet, no.... Yes, cradling a copy of the Feynmann lectures while editing this article is a very good idea. And, yes, at the start, at it's core, the article should focus primarily on the physics aspects. Yet, as I learned the hard way (the very very hard way, actually), brushing the details under the rug can lead to both over-confidence, and, someday, a crisis of confusion. It doesn't take too much to learn Fourier transforms and bra-ket notation and become confident in writing and manipulating things like <p|x>. Sadly, this can all fall apart and go all horribly wrong when one tries to take these insights into other areas which look superficially similar. Equations that "should have worked" become nonsense, and it can take a while (took me a long while) to understand that the nit-picky, detailed definitions that mathematicians insist on can be the difference between something that works and a result like 2+2=5. Thus, deeper in the article, it should at least attempt what the position operator article does: it defines the domain of the operator. It talks about measurement and norms. It actually could say a lot more, but its a start. And so something vaguely similar here is not only appropriate, but should be required. linas (talk) 04:09, 18 August 2012 (UTC)

It sounds like you would be a good choice to write that part of the article. It would be interesting to see examples where rigor is needed. RockMagnetist (talk) 04:22, 18 August 2012 (UTC)

Calling my bluff, eh? Easier said than done; the explicit examples I know of are all one-off, coming from dissipative systems and the like. But as mentioned above, for this article, if you simply use the Sobolev space for the domain of the momentum operator, instead of Hilbert space, you get a perfectly valid operator, which, notationally written looks identical to that given in the article. However, the Sobolev norm is not the square of the wave function, and is thus not the probability, and the eigenvalues are not the physical eigenvalues (as they now all lie within the unit circle). So you still have what looks to be the same operator, with what seems to be almost the same eigenfunctions, but the results are unphysical. linas (talk) 04:52, 18 August 2012 (UTC)

I've probably wasted too many electrons here already, but here's another example: the time evolution of an undisturbed quantum mechanical system is given by a unitary operator (by exp(iHt) to be precise, H the Hamiltonian). The eigenvalues of a unitary operator all lie on the unit circle. However, bump the system, force decoherence, or a quantum measurement, you stop the unitary evolution, you get a dissipative system. The eigenvalues are knocked inside the unit circle; time is no longer reversible (backwards time would mean eigenvalues lie outside the circle; running time backwards would explode the system). One way to understand this is that when you force decoherence, you are no longer using the usual square-integrable wave functions of QM, you are using a different space that models (for example) a thermal bath (or whatever). The details depend on the journal, the author and the decade in which the article was written. linas (talk) 05:46, 18 August 2012 (UTC)

Torricelli's Equation?

I hardly think this is actually a worthwhile "article". It has zero sources, and is just one of the "suvat" equations with an elaborate derivation.

Maybe this can be merged into the section Equations of motion, Constant linear acceleration: mentioning one of the suvat equations was also found (and not "created") by Torricelli?

This has already been suggested here way back in 2005, to no effect... Maschen (talk) 14:53, 16 August 2012 (UTC)

Well, I think the whole thing is of some historical interest and significance; unfortunately, that is not how the article is currently written. The "derivation" should be scrapped, and replaced by historical context: how was the equation found? what did Newton have to say about it? Did it enter the vis-viva controversy, and how? (it surely must have!) For these reasons, I don't think it should be merged, but let it await some kind of historical expansion...linas (talk) 22:35, 17 August 2012 (UTC)

If historical sources aren't presented, can I suggest that this might belong better in the conservation of energy article, as a fairly accessible example of it? Sławomir Biały (talk) 22:45, 17 August 2012 (UTC)

Ok - both points are very true. Let's indicate this on Talk:Torricelli's equation and see what happens (I don't have references btw). Maschen (talk) 23:30, 17 August 2012 (UTC)

Based on personal experience with WP, it may take 5 or 10 years for the desired content to show up. I see no harm in leaving the article as it currently stands, its not getting in the way of anything: its not like every stub has to be merged somewhere. linas (talk) 02:14, 18 August 2012 (UTC)

Speaking of vis viva, is there a misplaced claim about conservation of momentum? See Talk:Vis viva. --Amble (talk) 04:32, 20 August 2012 (UTC)

Magnetic monopole and Yang-Mills theory

Please see here. The magnetic monopoles#appendix section has been copied from this site. Ideally it should be rewritten, although I don't understand Yang-Mills theory so can't do much about that... sorry. Maschen (talk) 12:17, 18 August 2012 (UTC)

The SpringerEOM license allows copying but requires attribution, and so this kind of copying should include a note along the lines of "tis article contains material from Springer EOM, licensed under the CC-by-SA and GFDL..etc." I'm looking to see if we have a template for springer that automatically does this...(we do have one, e.g. for planet math) here Template:PlanetMath attribution we need one for springer ...linas (talk) 14:09, 18 August 2012 (UTC)

Now see Template:SpringerEOM attribution linas (talk) 15:21, 18 August 2012 (UTC)

Excellent - thanks for doing all this. Maschen (talk) 21:34, 18 August 2012 (UTC)

Electric torque?

