Talk:Speed of light/Archive 2

message: This is a little strange, and I want to know if I am wrong, but it seems to me that no part of relativity theory would be inconsistent with the hypothesis that uncharged nuclear matter (like that comprising neutron stars) could be accelerated to arbitrarily high relative velocities, as by the intense gravitational field of another neutron star or a black hole.
The requirement for relativity theory is that all physical processes must take place with the same value for c. But if the physical processes involved have no electromagnetic interaction with the rest of the universe (as would be the case for neutrons), then there would be no theoretical prohibition against it having a relative velocity greater than c. If this is true (and not the result of a misunderstanding of relativity or some other theory), then I think it would provide better models for the merging of black holes.
I imagine evidence for or against this would be hard to come by. Since particle accelerators only act on charged particles, even if a neutron could be generated, greater-than-light speeds could probably not be achieved due to technical limitations. The only force that could hypothetically accelerate neutrons to velocities beyond c would be intense gravity. Detection of something like a neutron star travelling faster than c would have to take into account gravitational effects on nearby ordinary matter, much the same way that black holes are observed.
Can someone say definitively whether or not this hypothesis is consistent with relativity theory?
Reykjavikingur 01:30, 15 January 2006 (UTC)
replies: text: My understanding of relativity is that all matter which has a mass (charged or otherwise) increases in mass as its velocity increases. As the velocity tends to the speed of light, the mass tends to infinity - in other words, it would take an infinite amount of energy to accelerate an object to the speed of light. This does not affect photons since they have zero mass to start with. Birkett 17:59, 28 February 2006 (UTC)
thread_title:  Can uncharged nuclear matter be accelerated beyond c? 

message: This question has been raised before, but I still feel that it must be raised again. The writer states with assurance that recent experiments have shown group velocities to exceed c. I beg to differ. These experiments are some of the most debated ever in the history of science and many would go as far to question the moral velues and/or sanity of those advocating speeds greater than c. For example, recently the book "Faster Than The Speed Of Light" brought to light the ridicule faced by the author for propounding his theory. Nature even refused to publish his article for proposing something that challenges the foundations of one of the centurys two greatest theories advanced by a man who is often considered the impersonification of mordern physics, not to mention a Nobel laureate. Whether chnges do occur faster than the speed of light in vaccuam is a highly controversial issue and the author has no right to make the unaware reader believe that his next door neighbour regularly exceeds c. I request permission to make some minor changes to the section so the dispute among the scientific community is more clearly reflected.
Recently, some very strong evidence have emerged supporting the almost supernatural byproduct of Quantum Mechanics known as the Doppleganger Effect, the insteanteneous reflection of changes in one particle in another which implies transfer of information(since the state of a particle is definitely information). A compromise used by the Relativists to counter this is that c can not be exceeded in the 4 ordinary dimensions. However information may travel at c through extra dimensions curled up too small to be noticed(10/11 dimensional supergravity) so that it appears to exceed c.
:I am not aware of much controversy surrounding the experiments showing that the group velocity may exceed c. The group velocity is not the velocity of a physical object, hence such experiments do not contradict the relativity theory. The theory mentioned in "Faster than the speed of light" is very different: it does contradict relativity theory and it is not accepted by most scientists. I do not understand which experiments you are referring to in your second paragraph, but I guess it has something to do with quantum entanglement.
:You do not need any permission to change the article, you can just go ahead and change it. However, be prepared that your changes may be undone; in fact, this is quite likely if you don't support it by references to the literature. -- Jitse Niesen 20:07, 25 Mar 2005 (UTC)
thread_title:  Faster than c : Improper handling 

