# Talk:Variable speed of light

WikiProject Physics / Relativity  (Rated Start-class, Mid-importance)

I removed

the gravitational constant would change: ${\displaystyle G=3*m*c^{2}}$ (excess radius, Feynman, vol 2, ch 42)

I do not have that reference, but there is the formula Excess Radius = GM/(3c^2), may be something in connection to that was meant?--Patrick 09:51, Dec 14, 2004 (UTC)

## Removals of 15 December 2004

I removed some parts of the article, which I am copying here to explain my reasoning.

"Quantum physics (e.g., Feynman diagram) allows c to vary to any value within the limits of the uncertainty principle."

This needs to be explained or, at the least, a reference should be given. What formulation of the uncertainty principle is involved and how does that prove that c might vary?

"${\displaystyle \alpha ={\frac {e^{2}}{\hbar c}}}$ in cgs units where e is the charge of a proton"

What do cgs units have to do with this formula?

Are you serious about that question?? cgs units have everything to do with the expression of ${\displaystyle \alpha \ }$ when expressed as
${\displaystyle \alpha ={\frac {e^{2}}{\hbar c}}}$
if you were in SI (or simply any general system of units that does not constrain ${\displaystyle 4\pi \epsilon _{0}=1\ }$, then the expression for the fine-structure constant is
${\displaystyle \alpha ={\frac {e^{2}}{\hbar c4\pi \epsilon _{0}}}}$
That's the real expression for alpha, in terms of other physical quantities. r b-j 02:20, 21 Dec 2004 (UTC)
I see what you mean. You are talking about cgs units with the statcoulomb. I did not make the connection of cgs with esu (electrostatic units); probably because I'm used to using either SI units or Planck units. -- Jitse Niesen 16:50, 21 Dec 2004 (UTC)
cool. but if you're SI, then ${\displaystyle \alpha ={\frac {e^{2}}{\hbar c}}}$ is not accurate. it's not even dimensionless in SI. r b-j 18:54, 21 Dec 2004 (UTC)
"Dr Vladimir Dzuba has claimed [1] that it's meaningless to say if the speed of light is changing because it has units (it has been said that to get to the root of the changing constants problem, one has to look at unitless physical quantities - see above). But the physical quantity that determines the speed of light might be viewable as a unitless factor by the following reasoning. In the special theory of relativity, a space-time distance d is measured by pythagorean theorem, ${\displaystyle d^{2}=x^{2}+y^{2}+z^{2}+(c*i*t)^{2}}$ where x, y, and z are the first 3 dimensions of space-time and ${\displaystyle c*i*t}$ is the fourth dimension where ${\displaystyle i={\sqrt {-1}}}$
It's not just Dzuba that claims it. He references the Duff, et al "Trialogue" article. We must ask "How would we ever measure it if c changed, keeping all other constants the same?" and I have yet to see a persuasive answer to that. If ${\displaystyle \alpha \ }$ changes, we would know it from measurement, but we could not ascribe the change to c, it could be due to the Elementary charge or Planck's constant. r b-j 02:20, 21 Dec 2004 (UTC)

Therefore a meter = ${\displaystyle c*i*seconds}$
${\displaystyle c*i}$ is the conversion factor from seconds to meters. Time as a physical quantity is different from distance only by i. c is the correction factor to the historical error of thinking time and distance are different physical quantities. Meters could be defined as ${\displaystyle seconds*i}$ so that time and distance have the same units. To say that the speed of light is changing would then be to say that the relationship between the i dimension of space-time is changing relative to the other 3 dimensions."

If this is the opinion of whoever wrote it, it should be removed under the Wikipedia:No original research policy, otherwise references should be provided. Myself, I am not sure of the relevance of whether c is unitless or not: even if c is just a conversion factor, Dzuba's argument hold (compare with the conversion factor between feet and meters).

