Wikipedia:Reference desk/Archives/Science/2011 July 19

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July 19

Gravity on earth if the sun vanished?

Another "what if the sun disappeared" question: Obviously it's impossible for the Sun to disappear, but if it did, and the earth obviously gets flung out into space, what would happen to the stuff on the surface of the earth at that moment? I'm not looking for a precise answer, just 'nothing' or 'everything'? On one hand, our 30km/s speed around the sun would (fairly) instantaneously become perpendicular to its original direction, however the entire earth and everything on it would experience exactly the same change so, would we even feel anything? The more I think about it the more I can't decide if we'll get completely splatted and flung off or if nothing much would happen at all. My gut feeling is that it would be catastrophic, but I keep thinking that there's no other "external forces" so why wouldn't it all equal out? I suspect that the gravity of the earth it self is what might stuff things up but I'm struggling to even conceptualize it. Or does this question fall into the impossible for it to happen so impossible to work it out? Vespine (talk) 02:28, 19 July 2011 (UTC)

No, it's easy to work out. At this distance from the Sun, its gravity is only a perturbation. All that would happen gravity-wise is that we would lose solar tides, which are already small in comparison to lunar tides. Looie496 (talk) 02:33, 19 July 2011 (UTC)

(ec)The effect on any one body couldn't be any greater than the difference between the sun's current force due to gravity on that body and its sudden disappearance. The appropriate equation is found here: Newton's law of universal gravitation. The effect would simply be the sudden lack of influence which currently produces that proportion of the tides due to the sun. A large sum over the earth but a small local effect of a few meters flow over six hours locally. There would be weird tides. μηδείς (talk) 02:36, 19 July 2011 (UTC)

(Enter a non-physicist, bearing vague science...) Er, I don't think so. You seem to be assuming that 'centrifugal force' operates at 90 degrees to the direction of the orbit of the Sun, whereas ... it doesn't operate at all. As I (the non-physicist) understand it, a steady gravitational orbit entails (at least according to Newton) objects carrying on in the direction they were going, except that gravity deflects then their path. If the Earth is heading towards Betelgeuse or wherever when the Sun spontaneously falls through a wormhole, it will carry on in that direction, oblivious. (apart, possibly for some minor tidal effects?) So yes, I doubt that we'll all fall through the ceiling, as we wonder why it's suddenly gone dark. AndyTheGrump (talk) 02:50, 19 July 2011 (UTC)

YES! I was totally thinking of cutting the string which is holding the ball swinging around your head, but you are right, that's completely incorrect! Thinking of the shuttle orbiting the earth, it's traveling fast enough so that its rate of "falling to earth" is matched by the rate of the earth's curvature falling "away" from the shuttle. If the earth wasn't there, the shuttle would continue to fly in a straight line and just stop "falling" to earth, it wouldn't just all of a sudden shoot away perpendicular to the earth... Nice one, that explains it perfectly.. Vespine (talk) 03:13, 19 July 2011 (UTC)

Do they give a Nobel Prize for vague physics that sort of makes sense? I want one ;-) AndyTheGrump (talk) 03:26, 19 July 2011 (UTC)

Here's one! Staticd (talk) 04:39, 19 July 2011 (UTC)

Err...try the Ig Nobel prize instead. ;) ~AH1 ^(discuss!) 20:58, 20 July 2011 (UTC)

No, cutting the string that holds the ball is perfectly analogous. It wouldn't knock the bacteria off the ball or tousle its fuzz. The relative scales are grander--and therefore the action "slower"--and the only catastrophe the ball faces is if it hits a wall or a person or some such, which inevitably it does on earth at our scale, bouncing all over, but would hardly happen to the suddenly unstrung earth-tennisball in the vast reaches of the floorless quasiobstaclelessness of space. No, Andy, no soup for you. μηδείς (talk) 03:35, 19 July 2011 (UTC)

Medeis is exactly right. The tennis ball does not "shoot away perpendicular", it does exactly what the space shuttle would do: just keep traveling at the same instantaneous tangential velocity as when the centripetal acceleration (tension from the string or gravity from the sun) disappears. Vague physics is my favorite, and in this case it is vaguely right :)

Though we really shouldn't say that "nothing" will happen either. When the acceleration due to gravity goes from some large number to zero instantaneously (let's say nearly so to avoid infinities), there will be a very large jerk (change in acceleration) for a short period of time. I have heard that jerk is actually the property of roller coasters that induces nausea, not the acceleration itself. So....SOMETHING will happen.RunningOnBrains^(talk) 05:02, 19 July 2011 (UTC)

(ec)This is right and wrong. The motion of the Earth if the sun vanished would be just like cutting the string of a ball whirling around your head. The idea that the ball suddenly makes a 90 degree turn is wrong. In both cases the Earth/ball just keep on moving in a straight line in the direction they were going when the string was cut/sun vanished.

On the other hand it's wrong that the fuzz on the ball is not tousled when the string is cut, and in this way the two situations diverge. If you were somehow standing on the ball while it was whirling you would feel a centrifugal force pulling you away from the direction of the string because the ball is being pulled by the string and you are not. If the string were cut, that apparent force would suddenly vanish and you would feel a large jerk. In the case of the Earth orbiting the sun there's no relative difference (or very little) between the acceleration of you and the Earth due to the sun's gravity. As a result you don't perceive any force associated with the Earth's orbit around the sun. If the sun vanished, the only observable change (besides it suddenly getting dark and a change in the motion of other celestial objects) would be the disappearance of tidal forces which are caused by the differences in force on various parts of the Earth (since some parts are farther from the sun than others). The jerk from the disappearance of tidal forces would be quite small, and if you happened to be somewhere where the sun was at the horizon you would feel nothing at all. Rckrone (talk) 05:16, 19 July 2011 (UTC)

Also important to remember is that the angular velocity of the earth around the sun is exceedingly slow, almost exactly one degree per day. Swing the ball-on-the-string at a rate of one-degree-per-day, at a constant rate. Oh, and the string would need to be about 25,000 times as long as the radius of your ball. So, imagine swinging a tennis ball on a 1/4 mile long string at a steady rate of 1 degree per day, and then cut the string. Tell me what the tennis ball does, and if you'd notice any major changes to the ball... --Jayron32 05:24, 19 July 2011 (UTC)

What if the sun disappeared because it got hit by a 10 solar mass neutron star traveling at 1 AU per month? Would that shake things up on Earth? 99.2.148.119 (talk) 05:31, 19 July 2011 (UTC)