message: The opening couple of lines of this page is definitely in need of checking:
"The speed of light in a vacuum is defined to be 4 metres per second (1,079,252,848.8 km/h, which is approximately 3.1 miles per second, or 9miles per hour)."
What??
I can run faster than 9 miles per hour!! If I were to get in my car, I could exceed the stated "speed of light" without breaking any traffic laws!!
Assuming the 1,079,252,848.8 Km/h is the figure to be trusted, light speed is therefore  299792.458 m/sec.  I'll leave it to the physicists to do the metric to old conversion.
MSkerrett 14:41, 14 October 2005 (UTC)
replies: text: That was just some vandalism by user:166.109.0.79 It has been fixed now. The figures as they stand now are 299,792,458 metres per second (1,079,252,848.8 km/h, which is approximately 186,282.4 miles per second, or 670,616,629.38 miles per hour) , certainly enough to break traffic laws. Majts 19:45, 14 October 2005 (UTC)
thread_title:  Anyone got a calculator ? 

message: Let's say you had an extremely long tube in which there is a vaccuum.  On one end was an incredibly massive object and on the other an object(let's say a steel ball) was dropped.  Let's say that the tube connected right to the pole so that there was no cork-screwing.  Now the massive objects mass is about 10 times that its gravity accelerates all objects toward it at the rate of 100m/s/s. At the end of one second it would be going 100 m/s, two it would be 200m/s.  At one point wouldn't the steel ball be exceeding the speed of light? K-unit 17:35, 16 October 2005 (UTC)
replies: text: It is first worth pointing out that Newton's laws of gravitation can't be used to calculate accelerations in this case -- Newtons laws are only an approximation which works at the low-speed and low-mass limit. Secondly, it is true that an object can be massive enough to accelerate spacetime (and its contents) to the speed of light -- it is called a black hole. The mass has to be compressed into a tiny volume in order for sufficient acceleration to be achieved. Hope that's helpful. Rnt20 18:09, 16 October 2005 (UTC)
replies: text: Accelerate spacetime?  That's weird. --MarSch 15:19, 6 November 2005 (UTC)
thread_title:  breaking the speed of light 

message: The article Speed of light doesn't have the speed of light in common materials!!! as far as i know the speed of light in water is 2.5 x 108 m/s and in glass is 2 x 108 m/s. 59.93.129.144 14:45, 5 November 2005 (UTC)
replies: text: See the section "Interaction with transparent materials" where those values are given as fractions of the speed in vacuum. Tweak it if you like, realizing that someone might just revert it or change your additions, too (more likely to happen if you edit anonymously; it's quite easy to get a user name and long on first).  Be bold! Gene Nygaard 15:05, 5 November 2005 (UTC)
thread_title:  speed of light in common materials 

message: Question moved to reference desk Zhatt 22:40, 20 December 2005 (UTC)
thread_title:  Speed of light in a vacuum 

message: "The above equation was derived by Albert Einstein from his theory of special relativity, which takes the principle of relativity as a main premise. This principle (originally proposed by Galileo Galilei) requires physical laws to act in the same way in all reference frames."
In the quoted text above, shouldn't "all reference frames" be "all inertial frames of references"?
:yes, special relativity deals with inertial reference frames, but general relativity extends this to all reference frames. -MarSch 11:59, 16 March 2006 (UTC)
thread_title:  "Frame of reference" vs "inertial frame of reference"? 