This is a pointless "article": three sentences about the torque exerted on water molecule dipoles in food due to microwave radiation in a microwave oven. It doesn't even get the terminology right: "electric torque is the force heating water in the microwave oven". It should be just blanked, redirected, perhaps mentioned in the electric dipole moment article. Maschen (talk) 11:36, 21 August 2012 (UTC)

We already have an article on dielectric heating, which covers the same physics. Redirected. --Amble (talk) 15:02, 21 August 2012 (UTC)

Thanks - I missed that article. Maschen (talk) 15:10, 21 August 2012 (UTC)

Isospin-1 photon... what?

The photon article states that the isospin of a photon can be either 0 or 1. I thought this was clearly nonsense, but the PDG does list the photon has having either isospin 0 or 1, which is making me question a whole lot of things about what I know about isospin. This post on physics.stackexchange.com seems to say that the PDG is somehow referring to weak isospin, but why in the world would they recycle the I symbol for that when everywhere else it means normal isospin? Can anyone make any sense of this? Headbomb {talk / contribs / physics / books} 15:33, 18 August 2012 (UTC)

Yeah, that sucks. The article should be clarified. In the standard model, and specifically the electroweak subsection of it, the photon appears in a triplet with the W and Z bosons. The Higgs symmetry breaking gives W and Z a mass, but leaves the photon massless. The "weak" isospin refers to the weak force. The recycling of symbols of unfortunate... The bit about isospin 0 or 1 ... I don't remember any more, but perhaps this is the Cabibo angle business, which screws over the mass eigenstates vs. the isospin eigenstates (so that the Z boson is also a superposition of spin 0 and 1, but orthogonal to photon.) Yeah, see weak isospin and especially weak hypercharge for details.) linas (talk) 17:37, 18 August 2012 (UTC)

You mean Weinberg angle not Cabibbo angle. — A. di M.  18:15, 18 August 2012 (UTC)

Yeah, just as I went to fix that, a thunderstorm set in and I lost internet :-) anyway, the electroweak article spells it all out in some detail. linas (talk) 18:30, 18 August 2012 (UTC)

To be clear, the choice of word "isospin" for "weak isospin" is a historical accident/convenience. It simply refers to the idea that there is an SU(2) symmetry in there. Count yourself lucky that its not the word used for all occurances of SU(2) symmetry. of course, integer spin means a triplet or adjoint representation, and half-integer is a doublet or fundamental representation of SU(2) — Preceding unsigned comment added by Linas (talk • contribs) 17:54, 18 August 2012 (UTC)

They used I because the other choice, T, is ambiguous too. Surely it is the weak isospin what the photon may have, not nuclear isospin. But what means an enigmatic notation I = 0,1? There are more thoughts about this. BTW, does I mean I₃ or what? Incnis Mrsi (talk) 18:07, 18 August 2012 (UTC)

Properly speaking, I is a vector operator, with components I_x, I_y and I_z or I_1, I_2 I_3 depending on author. But equally often, it also means the ... um, representation err.. index (the Casimir invariant), of the vector operator so that its integer or half-integer, just like for spin. Thus, the operator I^2 has eigenvalues I(I+1) just like usual. All of this is "generally understood" without explanation; it follows from a general understanding of su(2) which is de rigeur for physics in general. Similarly, the statement that I=0,1 is really a shorthand for the Weinberg angle, and you are supposed to "just know this". Here, in WP, we should clarify at least the last point; we should not have to explain the first part, which follows from a general knowledge of su(2).linas (talk) 18:38, 18 August 2012 (UTC)

Or to be even more precise: the symmetry of electroweak is su(2) x u(1). The weak bosons are in a triplet of su(2) and so have I=1 and I_3 of +1, 0 and -1. There's another thing, called "B" that is an su(2) singlet, with I=0 and I_3=0 It mixes with the I=1, I_3=0 thing to give us the photon and the Z. The electroweak article mostly says this, but it could spell it out in slightly better detail, I think. (Its not terribly hard, once you understand it) linas (talk) 18:49, 18 August 2012 (UTC)