Standing on the Earth, you wouldn't feel anything except changes in tidal forces. As long as the Earth is in free fall, there won't be any perceived forces on people standing on the Earth from the gravity of outside objects (besides tidal forces). Rckrone (talk) 05:40, 19 July 2011 (UTC)

ok, i think that all makes sense now. I don't know where I got the perpendicular thing from, what a noob mistake, it's been too long since I did physics :) Vespine (talk) 05:49, 19 July 2011 (UTC)

How much would the Moon's orbit relative to Earth change? Is the gravity of the Sun still practically constant even in all the space of the Earth-Moon system so there'd be no change? – b_jonas 08:18, 19 July 2011 (UTC)

It's not too hard to calculate this. The moon's orbital radius is about 0.0025 AU, so the difference between the sun's pull on the moon at it's closest point to the sun (or farthest point) and the sun's pull on the Earth is about 0.5%. The mass of the sun is about 333,000 Earth masses, so the sun's pull on the moon is right around twice the strength of the Earth's pull on the moon. So the tidal force on the moon at its strongest caused by the sun is about 1% of the force keeping the moon in orbit. That seems like it could be a detectable change, but still fairly small. Since the tidal force is always outward from the Earth, it seems like if it went away the moon's orbit would become slightly shorter, but I'm not totally sure about that. Rckrone (talk) 20:51, 19 July 2011 (UTC)

Enjoy this sight while it lasts and throw away this. We are ALL^{1 2 3} going on a long cold journey. Bring warm clothes and a torch. Cuddlyable3 (talk) 13:53, 19 July 2011 (UTC)

We may not have time for all that, because any collision that caused the sun to disappear may also throwout enough energy in our direction that causes us to go too, mere minutes later. Of course, in this universe, our mass-energy does not disappear and ends up being rearranged quite a bit. --Modocc (talk) 15:20, 19 July 2011 (UTC)

Wouldn't a ten solar mass neutron star be a black hole? If it weren't, its hitting the sun would still cause a Type 1a supernova, no? And how would such a large mass approach the sun without wildly throwing the Earth out of its orbit?μηδείς (talk) 22:08, 19 July 2011 (UTC)

I think i just worked out where I got the perpendicular thing from! I present exhibit A.. Konami, you have a LOT to answer for! lol Vespine (talk) 04:55, 20 July 2011 (UTC)

Suppose a solar-mass mini black hole plunged into the Sun from the opposite side of Earth so we didn't see it, and its centre migrated within the Sun, performing a mutual orbit with the Sun's centre until the Sun was eaten away. Potential climatic effects for sure. ~AH1 ^(discuss!) 20:58, 20 July 2011 (UTC)

Sanctum

In this movie they made multiple references to buddy breathing using a closed circuit rebreather. Given small gas canister for the rebreathers I do not think it is possible for any prolonged periods of time due to the significant gas escape. However in the movie they made this idea a part of the central plot. So how feasible is this procedure? (Igny (talk) 03:47, 19 July 2011 (UTC))

Here is a video of the procedure being practiced. You can try holding your breath in sync with a diver in the video. It seems feasible if one doesn't panic. Cuddlyable3 (talk) 13:39, 19 July 2011 (UTC)

The expression Three's a Crowd is apt here. Buddy breathing can be an opportunity to practice a Pranayama breathing cycle of 3 equally timed IN - HOLD - OUT periods. Cuddlyable3 (talk) 20:44, 19 July 2011 (UTC)

Dinosaur cloning

Is cloning of dinosaurs possible in near future? --Reference Desker (talk) 05:48, 19 July 2011 (UTC)

Making a few simple assumptions about your question, the answer is no. Dinosaur DNA would be needed to clone non-avian dinosaurs which became extinct about 65 million years ago. But DNA is fragile and it can only survive about a million years, even in the very best conditions, that includes in a mosquito stuck in amber. Now if you asked could we clone neanderthals? Maybe not 'soon', but that's not completely out of the question (leaving the ethical or practical questions aside). Vespine (talk) 06:07, 19 July 2011 (UTC)

Well, I was reading the article Timeline of the future in forecasts where I found A. C. Clarke had predicted dinosaur cloning will be possible in 2023. The reference for this claim, as given in the Wikipedia article, is Kurzweil Accelerating Intelligence. However after reviewing the other predictions by Clarke, most of which have failed, I not giving too much gravity to his prediction. But scientists in 2005 discovered soft tissue of T. Rex. So there is a possibility that dinosaur DNA can be found, is not it? --Reference Desker (talk) 06:21, 19 July 2011 (UTC)

There is a write up of what you are talking about here Tyrannosaurus#Soft_tissue. It sounds like this is still a controversial issue. I think that even if soft tissues or proteins are found, it does not guarantee that whole DNA has survived or can be recovered. Suppose we just have to wait and see how this plays out. Vespine (talk) 07:37, 19 July 2011 (UTC)

I read an article on this last year, but can't find the link now. It said that the T-Rex DNA they managed to recover was extremely incomplete, and pretty much useless. However, they have much better samples of Mamoth DNA, and it would be possible to combine this with an elephant's DNA and after a few successive generations of this, you would get a 98% Mamoth. No other Dinosaur DNA has survived that we know of. Zzubnik (talk) 08:18, 19 July 2011 (UTC)

I just want to make it abundantly clear that everybody here understands that Mammoths ARE NOT Dinosaurs. Dauto (talk) 15:34, 19 July 2011 (UTC)

"No other Dinosaur DNA has survived..." Really? Ghmyrtle (talk) 09:06, 19 July 2011 (UTC)

That's what the article suggested I should probably have said "usable", and it probably related only to fossil finds. As I said, I have no links for this, so it amounts to hearsay. Zzubnik (talk) 10:01, 19 July 2011 (UTC)

Ghmyrtl by link makes the point that birds are theropod dinosaurs. While that is the accepted evolutionary sequence it is not reflected in the normal separate understandings of "dinosaur" and "bird" in dictionaries. Wikipedia has an article List of animals that have been cloned. It does not include any kind of bird or dinosaur but another extinct subspecies was cloned briefly in 2009. Cloning even a single dinosaur seems far beyond our abilities. The OP is interested in multiple dinosaurs which could be sustained from re-extinction only by cloning at least a breeding pair. Apparently the Catholic church does not condone cloning. Presumably it is against the Will of the Judaeo/Christian/Islamic deity for creatures not selected by Noah to live. More on the religious theme, a Jehovah's Witness overseer recently informed a public meeting that God created dinosaurs for the purpose of pushing over trees to clear the ground for humans. That explains why God doesn't want them around any more. Cuddlyable3 (talk) 13:32, 19 July 2011 (UTC)

Do you have a reference for that quote? I think its brilliant--Jac16888 ^Talk 13:36, 19 July 2011 (UTC)