From the POV of humans with rods and clocks (or whatever measuring devices), c is not unitless because it is not dimensionless. In terms of Planck units, c is just the dimensionless 1, but before the meter was redefined, we measured c against existing standards of length and time. r b-j 02:20, 21 Dec 2004 (UTC)
I agree with everything that r b-j says. -- Jitse Niesen 16:50, 21 Dec 2004 (UTC)
"Humans need ideas to be valid (and distributable) in space and time in order for those ideas to fulfill the human need to survive and reproduce in space and time. In order for physics to make predictions about observations made by other people, first and foremost physics must be valid across space and time. Any "constants" that were found to be changing in space or time were either quickly eliminated from use or restated in an equation that would be valid in a larger range of space and time. Why publish a theory that can't be used in a distant time and place? The generalizations in physics we developed here on Earth appear to be valid in other galaxies at distant times, but it may not be just a coincidence. Galileo had a constant to predict gravitational observations on the surface of Earth, but we don't consider it a natural fundamental constant anymore because Newton made discoveries that enabled us to use a new constant G and equations to calculate gravity at any distance from a mass (not just the surface). Einstein's revelations showed that Newton's theory was not perfect and provided a new theory that enabled us to predict Mercury's orbit, and thereby extending Galileo's original observations to an even greater range of observation. Relativity equations could be said to be using a new constant, ${\displaystyle G*2/c^{2}}$ (from Schwarzschild radius), in the same way Newton's equations used a new constant to modify Galileo's ${\displaystyle 9.8m/s^{s}}$ acceleration constant. As another example, some astronomers may have once thought the distance to stars was some fundamental constant of nature, but Hubble showed it changes with time. As a third example, c has already been found to be different in different situations and new equations and constants of quantum physics are used to modify the old c in some situations. None of these examples show a fundamental constant changing with time, but they do show the introduction, replacement, and modification-by-equation of previously-held constants because we insist that our fundamental constants be constant or we stop believing in their sanctity. In the same way, if c is found to be changing, then we will introduce a new constant, replace it, or modify it with a new equation, but we may never view c as changing with time just as we do not view Galileo's ${\displaystyle 9.8m/s^{s}}$ as changing.

[ some stuff deleted by Scott due to article reaching limits and me agreeing that it needed deletion]

To Scott Roberts: I am sorry that I removed so much of your article, but I really think that the parts that I deleted do not belong on Wikipedia. -- Jitse Niesen 12:54, 15 Dec 2004 (UTC)

I agree with your comments with one tangential exception. Galileo didn't know "9.80000" wasn't valid on the entire surface, but neither did Newton know that his constant fails for mercury. I'll try to find references for the unitless c.

Although I agree with the comments as stated above, I now see there were other changes that were not mentioned that deleted and modified my statements that said light could travel faster or slower within the bounds of quantum mechanics. The following is my reference and argument that my previous statements were more accurate than the changes and that the faster-than-light wikipedia entry is in error.

Photons are commonly drawn at angles other than 45 degrees in Feynman diagrams. But photons are moving at speed c only at 45 degrees in those diagrams. To quote Feynman "...there is also an amplitude for light to go faster (or slower) than the conventional speed of light. You Found out in the last lecture that light doesn't go only in straight lines; now, you find out that it doesn't go only at the speed of light! It may surprise you that there is an amplitude for a photon to go at speeds faster or slower than the conventional speed, c." -- Chapter 3, page 89 of Richard Feynman's book "QED". I believe this is the fundamental basis of all the experiments that make individual photons go faster or slower than c. The new light-slowing experiments are not merely the old observation that photons "slow down" through a non-vacuum medium. That old observation is just multiple photons being absorbed and emitted in the molecules of the medium. The new experiments involve single photons, so that the slowing and speeding up of photons is real. To see how the uncertainty principle is involved to allow light to travel any speed, plug E=hf into the uncertainty principle's (E1-E2)(T1-T2) > h/(4pi) to get h(f1-f2)(T1-T2) > h/4pi where (f1-f2) is the precision of the frequency of the photon being studied and (T1-T2) is time interval. But f in quantum mechanics calculations is an exact number used in the summation of amplitudes, so c has to vary in order to allow f to remain a constant: use wavelength=fc to substitute (f1-f2)=(c1/w-c2/w). Rearranging, we get (c1-c2) > w/(T1-T2)/4pi where w is the fixed wavelength (frequency) of the photon being studied. So by the uncertainty principle, c can take on any value in the range (c1-c2) when you're analyzing intervals of time so small that they are subject to the uncertainty principle. Outside of the uncertainty principle (larger ranges of time), the individual amplitudes of quantum mechanics add up to produce a constant c. - Scott

I now understand that you were saying that individual photons can move slightly faster or slower than c = 299... m/s. However, I still don't see why "this is the fundamental basis of all the experiments that make individual photons go faster or slower than c." For definiteness, which experiment are you talking about? I think there is no experiment showing photons going faster than c, only experiments where photons slow down because of interaction with other matter. Furthermore, I'm uncomfortable with your use of the uncertainty principle: you say first that the frequency is not determined precisely and then that it is an exact number, so that c must change. My conclusion is quite the opposite: if you can use (E1-E2)(T1-T2) > h/(4pi), which is not totally clear to me, it follows that both the frequency f and the wavelength w can vary, but c is still a constant, like h and pi. -- Jitse Niesen 16:50, 21 Dec 2004 (UTC)
Photons are NOT localizable. They don't even have a noncovariant Newton-Wigner localization. What feynman was refering to is really the propagator. But the propagator does NOT really describe a photon created at a given spacetime point and annihilated at another. That's just a misinterpretation of quantum field theory. Phys 12:13, 4 Jan 2005 (UTC)

all this dispute seems to have done some good. i think the article has notable neutrality now, continuous modifications like the simple non-obstructive refrazing I have contributed seem to do the trick. so long as all the views are represented without hurting the concepts too badly, we can all get along in the intellectual realms here. . .