Sorry for posting here so much, but.... those articles also fail to state that the weinberg angle (and the cabbibo angles) are purely experimentally determined. There is no theory that explains what these values should be. (well, I suppose some supersymmetry or string theory attempts to give them a value, maybe... but its an open question) I find this quite remarkable. It really means that we are still waiting for some sharp pencil to explain why these are what they are, presumably garnering a Nobel prize in the process. linas (talk) 19:02, 18 August 2012 (UTC)

Ok so to recap, and make sure I understand things, the strong interaction-related isospin due to the up/down quarks (which I'll call I^ud) of photons is indeed zero, but some other SU(2) symmetry, the weak interaction-related isospin (which I'll call I^W), can be either 0 or 1 (or a mix of 0 and 1?). That is when the PDG writes I(J^P) of say mesons [4], they really mean I^ud(J^P), but when they write the I(J^P) of photons [5] and possibly gluons [6], they really mean I^W(J^P)? Because if so, the PDG should really come up with better symbol use, or make it abundantly clear what I is exactly referring to. Headbomb {talk / contribs / physics / books} 21:53, 18 August 2012 (UTC)

Uhh, no. These are all exactly the same isospin, the weak isospin. There are a whole mess of weak isospin doublets in the standard model: (electron, electrons neutrino) and (u,d) for lowest energy flavors. There are four more doublets for the next set of flavors. These all couple to the su(2) x u(1) gauge field exactly the same way. This gauge field has one vector, and one scalar. The vector is called W, the scalar is called B. The vector W is written as the usual lie algebra: $W^{+}=W_{1}+iW_{2}$ and $W^{-}=W_{1}-iW_{2}$ and $W^{0}=W_{3}$ all of these have weak isospin=1, and the I_3 component is +1, -1 and 0, respectively. The singlet B has I=0 and I_3=0. Now, its impossible that W+ and W- could mix with each other, or with W^0, so they don't. It would be insane to suggest that they could, it defies the logic of su(2), it defies the whole point of having a vector. However, there is no mathematical reason why W^0 and B can't mix, and ... lo and behold, they do. The mass eigenstates are not the same as the isospin eignestates. Just a fact of life, the standard model does not offer any prediction in this regard, one way or the other. No one knows why they mix (why the mas and isospin eigenstates aren't the same) or can explain it. We can explain *how* they mix, this is the Weinberg angle. But why .. big mystery beyond the standard model. The photon and the Z^0 both have I_3=0. Equally irritating, the quarks mix too: the mass eigenstates of the quarks are not the weak isospin eigenstates of the quarks. So, for example, there is an up quark which has a mass, and it is a mix of the weak-quark-up, weak-quark-down, weak-quark-strange, etc. This insane mixture is given by the Cabibbo angles. So you really should be thinking of two different kinds of quarks: those that are weak-isospin eigenstates, and those that are mass eigenstates. They are not the same.

OK so what the heck is the strong isospin? It is the isospin for the MASS eigenstates! If you visualize the weak isospin operator as a 3D vector, pointing in some direction (say, true north), then the strong isospin vector is pointing in some other direction (say, magnetic north). The difference between these two directions is the Cabibbo angles. Again, why the heck these two damn things point in different directions .. is utterly unknown. They just do. However, they are, in this sense, "exactly the same thing", the one and the same isospin, but measured in two different coordinate frames: either the coordinate frame of the mass eigenstates, or the coordinate frame of su(2)xu(1) weak gauge symmetry.

To use a formula I just made up on the spot, we have

${\vec {I}}^{strong}=M{\vec {I}}^{weak}$

where M is (related to!?) the Cabibbo matrix, and the quark mass eigenstates are eigenstates of I^strong while the quark weak eigenstates of I^weak. M really is supposed to be an ordinary rotation matrix, and experimental results seem to agree. I'm glossing over something here, and that is the 3 flavor generations, so the above formula is actually kind-of wrong. So its a little more subtle than that, but not much. At the pop-sci level, its more-or-less correct-ish. Does it all make sense now? linas (talk) 04:00, 19 August 2012 (UTC)

No, in the hadron tables by I they mean the ‘original’ isospin (which together with the strangeness indexes the members of representations of the approximate flavour SU(3)): they list the Ω⁻ baryon as having I = 0 (its weak isospin is −3/2). (Also, the CKM matrix only mixes quarks with the same electric charge.) — A. di M.  09:17, 19 August 2012 (UTC)