The JW quote? I was present at the meeting. Cuddlyable3 (talk) 13:42, 19 July 2011 (UTC)

Unless you have a quote from the Vatican that the Catholic Church considers dinosaurs people, I'm going to confidently say that the Vatican is not morally opposed to cloning dinosaurs, provided one has precautions in place to prevent them killing or injuring people. The Vatican doesn't have some 'no meddling with creation' position: it thinks messing around with human life, specifically, is wrong, especially experimenting on humans in a way that is likely to damage or kill them. It is also opposed to selecting human embryos for socially desirable qualities (as an offense to human dignity), and destroying human embryos, which I assume you would be too if you considered them humans. All of these would be involved in cloning humans. It really doesn't care if you experiment on dinosaur embryos. 86.164.72.255 (talk) 15:38, 21 July 2011 (UTC)

Why wouldn't be able to compute the most likely DNA sequence from first principles, synthesize that and use that to clone dinosaurs? Count Iblis (talk) 15:46, 19 July 2011 (UTC)

The Combinatorial explosion involved. The extent to which organ systems are interdependent on each other and environment suggests that it would be far easier to modify a bird species to look like the desired dino. Also, that would be indistinguishable from designing them. 99.2.148.119 (talk) 21:26, 19 July 2011 (UTC)

Also, it seems to me that recreating the giant insects of the Carbonifeous era should be a lot easier, as we have the DNA of modern insects to work with. Count Iblis (talk) 15:51, 19 July 2011 (UTC)

See the article Synthetic DNA. Manual design of oligonucleotides is a laborious procedure and does not guarantee the successful synthesis of the desired gene. The percentage of correct product decreases dramatically as more oligonucleotides are used. Cuddlyable3 (talk) 17:18, 19 July 2011 (UTC)

@Count Iblis: What "first principles" (not sure what those would be - please let me know if I misunderstand you)? If you are referring to coalescent reconstruction of the MRCA (reconstruction from today's DNA data from descendents), that is very imprecise, exponentially less so with increasing divergence time, and generally produces a probability distribution for each nucleotide (defying synthesis of one sequence). BTW, reconstruction would not depend on "first principles" - rather, it would be a backward extrapolation from current empirical data. -- Scray (talk) 17:54, 19 July 2011 (UTC)

What I mean is that if we knew everything about biochemistry, we could simulate hypothetical dinosaur like creatures using a computer. We could try out different genes to see if we get a good result and if we see something that looks good, we could create the animal in the lab. Count Iblis (talk) 17:54, 20 July 2011 (UTC)

I expect that in the future mankind might understand more about "genomic engineering." What in the genes or DNA would cause a living thing to have particular characteristics? If a rich guy in the distant future desires a pet which looks like a Velociraptor, what DNA sequence/what genes would be needed to be synthesized, or to be added to a related avian or lizard species, to cause such a creature to exist? In the 1700's, little was understood of chemical synthesis. By the early 20th century, chemists at IG Farben could synthesize a great variety of molecules with certain desired properties. 100 years from now, why wouldn't it be a straightforward process to start with a chicken (say) or a lizard, and diddle with the DNA until the resulting offspring looked remarkably like a dinosaur? Or to start with an elephant, modify the base pair, and create a creature hard to distinguish from a mammoth? Or go totally whacky, and add wings to a pony to create a (likely nonflying) Pegasus? Edison (talk) 04:59, 20 July 2011 (UTC)

Not sure about dinosaurs specifically, but mammoth cloning is currently more plausible and perhaps feasible. ~AH1 ^(discuss!) 20:52, 20 July 2011 (UTC)

Some weeks ago I listened to a talk by Svante Pääbo who managed to sequence the genome of the neanderthal. He also did some research on the kinetics of DNA degradation and came to the conclusion that it is impossible to isolate any significant amount of real dinosaur DNA. So the cloning of early humans, mammoths or saber-toothed cats could be possible in the future, but real dinosaurs are to old 192.124.26.250 (talk) 15:50, 22 July 2011 (UTC)

I saw a documentary on ABC Television (in Australia) recently about this. If I recall, the answer was "maybe". The documentary is available here, but only until 27 July 2011. Mitch Ames (talk) 06:48, 23 July 2011 (UTC)

autopilot

Hello can any one help me in navigation methods? what is the newest method in navigating whithout GPS now,can you explain aboat it? thanks — Preceding unsigned comment added by Ahsannet (talk • contribs) 06:44, 19 July 2011 (UTC)

Autopilot generally doesn't use GPS to navigate, it uses Inertial navigation system. INS is not a single "thing", but a collection of instruments and systems that can vary depending where and for what it is used. GPS can be used to feed the initial conditions into the INS and periodically to correct for errors, (there's even a separate article for GPS/INS) but it doesn't have to, INS can operate completely without a GPS. Vespine (talk) 07:48, 19 July 2011 (UTC)

The OP may be interested to read the article DARPA Grand Challenge and to follow links from there for more information on the topic. --Jayron32 12:42, 19 July 2011 (UTC)

ILS, VOR and DME (each has an article) navigation systems are not new but are in regular use by air traffic. GLONASS is the Russian alternative to the United States' Global Positioning System (GPS), the Chinese Compass navigation system, and the planned Galileo positioning system of the European Union (EU) and Indian Regional Navigational Satellite System of India.Cuddlyable3 (talk) 12:56, 19 July 2011 (UTC)

Note also that many of the systems cited above aren't navigation systems at all -- GPS (and related satellite constellation systems) are all positioning systems (thus the name). They tell you where you are right now. INS, despite the name, is the same thing. While accurate positioning is critical to navigation, a navigation process must also incorporate where you're going and how you're going to get there. The present modern schema for aviation navigation is RNP/RNAV. This is generally dependent on some satellite positioning system for accuracy, but can in many cases (when less accuracy is required, and where ground stations permit) be conducted with VOR and DME equipment as discussed above. Proper navigation then requires the use of particular algorithms to generate the correct heading from A to B, generally based on the WGS84 geodetic.

After all this, an autopilot (as opposed to the mere nav system outlined above) must deal with the dynamics and restrictions of the airplane -- how does it bank, turn, and climb, how does it burn fuel, what are dangerous performance envelopes -- as well as all the failsafe conditions that enter into play when you take control out of the pilot's hands. — Lomn 13:44, 19 July 2011 (UTC)

My pet mouse escaped and I found it again. What should I do?