message: The article sez:
For example, given that the equatorial circumference of the Earth is 40,075 km and c, the theoretical shortest amount of time for a piece of information to travel half the globe is 0.067 second.
True? Let's do the math!
Assuming this article is correct about the equatorial circumference of the Earth (it's close enough), 12,756 km would be the average equatorial diameter of Earth. For information to travel "half the globe" it need only pass through the center of the Earth, not travel along an arc on the surface of the planet.
Of course photons don't propagate through opaque solids (phonons do, at the speed of sound within that solid), and sound is slower than light, but there's no physical reason the information couldn't be transmitted with very very low-mass leptons, like neutrinos, which would pass right through the planet (and often do!) at very near the speed of light. So near the speed of light that, given the significant digits we have to work with here (five), the solution is the same. That's good, as it greatly simplifies the rest of the math, and I can just pretend that a signal the speed of light is passing through the Earth!
So, the speed of light is exactly 299,792.458 km/s, and it needs to go 12,756 km. Look mom, I can do basic division, and the solution is 0.04255 seconds! 63.5% the time the article claims! This would also be the solution if you ran a near-zero-latency cable straight down through the Earth to the other side (also not impossible, in principle).
The above solution defines the longest time (using average planetary dimensions) physically necessary to wait anywhere on (or in) Earth. So if by "half the globe" it means a hemisphere, and not the exact opposite side (which would actually end up being "all the globe"), the time is even shorter (70.717%. not 50%, as you F students might now be thinking).
Any signal that has a destination within the same hemisphere need not take as long as above, from the standpoint of physical possibility. For one entire hemisphere of the Earth to receive the same piece of information (transmitted omnidirectionally), the theoretical shortest amount of time would be 0.03009 seconds (this required using the Pythagorean theorem! oh no's!). This is 44.9% Wikipedia's claim (less than half! zomgwtfbbq!). And only the receivers on the very boundary of the hemisphere defined with the transmitter at its center would have to wait that long.
No matter how you interpret it, Wikipedia is wrong. Again. The statement in the article can only be valid if an artificial geometrical constraint is introduced, perhaps "the information must remain parallel to the surface of the Earth". It does not describe any theoretical physical limitation, as it claims to. Introducing an artificial constraint makes it meaningless within the context in which it occurs. 0.067 seconds is not a magic number on Earth. It only arises if you include unwarranted (not justifiable purely through physics) assumptions.
-08:12, 3 February 2006 (UTC)
replies: text: Information generally travels through optical fibers along the floor of the ocean, it doesn't simply pass through earth. Though this may be possible in theory, it's better to use a practical example, so a circumferential measurement is most appropriate in this case. If the information is still wrong taking this into account it should of course be changed. Richard001 06:31, 2 August 2006 (UTC)
thread_title:  Communications section is still bad 

message: I changed references to group velocity exceeding c to phase velocity doing so. This is the standard convention. one may read the phase velocity article or see a proof here .
:There are certainly experiments in which group velocity exceeds c. Are you absolutely certain that the experiments you changed are phase and not group velocity? Please provide citation. -- Xerxes 13:34, 2 March 2006 (UTC)
replies: text: Here are links to the experiments the article was discussing    which are about the group velocity exceeding c.  Howewer, this link (with paper references) suggests that the phase velocity or the group velocity can exceed c . -- ALoan (Talk) 15:19, 2 March 2006 (UTC)
thread_title: phase/group velocity

message: It says in the article that the speed of light is constant, regardless of the velocity of the object it was emitted from.
So the light will be travelling at the speed of light from both a staionary car and a moving car. My question is, doest the speed of this light remain constant relative to the car it was emitted from, or relative to an unconnected observer?
:Both. The speed of light is constant for all observers. -- Xerxes 18:09, 25 March 2006 (UTC)
replies: text: Another way to look at it is this: The medium for light (EM waves, in general) is (empty) space itself. So the speed of light relative to space is 3 x 10^8 m/s (1). When we say an object moves at a certain speed, it is with respect to something, and the something is not space, but some object like a building, the earth, solar system, and so on. But all these objects are in space, meaning their relative velocity w.r.t. space itself is zero (2). Combining (1) & (2), it turns out that all objects (including observers) will measure the speed of light to be the same irrespective of their velocities relative to each other. Rohitbd 10:48, 10 April 2006 (UTC)
thread_title:  Relative to what? 