Surprisingly informative article, i like the theory that time slows, alltho it doesn't really confirm to my current uhm.. kosmology. i wonder if t slows, would there be circumstances where it slows slower, possibly circumstances that delay other generations(like nucleair reactions or lightemission), if so would you find exagerated entropy behind such a 'screen' (possibly like a bottleneck in a tidal area). If we can find such exagerated overly dense cosmic events i would assume t indeed slows. The 'speed' with what it slows appears very minor still, a wild guess would be 2 seconds in a billion years, larger values would probably somehow show in the fossil or geological record. Anyhow a slowing time is only a result of the big bang theory, and in that sense probably is moot as a cosmic value, when we interprete everything we can observe as local, wich imho makes more sense. In that situation i would hope t speeds and slows.uh? it's usually f that varies then? ah yes u have that.80.57.67.243 (talk) 17:13, 27 November 2008 (UTC)

## candidate for deletion??

i won't do anything about it, but this is still in discussion in the research (or speculative) end of physics. i don't think there is enough consensus among physicists to make this topic "encyclopediac". personally i do not think that variation in any dimensionful physical "constant" is meaningful because we do not measure dimensionful quantities without measuring them against like-dimensioned quantities. we would not know the difference unless some dimensionless constant has changed. if alpha changes, fine, but to ascribe that to c changing is speculative. maybe it should be deleted. r b-j 19:12, 21 Dec 2004 (UTC)

okay, now i am restating my original suggestion here that this wiki article is too much in the speculative end (perhaps someone's original research?) to be considered suitable for wikipedia. if it isn't deleted, it should be edited to show that this is about a speculative concept that a lot of physicists will have disagreement with. this is the kinda stuff Duff was complaining about: a New York Times article saying that the speed of light is slowing down when what really is the case is that some interpretations of some evidence is that ${\displaystyle \alpha \ }$ has maybe increased slightlty over 2 billion years. r b-j 02:35, 27 Dec 2004 (UTC)

By the above reasoning all references to string theory should be deleted from the wikipedia. Duff seems to be in the minority of physicists or at least cosmologists who think it's theoretically impossible for c to change. Otherwise, respectable journals wouldn't be publishing so many peer-reviewed papers on variable c models. Duff has not done the research on fundamental units and constants as shown in the 1st paper in the external links (Sep 2004 paper). Duff's last paper on the subject (July 2004) included objections from 3 others that he had to respond before they published his work, indicating that his view is outside the norm. People have a big interest in if the speed of light is changing, so as long as there are no factual errors in the article, i think it should stay. I tried to counter every argument r-b-j made while he ignored my questions. I have references in the article to support what is said where i expected r-b-j to object, even resorting to quoting for protection. The orginal research aspects i had in the article have been gone for sometime. I should point out that if the latest research is correct, alpha itself would no longer be dimensionless but have units of 1/time. Would that make it no longer a fundamental constant worthy of study? - Scott

one should go further to mention that so long as it is clearly stated that this theory is still disputed or has not yet gained widespread acceptence, there is no harm in displaying information about it. true, it can be disputed quite thuroughly, but it certainly hasn't been (and for that matter probably can't be)actually proven wrong. Information should be avaliable to whoever wants it written by whoever writes it. . . so long as both parties are aware of the situation. from this standpoint, what I suggest is simply that it be noted when an artical covers a controversial or disputable topic, but definately should not become a candidate for deleation unless it is plain derranged, though this could become controversial further as some would claim that this theory is thuroughly derrainged. so. . . if you think so, make a note to let people know that it's not to be considered fact. . . but don'd deleat it for christ's sake!