Hello,

My pet mouse escaped to the street a couple of weeks ago and disappeared. Yesterday, I found him again, in quite a shabby state. I think he may have cohabited with wild mice during this period, so he might have caught some diseases. Is that possible? If so, what diseases? I live in Northern France. Thank you. 109.8.205.87 (talk) 07:05, 19 July 2011 (UTC)

Go to a veterinarian. --Reference Desker (talk) 08:04, 19 July 2011 (UTC)

Personally I'd put him in quarantine in a cage on his own for a couple of months, to see if anything develops. Zzubnik (talk) 09:59, 19 July 2011 (UTC)

It seems so amazing that a pet mouse survived in the wild for two weeks that I ask this silly question: Are you sure it's the same mouse? Cuddlyable3 (talk) 12:48, 19 July 2011 (UTC)

It does seem odd. I wonder where it was found. Was it definitely on the street for those two weeks, rather than down the back of some furniture? --Tango (talk) 20:08, 19 July 2011 (UTC)

I am sure it is possible for a pet mouse to survive in the wild for two weeks, if not traumatic as the questioner suggests. I also agree with Tango that the mouse most likely tried to remain near areas which smelled like the ones he had been associating with warmth, food, and shelter, so I doubt it strayed far. And of course if you really want a diagnosis, you need to ask a veteranary professional in your locale. Might I suggest asking Dr. Guénet of Département de Biologie du Développement, Institut Pasteur in Paris, the corresponding author whose email address is listed at PMID 16420748, for a referral to a competent mouse veternarian? 99.2.148.119 (talk) 21:37, 19 July 2011 (UTC)

I am happy that you found your pet again, and there are diseases that mice can spread, but fortunately most are rare. One mammalian parasite to be wary of is Giardia, but it is unlikely your mouse has caught that particular disease. Animals can be asymptomatic so I would avoid excessive handling for a week or two, and wash my hands afterwards. In any case, "don't panic", because your mouse may have simply had an urgent need to cohabit with these guys, and your veterinarian should be able to determine if there are any symptoms or signs of disease that should be treated. --Modocc (talk) 13:02, 19 July 2011 (UTC)

I am very touched by this story of this mouse. Sometimes the grandness of the world can impose anonymity that can be off-putting. I think I speak for my fellow Wikipedians that we wish your mouse all the rewards that life can offer a mouse. Bus stop (talk) 21:45, 19 July 2011 (UTC)

Tae yon kempy wee Moose. (video) Cuddlyable3 (talk) 14:55, 20 July 2011 (UTC)

I agree, it is nice when something like this happens. But just remember, when you sleep with someone, you're not only sleeping with them, but with everybody they've slept with too....

Two SI-units for amount of substance. WHY?

The SI article says: The seventh base unit, the mole, was added in 1971 by the 14th CGPM. But according to the ideal gas law, PV/T is already a measure of amount of substance. The corresponding SI-unit is Pa·m³/K, or joule per kelvin. The conversion factor is called the gas constant. One mole is simply equal to 8.314 joule per kelvin. The gas constant R pollutes equations of physics without any comprehensible justification. The mole is a pedagogical disaster. Can anyone tell me why it was standardized? Bo Jacoby (talk) 13:13, 19 July 2011 (UTC).

The ideal gas law applies only to gases, and not even real gases, just ideal gases. Moles are used in many other situations, such as chemical reactions in liquids. Jc3s5h (talk) 13:20, 19 July 2011 (UTC)

The mole has some historical reasons for its inclusion as an SI unit for number. While it is true to a point that there are other numbers which have limited applications, Avogadro's Number had become so entrenched in the literature, and as a standard (for example, the entire system of atomic masses depends on it) that it would have been pointless to take some obscure unit, like Joule per Kelvin (as used in the Boltzmann constant) or other non-intuitive derivation and make that the standard. For an analogous example from the ideal gas law: The universal gas constant often makes use of a really weird energy unit: the "atmosphere-liter". Dimensional analysis will prove that this is a unit of energy, but it is not nearly as universally useful or used as the joule or the calorie. Its the same deal with the J/K or whatever other random unit for "number" you can invent via dimensional analysis. The mole is both useful and used, so it is standard. --Jayron32 15:27, 19 July 2011 (UTC)

I can't really see joule per kelvin as a way to measure quantity. Though it's true you can use it if the ideal gas law applies, it often doesn't apply, and how can you talk about joules per kelvin as a unit of measurement for something that doesn't have that many joules per that many kelvins? It would just seem mad. Nay, the proportionality of the two numbers is a limited coincidence, like any of a vast number of proportionality laws that holds under limited conditions. Wnt (talk) 16:14, 19 July 2011 (UTC)

Yes , you are right. The mole is a completely unnecessary unit, but so is the meter (or any other SI unit for that matter). You could for instance use the light-nanosecond as a unit of distance instead (about a foot long). Tradition dictates that once adopted, units should be kept as long as there aren't any real reasons to drop them. Dauto (talk) 15:46, 19 July 2011 (UTC)

Peripheral to the main topic, but thank you, Dauto, for pointing out the light-nanosecond's near equivalence to the foot. I'm so going to use that! {The poster formerly known as 87.81.230.195} 90.201.110.222 (talk) 19:14, 19 July 2011 (UTC)

One can do away with all units. Units were only essential when we didn't have access to all of the relevant physics that relates all the units to each other. Then, because from a expermental point of view certain theoretical relations cannot be used in a practical way, we still have to use "dimensionally incompatible" units for measurement. But from a theoretical point of view, we can already do physics in a complete dimensionless way. Count Iblis (talk) 15:58, 19 July 2011 (UTC)

I can't see that. To me, units seem very important for knowing/keeping track of what it is I've calculated. I'm not even sure that's just a matter of error correction and not something more fundamental. Wnt (talk) 16:11, 19 July 2011 (UTC)

• There are very good reasons for different units. Humans are better able to extract meaning from numbers when the amount of digits used to represent a value are kept relatively low, say 0.001-1000. Numerals outside of that range don't have any intuitive meaning to people. This idea is closely related to (not idenitcal to, but in the same sort of concept as) The Magical Number Seven, Plus or Minus Two, that is there is a limited amount of information the human mind can attach meaning to.
• Think about phone numbers: They are always written with the numerals in groups of 3-4, like in the U.S. where you get numbers reported as (212)487-8891. There is a very good reason for that, the human brain is more capable of dealing with numbers with 4 or less digits grouped together, the same phone number is much less memorable as 2124878891.
• So measurement is designed with two things in mind: 1) Units which represent something I have experience with and 2) Units which keep the number of digits at a reasonable level. So, while I may recognize that a centimeter is about as big as the tip of my pinky finger, and a kilometer is about as far as I can walk in 10 minutes, my brain has a hard time working out how far 125,461 centimeters is in terms of my own personal experiences, and 0.0000485 kilometers makes little sense either. But one and a quarter kilometers tells me "as far as I can walk in about 12 minutes" and 4.85 centimeters is about the width across my hand. So we need multiple measuring units, because of the way our brains work. Certain types of measuring systems (like Natural units and Planck units) are very useful in very limited sorts of applications, but there's no reason to introduce these to the general population as a measurement scheme for everyday life. --Jayron32 16:27, 19 July 2011 (UTC)