The answer why the neutral gauge bosons, the quarks, (and the leptons) mix is really simple: Because they can. Naturalness (physics) requires that all terms that are allowed by symmetry and renormalisation are present in the Lagrangian. The mixing terms are allowed therefore they are non-zero. Now, if these mixing terms were zero, then that would require an explanation! Of course, a valid question is why is there a hypercharge symmetry at all. (We know there is because we see 4 gauge bosons).TR 09:40, 19 August 2012 (UTC)

Hi TR, Yes, but I meant: the actual values of the angles are unexplainable in the standard model.They could be anything.linas (talk) 15:00, 19 August 2012 (UTC)

I just struck everything out above, since its somewhat misleading, I fear. Its almost right, but might give you the wrong idea or confuse you. I am not sure I can give a short, intuitive, pop-sci and yet still technically correct explanation at this point. One really is a global SU(6) flavor symmetry, the other is a local su(2) gauge symmetry of pairs of particles picked out from the su(6) rep, twisted off at a wacky, unexplainable angle. They use the same symbol I for both, since its essentially the same thing, but .. Argghhh. One really has to look at what is happening to those doublets in the Lagrangian, and look at how the mixing is happening. It really doesn't help that I only studied this a very very very long time ago, at the dawn of time, and have forgotten important details. linas (talk) 04:28, 19 August 2012 (UTC)

I think it's probably impossible to give a clear explanation without going through the history. There was an original, empirical isospin SU(2) in nuclear physics, which made sense in the quark model as a symmetry between u and d (including left- and right-handed quarks). This got generalized in two different ways: first by adding flavors, to give SU(3) and eventually six flavors; and second by promoting the symmetry to a gauge SU(2) and including leptons, but no longer acting on right-handed quarks. The latter keeps the name "isospin." I think the meaning is somewhat split by field: to a nuclear physicist, the original strong-force isospin is the isospin, and to a particle physicist, the weak-force SU(2) is the real isospin (while the old strong-force version is a historical note). --Amble (talk) 06:26, 19 August 2012 (UTC)

Perhaps. But regardless of what one personally calls isospin, what I want to know is what is the I the PDG refers to in their reviews. Strong I? Or Weak I? Or is it context dependent? Because, as A. di M. pointed out, the "strong" isospin of an Omega baryon is 0, while it's "weak" isospin is not, and the PDG lists I = 0. But in the case of the photon, it's "strong" isospin is 0, but the PDG lists I = 0,1, which seems to be referring to "weak" isopin. Headbomb {talk / contribs / physics / books} 03:32, 20 August 2012 (UTC)

Aha. You want more accounting, and less philosophy! I believe what the PDG means by this is indeed the strong-force isospin. It's there for an eminently practical purpose: finding out which decay modes are allowed. And this notation tells you that the photon can participate in decays either with I=1, I₃=0, -or- with I=0. That's why, if you look at the decay modes for η'(958), you can find both ρ⁰ γ -and- ω γ. The original η'(958) has I=0, as does ω, but ρ⁰ has I=1. So the photon has to be able to enter the bookkeeping in two distinct ways. --Amble (talk) 04:19, 20 August 2012 (UTC)

OK, that makes sense now. (The way I thought about that until now is that electromagnetic interactions don't conserve nuclear isospin in the first place, so it's pointless to assign nuclear isospin to the photon, but now that I think about it, what the PDG do also make sense.) — A. di M.  10:20, 20 August 2012 (UTC)

Ah I see, I'm more focused on baryons right now [currently finishing a thesis on a new baryon nomenclature and a generalization of isospin to all quark pairs, not just u/d isospin], so I forgot about the stupid truly flavourless mesons. Not saying I understand what the PDG is hinting at, but at least I'll know where to focus my efforts to understand what they mean exactly. Headbomb {talk / contribs / physics / books} 14:25, 20 August 2012 (UTC)

Headbomb: Same thing for baryons. Look at the decays of Λ(1520). It has I=0 and can go to Σ π and Σ⁰ γ (where Σ has I=1), -or- decay to Λ γ (where Λ has I=0). It can't decay to Λ π because that would violate isospin conservation. --Amble (talk) 15:47, 20 August 2012 (UTC)

A. di M.: True: you could also say that EM interactions don't really conserve nuclear isospin in the first place. But they only violate it in certain ways. A photon never goes into the bookkeeping I=2, or I₃=±1, but only I₃=0, I=0,1. So this convention is more informative that just saying "does not conserve isospin" because there are decays you could write down that otherwise look OK but are actually impossible. --Amble (talk) 15:40, 20 August 2012 (UTC)