message: Just came moseying through was wondering if the page should have some kind of reference to http://www.newscientist.com/article.ns?id=dn6092 perhaps this research has been proven wrong since I saw it way back? Its just your page lists light speed as being constant and makes no reference to this paticular line of research. Its all a bit out of my league so Ill leave you all to 'fight' it out to determine if it should be in or not. Hope you find it intresting at any rate. -- Shimirel (Talk) 03:27, 27 March 2006 (UTC)
replies: text: Since the speed of light in sensible units is 1, it is impossible for it to vary over time. What this research actually tries to show is that the electromagnetic coupling constant varies over time. This assertion is not well-received by the physics community, though research into it continues. -- Xerxes 18:18, 27 March 2006 (UTC)
replies: text: Hi Xerxes thanks for your reply as I said the page was a bit beyond me and I read it a while back and wondered if you editors might find it worth mentioning on the article. If you don't mind, would you please explain what the "electromagnetic coupling" is? Is it electromagnetism inside a photon or something else to which you refer? Confused  -- Shimirel (Talk) 23:50, 28 March 2006 (UTC)
replies: text: See fine structure constant - it measures the strength of the interaction between electrons and photons. -- ALoan (Talk) 09:22, 29 March 2006 (UTC)
replies: text: Thanks ALoan very intresting although if I'm honest pretty deep stuff, going to have to read these articles a few times to see if I can figure it all out. Thanks again. -- Shimirel (Talk) 02:18, 1 April 2006 (UTC)
thread_title:  Speed of light not a constant? 

message: The laws of physics also appear to prevent information from being transferred through more clever ways and this has led to the formulation of rules such as the no-cloning theorem.
Shouldn't that be no-communication theorem? --Tgr 08:09, 20 May 2006 (UTC)
replies: text: Yes, that should certainly be mentioned. But No cloning theorem also has something to contribute, towards the bottom of the "Consequences" section, so I think both articles should be linked to. Melchoir 08:41, 20 May 2006 (UTC)
thread_title:  No cloning? 

message: Image:Speed of light (Michelson).SVG
Added this to the Fizeau-Foucault apparatus
--Arnero 20:56, 25 May 2006 (UTC)
thread_title:  Measuerment 

message: It seems clear from the various edits made to this section of the article that:
# The quality of these edits are substantially lower than that of the main article.
# The information contained therein is irrelevant to an understanding of the topic of the article.
# The information is highly speculative and poorly supported by evidence that anyone before modern times was not just making up random numbers.
# People are just cheerleading for their favorite cultures.
On these grounds, I suggest that the whole section (up to the point at which experiments were actually tried but failed to determine the speed of light) be deleted. Support? Other opinions? -- Xerxes 19:49, 30 May 2006 (UTC)
replies: text: I feel uncomfortable removing a section which has good information, but I agree that it attracts edits of a low quality. I'd prefer to keep the section and watch it carefully. I cut out some of the more questionable parts. -- Jitse Niesen (talk) 02:35, 31 May 2006 (UTC)
thread_title:  Pre-modern speed of light nonsense 

message: Ed cited this article, as saying c does not stand for Latin celeritas. But he may not have read past the first sentence.  The article continues, Weber apparently meant c to stand for "constant" in his force law, but there is evidence that physicists such as Lorentz and Einstein were accustomed to a common convention that c could be used as a variable for velocity.  This usage can be traced back to the classic Latin texts in which c stood for "celeritas" meaning "speed".  The uncommon English word "celerity" is still used when referring to the speed of wave propagation in fluids. Finally, Although the c symbol was adapted from Weber's constant, it was probably thought appropriate for it to represent the velocity of light later on because of this Latin interpretation.  So history provides an ambiguous answer to the question "Why is c the symbol for the speed of light?", and it is reasonable to think of c as standing for either "constant" or "celeritas". --Blainster 22:55, 8 June 2006 (UTC)
replies: text: I read far enough to know that celeritas wasn't the only meaning. I'm glad of a second pair of eyes: constant or celeritas seems about right. Thanks, Blainster. --Uncle Ed 23:46, 8 June 2006 (UTC)
thread_title: C for celeritas