• Phone numbers in threes is mainly a US idea - maybe you struggle more past three... It's 5+6 in UK (or sometimes 5+5 just to confuse).  Ronhjones  ^(Talk) 19:16, 19 July 2011 (UTC)

• No, it is because I am stupid. --Jayron32 20:53, 19 July 2011 (UTC)

Does Joules per Kelvin depend on the mass-energy equivalence to be considered quantity? 99.2.148.119 (talk) 16:44, 19 July 2011 (UTC)

Joules per Kelvin would require that the assumptions of the Ideal Gas Law and the Kinetic Molecular Theory more broadly were actually true, rather than approximations. Thus, since the IGL assumes that molecules have no volume or shape, have only elastic collisions, are not attracted or repeled by each other, etc. that is why the PV/T = number works. --Jayron32 16:58, 19 July 2011 (UTC)

That's not true Jayron. we could use J/K to replace mols if we wanted. It would work just fine. The OP is correct. The only reason we don't do that is tradition, nothing else. Dauto (talk) 18:50, 19 July 2011 (UTC)

Thank you for all your replies!

• To Jc3s5h: The ideal gas law is only needed here to define the gas constant which converts between mol and J/K.
• To Jayron32: The definitions of the mol and the J/K do not rely on Avogadro's law. The J/K is already a SI unit according to the SI rules for derived units, so it is not 'an obscure unit'. The atmosphere-liter is not an SI unit because the atmosphere is not the SI unit for pressure. The pascal times cubic meter is the SI unit for pressure times volume. It is the joule.
  • Reply to this one point: I find it confusing when you agree with every single word of my post, but then take a tone where you contradict me. Can you explain why you chose to do this? --Jayron32 20:05, 19 July 2011 (UTC)
    • Sorry. I am pleased that we agree! Bo Jacoby (talk) 12:54, 20 July 2011 (UTC).
• To Wnt: Measure amount of substance in any way you like and convert it to J/K, just as you may measure a length in feet and inches and convert to meter afterwards.
• To Dauto: the light-nanosecond is not the SI unit of distance, because the speed of light is not the SI unit of speed. The idea behind the SI was not to follow tradition but to drop unnecessary units.

You are being inconsistent. You can, if you chose, use the ideal gas constant (R) to eliminate the need to define the mol by fixing the value of R (say R=1 as you did). You may just as well chose to use the speed of light (c) to eliminate the need to define the meter by fixing the value of c (say c = 1 000 000 000 as I did). The two things are entirely equivalent. Dauto (talk) 18:48, 19 July 2011 (UTC)

That can be done, but that is not what the 14th CGPM did. The had already the J·K⁻¹. The molecule is a natural unit of amount of substance, and the reciprocal boltzmann constant is the number of molecules in one J·K⁻¹. The mole and the gas constant can safely be deleted from the physics textbooks, along with the calorie and the mechanical equivalent of heat. Bo Jacoby (talk) 12:54, 20 July 2011 (UTC).

• To Count Iblis: You argue that the SI is obsolete and should be replaced by natural units. That is right, but besides my point.
• To 99.2.148.119: No, joule per kelvin does not depend on the mass-energy equivalence. It can be understood by eighteen century physics.

My question was: why did they make the mol an SI unit? The answer seems to be: because the the 14th Conférence générale des poids et mesures was not aware that the problem was already solved. Bo Jacoby (talk) 18:34, 19 July 2011 (UTC).

They were aware of it. What you are forgetting is that the units were not defined to make physics equations look cleaner by removing unnecessary constants that pollute the equations. The SI units were defined to make communication of precise measurements between different labs easier. Now, in a lab people actually use balances to measure the amount of substance and the easiest thing to do is to choose some unit that makes that procedure easier. the mol was chosen so that 1 mol of pure carbon 12 has exactly 12 grams. Dauto (talk) 19:04, 19 July 2011 (UTC)

Another thing you are forgetting is that if you chose to use the ideal gas constant as a conversion factor so you can replace mols with J/K than any uncertainties in the measurement of that constant are automatically transferred to uncertainties in the definition of the unit you are using. That's not a serious problem nowadays since the gas constant is known up to about 1 ppm but that was not the case when those unit were established. Dauto (talk) 19:08, 19 July 2011 (UTC)

Is there evidence that they were aware of it? The mass of 1 J·K^{−1 12}C is 1.443268 g. No problem. Was the gas constant imprecisely known in 1971? Bo Jacoby (talk) 21:09, 19 July 2011 (UTC).

Of course they were aware of it. Or do you think you are the first person that noticed that? By 1971 the gas constant was well known but the mol standard had already been used informally for a long time and was well established as practice. As I said, in a lab people simply measured the mass of the substance at hand using grams as units instead of using the ridiculous unit of 1.443268 grams. Dauto (talk) 21:19, 19 July 2011 (UTC)

I do not claim to be the first person to notice anything. But neither is it beyond doubt that the 14th CGPM were aware of what they did. I suspect that they made a mistake by standardizing the mole as an SI base unit when they already had the derived SI unit J·K⁻¹. Bo Jacoby (talk) 12:54, 20 July 2011 (UTC).

I think you need to very carefully consider measurement accuracy here. I'm not 100% sure about this (I have a theoretical background), but it seems to me that a macroscopic standard for amount of substance based on a mass standard would be problematic, because the mass standard is the least accurate of what we have. There are efforts to get rid of the mass standard (a platinum bar stored in Paris, I think) by linking it to the number of atoms in some crystal, or by using the watt balance and defining Planck's constant to have some precise numerical value. But as long as the Kg is inaccurate, you want to avoid using mass if you don't have to. Count Iblis (talk) 15:53, 20 July 2011 (UTC)

"1 mol of pure carbon 12 has exactly 12 grams" says Dauto above. So the mole relies on the kg anyways. Bo Jacoby (talk) 19:57, 20 July 2011 (UTC).

Yes, but the problem is not whether you can find how much a mole of carbon weights. The question is how many times is a mole of carbon heavier than, say, a mole of protons. here is the mass of the proton taken from the PDG page:

$m_{p}=1.672621637(83)\times 10^{-27}\,kg$

$m_{p}=1.00727646677(10)\,u$

Notice that the second value (based on the definition of the mol) is about 500 times more precise than the first (which avoids using that definition). Dauto (talk) 20:33, 20 July 2011 (UTC)

The atomic unit of mass, u, is not based on the definition of the mole, and it is not an SI unit. Bo Jacoby (talk) 21:21, 20 July 2011 (UTC).