Hmm... I suppose I'll need to take a closer look at Λ(1520) → Σ + π and other such decays. Is that a strong or EM process? Because that seems to have ΔI = 2, which is both ruled out by my understand of the strong interaction, and which you also seem to rule out via EM processes in the above post. Headbomb {talk / contribs / physics / books} 16:49, 20 August 2012 (UTC)

Strong process. Keep in mind that you can't just add up all the values of I. The isospin acts like a spin, you have to add them in the sense of angular momentum coupling. Alse note the notation Λ(1520) → Σ + π really stands for three different final states: Σ⁰ π⁰, Σ⁺ π^-, and Σ^- π⁺. --Amble (talk) 19:33, 20 August 2012 (UTC)

Right, forgot that you need to add isospins like spins. Not quite sure that that implies, but I'll go over it tonight/tomorrow. Headbomb {talk / contribs / physics / books} 01:28, 21 August 2012 (UTC)

You really really really should read up on the representations of the rotation group SO(3). Sadly, WP is not the place to do it, we don't even have a stand-alone article on SU(2). But once you study angular momentum in depth, I think a lot of this will make a lot more sense. (Its the prototype for all the other SU's and opens the doors to many things) linas (talk) 05:53, 21 August 2012 (UTC)

The problem I have with group theory (and Lie algebra and related things in general) is that it's completely unpenetrable at the most basic of levels and I almost can't make any connections between the maths and the physics. I spent years trying to get a foot in the door, and while I can tell you that [for example] SO(3) is "the group of rotations in ordinary space", for me that's a sentence containing zero information, and I can't do anything useful with that. Luckily, you don't have to do things with group theory, you can do something equivalent with bra/ket formalism and big matrices, or alternatively, bra/ket formalism and the Pauli principle, and dodge group theory entirely. At least as far as SU(N) stuff is concerned. Headbomb {talk / contribs / physics / books} 14:30, 21 August 2012 (UTC)

I recently wrote a section about isospin symmetry: Particle physics and representation theory#Example: isospin symmetry. (I was using it as a simple example of how approximate symmetries give rise to groupings of particles.) I was assuming that isospin related only to up and down quarks, but it sounds like the truth is more complicated. Or maybe that I should clarify the way in which "isospin" is used. I hope someone can take a look and correct any inaccuracies... --Steve (talk) 12:42, 22 August 2012 (UTC)

As Amble explained above, this problem is terminological. Certainly, the strong isospin is a well-defined quasi-symmetry on ⓤ–ⓓ quark flavors. The trouble is about the meaning of the word "isospin" in general, because there are other 2-states (qubit) degrees of freedom to which the analogy to the spin-½ is exploited by certain high-energy physicists. Under just the same name, isospin. There is nothing in these analogies but the fact that all qubits are mathematically identical. This consideration is not a recent invention – it was known, for example, to Richard Feynman, well before all these 21-century quantum computings. A recent trend is to write the word isospin without a required precision, though. Incnis Mrsi (talk) 15:09, 22 August 2012 (UTC)

Stanislaw Ulam

Stanislaw Ulam has been proposed to be renamed, see Talk:Stanislaw Ulam -- 76.65.128.252 (talk) 04:40, 23 August 2012 (UTC)

Article Feedback

BTW, I noticed recently that you could access article feedback from your watchlist. It's a good way to make a link between the readers of an article, and editors, in that readers will often make suggestions for the article. Unfortunately, most of the feedback is useless, but there are a couple of gems here and there. It would be good for the physics project if people checked their watchlist's feedback every couple of days, and resolve issues as they arise. I'm sure it would greatly improve the quality of a couple of our pages. Headbomb {talk / contribs / physics / books} 17:21, 24 August 2012 (UTC)

I saw that too and have been looking through it occasionally. It's a pity they haven't done a full roll out. IRWolfie- (talk) 22:46, 24 August 2012 (UTC)

I don't think it is realistic to expect issues to be resolved as they arise, any more than we can expect all issues on the talk page to be resolved quickly. It might increase the usefulness of the feedback if some editors copy the good ones to the talk page or a todo list. RockMagnetist (talk) 01:43, 25 August 2012 (UTC)

Stephen Hawking at FAC

The article Stephen Hawking (one of our top importance articles) has been nominated as a WP:Feature article. If you have time, please have a look and leave comments at Wikipedia:Featured_article_candidates/Stephen_Hawking/archive3.TR 12:55, 26 August 2012 (UTC)

New editor contributing to and creating physics-related article

Please, could anyone take a look at Special:Contributions/Al126_at_wiki and maybe help the new editor? Some of their contributions have been deleted, and I'm not sure with the rest. Thanks for any assistance. --Vejvančický (talk | contribs) 12:11, 30 August 2012 (UTC)