Silly you. The atomic mass is the mass (measured in grams) of a mole of some substance. Dauto (talk) 21:25, 20 July 2011 (UTC)

In other words, 1u = 1 g/mol. Dauto (talk) 21:32, 20 July 2011 (UTC)

It goes the other way round. The atomic unit of mass is by definition "one twelfth of the rest mass of an unbound atom of carbon-12 in its nuclear and electronic ground state". The word "mole" does not occur in the definition. Bo Jacoby (talk) 21:42, 20 July 2011 (UTC).

No, but look at the definition of the mole. Dauto (talk) 21:57, 20 July 2011 (UTC)

Yes, the definition of the mole depend on the definition of the atomic unit of mass, the dalton. I don't need the mole and my question is: why was the mole standardized as a base unit of SI? Bo Jacoby (talk) 22:20, 20 July 2011 (UTC).

The mass of atoms can be determined with much higher precision if you use daltons instead of kilograms. If you want a system that takes advantage of that high precision, it must have some unit related to the dalton. The SI defined the mol for that purpose. That made the SI slightly redundant. That redundancy seems to concern you. But it is a small price to pay for the increased accuracy provided by the use of the dalton (through the mole) instead of the kilogram. Dauto (talk) 00:06, 21 July 2011 (UTC)

1. Do you know that precision was the purpose, or are you merely guessing? The dalton (unit) serves the purpose as a non-SI unit. The mole would serve its purpose as a non-SI unit too, for those who need 8 significant digits rather than 6.
2. On page 7 in http://physics.nist.gov/Pubs/SP330/sp330sl.pdf is written: "Thus the joule per kelvin (J/K) is the SI unit for the quantity heat capacity as well as for the quantity entropy". This indicates that the CGPM was not aware that, according to the ideal gas law, the joule per kelvin is also SI unit for amount of substance.
3. The price paid by having two SI units for amount of substance is not a small one. It is a pedagogical disaster. The mole and the gas constant has infected the units and formulas of thermodynamics and chemistry. Concentration is measured in 'mole per cubic meter' rather than in pascal per kelvin. Specific entropy is measured in 'joule per kelvin, per mole' rather than simply being dimensionless. Specific enthalpy of fusion is measured in 'joule per mole' rather than simply in kelvin. Specific heat capacity is measured in 'joule per kelvin, per mole' rather than simply being dimensionless.

Bo Jacoby (talk) 11:58, 21 July 2011 (UTC).

1. Precision IS the reason the SI exists to begin with.
2. Obviously they thought moles were a better choice for unit for amount of substance otherwise they wouldn't have introduced it to begin with.
3. That's just your opinion.

Don't take me wrong. I think the SI isn't a very good system of units. I'm just explaining to you the reasons behind the SI units. The point is that the SI committee didn't simply blunder into defining an unneeded unit. They had their reasons. Dauto (talk) 17:09, 21 July 2011 (UTC)

1. The reason why the SI exists to begin with is described in history of the metric system. It was not precision.
2. The CGPM was adviced concerning the need to define a unit of amount of substance. (See http://physics.nist.gov/Pubs/SP330/sp330sl.pdf page 33). There is no evidence that the CGPM was aware that there is no such need. It was bad advice.
3. Yes I do disagree with your opinion: that making the SI redundant is a small price to pay.

Bo Jacoby (talk) 00:30, 22 July 2011 (UTC).

Strictly speaking a J/K isn't a unit of amount of substance, for the same reason that meters aren't a unit of time. J/K is specifically a measure of (internal) energy per degree of temperature. From the the ideal gas law we know that for ideal gases there is a relationship between J/K and amount of substance, namely the gas constant. Of course, that relationship only holds for ideal gases. The amount of internal energy as a function of temperature will generally be a non-linear relationship for most other substances, e.g. solids and liquids. By analogy, we know that distance traversed is related to time elapsed by a velocity. In the special case of photons and other massless particles in vacuum, that velocity is the speed of light. However, most other substances have other velocities. You are essentially asking why the unit of substance wasn't defined in such a way that the ideal gas constant had a numerical value of 1 in SI units. One could just as easily ask why the unit of distance isn't defined such that the speed of light is numerically 1 in SI units, or why the unit of mass wasn't chosen such that Newton's constant, G, has a value of 1. The answer is almost always mostly historical. The units that came to be adopted by the SI system were almost always chosen to closely to match units already in use, and in most cases, those units already in use originated because they were convenient for the people who most needed them at some point in the past. In the case of the mole, for example, it was historically convenient that there was a close relationship between amount of substance and weight in grams. Dragons flight (talk) 01:14, 22 July 2011 (UTC)

I think Bo is completely mistaken in asserting that J/K can be taken as a unit of amount of substance, or that one can properly convert between this quantity and moles. You can only properly convert between quantities if there is an absolute, fundamental physical principle linking them. The ideal gas law is an approximation, not exactly obeyed by any real substance. One cannot use it to establish an equivalence between two units. --Srleffler (talk) 04:26, 22 July 2011 (UTC)

No, Srleffler, Bo is right. The gas constant is a universal constant even though the gas law is only approximate and we could chose to set it to R=1(no units). In fact, the gas constant is given by the product of the Avogadro constant times the Boltzmann constant. What Bo is advocating is that the IS could have abandoned Avogadro's constant and had it replace with a different value carefully chosen to set R=1. Dauto (talk) 12:35, 22 July 2011 (UTC)

It doesn't matter that you can define the gas constant in terms of avogadro's number and the Boltzmann constant, nor that you can redefine it to be unity. That is math, not physics. The connection between energy, temperature, and number of molecules you are relying on is an approximation that is not exactly obeyed by any real substance. Number of molecules is a fundamental physical quantity. The ratio of kinetic energy to temperature is not exactly proportional to number of molecules for real gases, nor will the coefficient of that proportionality be exactly the same for all molecules.--Srleffler (talk) 17:42, 22 July 2011 (UTC)

Obviously my explanation went over your head. No body here is talking about ideal gasses. we are talking about the gas constant which does exist even though ideal gases don't exist. Dauto (talk) 19:51, 22 July 2011 (UTC)

Thanks for your comments! I do accept that the mole was standardized as a base SI unit, but my question is why? The SI-unit J·K⁻¹ was already defined in 1971, and the gas constant, 8.3144621(75) J·K⁻¹ per mole, is known to six significant digits, even if the ideal gas law is not exactly obeyed by any real substance, and 8.314 is not impractically huge or tiny like the speed of light and the boltzmann constant and the planck constant, so I see no good reason to make the mole an SI base unit. It seems as if the CGPM was badly adviced. Bo Jacoby (talk) 10:24, 22 July 2011 (UTC).

Part of the discrepancy between the CGPM's way of thinking and yours is that they are focused on physical measurement, while you seem to be focused on mathematics. SI base units are chosen so that they can have an operational definition, i.e. the units are defined by a physical experiment that can be performed, which provides a reference measurement against which to compare. SI units are not chosen for mathematical convenience or reduction of equations to a simpler form. Definition in terms of physical measurement is an essential goal of standardizing units: by making the system of units dependent on physical measurements that can be replicated, it becomes possible to ensure that the definition of units in use in different labs is the same, even when the labs are on opposite sides of the planet. This is not a trivial matter. While everyday measurements rarely depend so precisely on the exact definitions of units, technical applications often do.--Srleffler (talk) 17:42, 22 July 2011 (UTC)

Theoretical applications of dark energy

I understand that we know very little about dark energy, but I was wondering if our current understanding of it could shed any light on these questions. Despite being well beyond our technological capabilities, is it theoretically possible to "tap" into dark energy, and convert it into usable energy? And if so, and we were using up enough of it, would this slow the expansion of the universe? --Goodbye Galaxy (talk) 14:11, 19 July 2011 (UTC)

Yes, in principle you can extract work from the expansion of the universe. You don't necessarily need dark energy for this. If however, the accelerated xpansion of the universe is driven by dark energy and the equation of state of this is such that we'll get a big rip then, very close to the big rip, it will be easy to generate energy from the expansion of the universe. Count Iblis (talk) 14:29, 19 July 2011 (UTC)

Is there any discernable difference between dark energy and gravitational pull from beyond the visible universe? 99.2.148.119 (talk) 15:26, 19 July 2011 (UTC)

Yes. Gravity pulls objects through space, while dark energy expands the space between distant objects. --Goodbye Galaxy (talk) 16:01, 19 July 2011 (UTC)

So what would the observed differences be between dark energy and gravitational attraction from beyond the observable universe? 99.2.148.119 (talk) 16:37, 19 July 2011 (UTC)

While it does not directly answer the question, the Great Attractor may provide for an interesting read. What actually happens "outside the observable universe" is somewhat out of testability. If we had the means to determine what was happening there, it would be observable, n'est ce pas? --Jayron32 16:41, 19 July 2011 (UTC)

Changes in gravity propagate at the speed of light, no faster. (I suppose gravity wave must cover it) So there is no gravity from outside the observable universe. Wnt (talk) 17:04, 19 July 2011 (UTC)

Assuming that there was nothing prior to the big bang, which is a point on which most big bang experts are careful to remain neutral, if I remember correctly. 99.2.148.119 (talk) 20:45, 19 July 2011 (UTC)

The pertinent article is actually gravitational wave, which is very different. Red Act (talk) 17:39, 19 July 2011 (UTC)

Back to my original question, would such use of dark energy slow the expansion of the entire universe, or just the expansion of the region from which you are drawing the dark energy? --Goodbye Galaxy (talk) 21:35, 19 July 2011 (UTC)

Just the region, because the objects you would be using to extract it would be limited to the region. It might take billions of years longer than you expect before you can sell it on the electric grids. 99.2.148.119 (talk) 00:49, 20 July 2011 (UTC)

Asteroids in synchronous orbit

I was amazed by the discovery of asteroid 2010 SO16 2011. What other asteroids or comets are in synchronous orbits with Earth? I've read that there are two kinds of synchronous orbits, called "horseshoe" (like SO16) and "tadpole" -- but what does a tadpole look like? The Moon's orbit? Something hanging around a Lagrange point? 99.2.148.119 (talk) 15:28, 19 July 2011 (UTC)

I think this is the same asteroid as 2010 SO16 from which I found an article titled Horseshoe orbit which has an explanation of tadpole orbits as well. --Jayron32 15:33, 19 July 2011 (UTC)

Thank you very much. I've corrected above. Am I the only one who thinks it is very unlikely that an object that size would be just now rounding a Lagrange point in a synchronous orbit that stable? 99.2.148.119 (talk) 16:14, 19 July 2011 (UTC)

Is there an Earth-synchronous astronomical objects catalog, perhaps excluding Earth's satellites and debris? 99.2.148.119 (talk) 16:22, 19 July 2011 (UTC)

There's 3753 Cruithne and some other bodies in Earth-resonant orbits. -- Finlay McWalter ☻ Talk 16:25, 19 July 2011 (UTC)

Such objects are interesting, and the long-term stability of their orbits is interesting, because per square meter I can scarcely think of a place more likely to turn up alien artifacts in the Solar System, should they exist at all. Even things like 2006 RH120 that might be artificial... well, are we sure we know who built them? But probably it's more likely to turn up something alien if a satellite could stay in that orbit for a billion years, accreting various stray nuts and bolts from the near-Earth neighborhood, than if it has only been there a million years or less. Wnt (talk) 16:30, 19 July 2011 (UTC)

My sentiments exactly. I would like to know which politicians support exploring them. 99.2.148.119 (talk) 16:38, 19 July 2011 (UTC)

Then, you may be interested in the NASA website for Policymakers, and the NASA Office of Legislative and Intergovernmental Affairs. NASA publicly posts Policy Documents, which are matters of public record; and you can see which Senators and Representatives voted for or against specific laws, proposals, and so on, at the webpages for the Senate and House of Representatives. If you're really interested in diving into the NASA bureaucracy, proposals for missions trickle from individual scientists up through committees to the NASA program office specific to a particular Mission Directorate or a Mission Support Office; if new budget is required, the legislation starts here, proceeds here, and finally ends up at the office of the President, who signs or vetoes based on the political need and under the advice of the NASA Administrator. As a cynical observer, I would comment that the decisions are made by NASA administrators long before the matter is brought to a vote over legislation; NASA administrators have a pretty good idea about what will or will not be approved, so they don't make callous or frivolous proposals about speculative missions.

The Exploration Systems Mission Directorate is probably the most relevant group for asteroid exploration. Its director "is responsible for managing the development of flight hardware systems for future human exploration beyond low Earth orbit, including the moon, near Earth asteroids, Mars and its moons and other destinations." Nimur (talk) 18:31, 19 July 2011 (UTC)

Thanks! Email sent. 99.2.148.119 (talk) 21:03, 19 July 2011 (UTC)

I wonder who his counterpart in robotics is. 99.2.148.119 (talk) 00:47, 20 July 2011 (UTC)

You may also be interested in Hill sphere. ~AH1 ^(discuss!) 20:40, 20 July 2011 (UTC)

Astronomy review papers

Hi Reference Desk, I'm a teacher half a decade or so out of finishing my own education and feeling like I'm losing touch with the latest discoveries in what I previously considered to be my specialist areas. So my plan is to catch up over the summer holiday. Are there some good recent review papers in astronomy that I could use as the basis for a relatively informal literature review to achieve this? (Or barring actual review papers, papers that would be particularly good for chasing down the references to find other things to chase down the references in, and so on and so on until I come back to where I left off in the mid-00s.) I'm particularly keen to get up to date on exoplanets (which is an area that definitely seems to have moved on a great deal) and cosmology, especially dark matter and dark energy. Thanks in advance. --86.143.48.208 (talk) 20:02, 19 July 2011 (UTC)

I'm not sure all the exoplanet news could fit in a review article at this point, but here's a book you might want to ask your library to order or get on interlibrary loan. I'm partial to [1] on dark matter, which did make it through peer review, and at least parts of it certainly qualify as a secondary source. I also recommend catching up on wind power and fuel synthesis. 99.2.148.119 (talk) 21:12, 19 July 2011 (UTC)

The New Scientist magazines are a good read. Plasmic Physics (talk) 22:19, 19 July 2011 (UTC)

Review articles on current topics regularly appear in Annual Reviews of Astronomy and Astrophysics. Unfortunately, the published versions are not freely accessible, but in many cases you may be able to find pre-publication versions on the arXiv. --Wrongfilter (talk) 08:17, 20 July 2011 (UTC)

For a cursory glance at websites dedicated to astronomy, featuring regular articles and occasional scientific journal research, you may be interested in Bookmarking the following sites: Space.com Astronomy Today Universe Today Mars Today Bad Astronomy Sky and Telescope ScienceDaily Astronomy News APOD Cometography - Current Astronomy Education Review etc.. ~AH1 ^(discuss!) 20:30, 20 July 2011 (UTC)

Relativity with "flaws"...?

I was reading some news over at physorg.com, and some advertising caught my eye. It seems to be a site that claims to have a better theory than special relativity, and presents several "flaws" of the theory. Now, while I may understand some of the general concepts and equations of STR, I don't believe that I am to judge whether the site is comprised of crackpottery at its purest, or be making a point, which led me to post this thread.

So, the site is www.relativitychallenge.com. Among its claims, I found that the most prominent one is "Einstein's failure of the spherical wave proof" (covered in this article http://www.relativitychallenge.com/papers/Bryant.SphericalWaveProof.NPA2010.pdf) I searched in google and wikipedia and found no mention whatsoever of what this guy speaks about, which leads me to think that it may indeed be a crackpot site, or some guy trolling, but I still wanted to make sure.

Thanks in advance.190.24.186.224 (talk) 22:37, 19 July 2011 (UTC)

A quick way to judge if this website is full of shit is to score it using this method. #18 is very applicable here, and does not bode well from the start. --Jayron32 22:49, 19 July 2011 (UTC)

Why do you feel a need to make sure? Looie496 (talk) 22:53, 19 July 2011 (UTC)

Well I started reading the guy's articles and saw that he was kind of making sense, which started to worry me. Of course, now that I read further, there's a lot of really stupid mistakes there. 190.24.186.224 (talk) 23:04, 19 July 2011 (UTC)

At a glance, I can say with some confidence that it is bogus. Its "proof" that relativity is flawed is misusing Euclidean geometry whereas proofs involving relativity necessitate the use of nonEuclidean geometries. --Modocc (talk) 23:12, 19 July 2011 (UTC)

I'm not trying to defend it, but... I believe that this guy is talking about Special relativity, in which, as far as I know, euclidean spaces are still valid...190.24.186.224 (talk) 23:18, 19 July 2011 (UTC)

The problem with the geometry of special relativity is that to get down to the nitty-gritty of the math, you need to use some non-Euclidean geometries. Minkowski space is the standard geometric millieu for working this stuff out in. If you try to work this out in good-old-3D-Euclidean space, you miss the whole "time" part of "spacetime", which is kinda-sorta the whole point of Relativity. I know less than nothing about the specifics here, but I am fairly confident in those people who are far smarter than me who assure me that this all means something rather important about Relativity. That the author of that website completely ignores this stuff shows me he's probably no smarter than me, which is a bad indication that he's full of shit. --Jayron32 23:27, 19 July 2011 (UTC)

Shush. People like you killed Copernicus. --Kurt Shaped Box (talk) 00:15, 20 July 2011 (UTC)

That's correct. With relativity, time and space are not treated as independent entities. Instead, the geometry of space literally gets wrapped up together with time, such that they effect one another and theorists can only talk about them as either timelike or spacelike entities as a part of spacetime, hence even without the advent of multidimensional strings, relativity itself assumes a notion of spacetime that differs substantially from the historical Euclidean model that we are more familiar with. Thus modern physics has been more or less a method of explaining new physics with the assumption of these novel geometries. --Modocc (talk) 00:40, 20 July 2011 (UTC)

Be careful. The geometries of spaces with varieties of Minkowski signatures have been studied in what I personally consider to be an absurd amount of peer reviewed literature. 99.2.148.119 (talk) 03:32, 20 July 2011 (UTC)

Maybe you should point this out to the guys at physorg.com. I'm sure they won't like bad science any more than we do.--Shantavira|^{feed me} 06:24, 20 July 2011 (UTC)

In the "Spherical Wave Proof" article, the author comes up with this "Condition 2" that all points on the sphere must have the same radius. But then "Condition 1" isn't really a condition - if R may be different for different points then you can take any set of points, as you can find an R for any point. Anyway, he tries to convince the reader that the entries for R' in his Table II ought to be 1. This is not the case, as they are taken at different t', when the wave has propagated different distances. In the "Counter Arguments" section you can see that he doesn't see the point of transforming the time coordinate... Icek (talk) 09:14, 20 July 2011 (UTC)

See also here:

"I have proven that special relativity/quantum mechanics/... is wrong." You mean you did an experiment whose results disagree with the predictions of that theory? I didn't think so. You mean you proved it is self-contradictory? Not possible: Mathematically it's an elementary system, whose consistency is easy to check. You might as well claim that you can prove 2+2=5. (If you think you can do that, I'm willing to give you $2+$2 change for a $5 bill.) If you think you have found an inconsistency, you have probably made an assumption that is not implied by the theory. The fact is that these theories are not only well confirmed by experiment, but practical use is made of them every single day.

Count Iblis (talk) 19:26, 20 July 2011 (UTC)