i previously said that i wouldn't do anything about it, but i am now changing that position. after posting about this to sci.physics.research where not one response (there were much fewer responses than i would have liked) took the position that "Duff's wrong and a variance of the speed of light could actually be measured", after a few other email conversations with Duff and physicists that are regulars to s.p.r, after waiting for Scott to post the theory he espouses to s.p.r for it to be tested by some real physicists (which, unless he is "zawy", has not been done at all), i came to the conclusion that because this theory decidedly has dubious physical merit, wiki readers should be alerted to that. so i put the "POV" tab at the head of the article. r b-j 21:32, 3 Feb 2005 (UTC)
The only vsl theory which has some relevance (IMHO), is creationist CDK theory, see e.g. [2]. From a scientific POV this very, very crackpot-style. At first sight you want to doublecheck, that you're not on Landover Baptist Church, but it has measureable attention.
OTOH, remodeling this article to cover that theory seems rather drastic, too.
Pjacobi 22:27, 2005 Feb 3 (UTC)
thanx for your input. as far as i'm concerned, you're preaching to the choir, but we'll see who's listening in. r b-j 01:43, 5 Feb 2005 (UTC)
I don't agree with Pjacobi that the creationist theory is the "only vsl theory which has some relevance". There do seem more serious theories, for instance that of Joao Magueijo (Imperial College London) which got some interest in the non-scholarly press. While it is definitely not mainstream, it was not rejected out-of-hand in conversations of theoretical physicists that I overheard, as the creationist theory would presumably be. Furthermore, one can build valid theories around a varying c even if it cannot be measured. Therefore I think "variable speed of light" is a valid subject for Wikipedia. However, I don't like the current article at all, even to the point that I am wondering whether it may be preferable to have no article at all instead of the current one. -- Jitse Niesen 12:31, 7 Feb 2005 (UTC)
Thanks for the name dropping. Indeed this gets enough scholarly hits [3] to be relevant and the main article getting 151 citations should not be taken lightly, even if 90% may have been dismissals.
But still no idea, how to proceed with this article.
Pjacobi 12:56, 2005 Feb 7 (UTC)

WikiPedia has lots of articles on things that are currently happening, so wouldn't it make sense just to add some tag to the effect that research is ongoing and try to be as thurough as possible about it? (I don't know anything about it... heh, just thought I'd make the suggestion. ;).

it's been a while since i had been ranting about this, but while i will not do anything to delete the article (hell there are people who believe that the Worldwide Jewish Conspiracy crashed the planes into the World Trade Center, why not talk about that?) i still will not concede scientific legitimacy to the concept of varying c. we do not measure nor perceive dimensionful quantities (we always measure or perceive them relative to a like dimensioned standard of some sort) and saying that any one of these dimensionful physical constants have changed, in and of itself, is, as Duff says, "operationally meaningless". r b-j 04:31, 27 July 2005 (UTC)

Well , i apreciate the pov tag, ofcourse it is controversial, yet as even a photon is a mere mathematical construct described as a constant, why not treat it as one (experimentally), perhaps when you slow light you are just making some new and inefficient kind of lamp,always.(thats similar to, c can't change because you can't measure it.)80.57.67.243 (talk) 17:37, 27 November 2008 (UTC)

## A changing C is meaningful

Contrary to the last post, i think a change in the speed of light could be a real thing and it would not necessarily cancel itself out. The most recent article about the Oklo reactors indicates alpha is changing which could very well mean c is changing (if electron charge and h have not changed). If only c and alpha have changed, then it is just an accident of the limits of our equipment and efforts that an alpha change was detected before the possible c change. Dirac himself was immensely interested in possible changes in the unitful G and Feynman himself discussed the issue and said it was not resolved (as of 1961). It is possible to simultaneously change c, G, h, and coulombs so that the known and useful unitless constants (i.e., nature itself) do not change. This situation is described in detail in planck units#Planck units and the invariant scaling of nature. On the surface the planck article makes it appear a change in c by itself is meaningless, but the article requires that all the unitless constants remain the same. In rhetoric and logic, this is known as begging the question or a "circular argument". The argument for the proposition contains the proposition itself. The article "proves" that we would not notice a change in c, but the first sentence makes a requirement (that all dimensionless physical quantities remain the same) that by definition means we would not notice the change. A change in c (without making any other requirements of other constants) would possiblly change G, h, and many dimensionless physical quantities and we would definitely be interested in the change. Likewise, if any dimensionless physical quantity changes, we are likely to see changes in other dimensionless physical quantities and c, G, and/or h. Physical constants with dimensions seem to be "put down" by some authors as not having as much meaning as the dimensionless physical quantities. But all measured constants of nature have meaning and are not just circular logic or historical accidents. We could define dimensions of "alphas", "proton ratios", and others to come up with values for c, G, and h that are without units or dimensions (plank units are not dimensionless, they are still expressed in units of planck length, time, mass, etc). Only for man-made reasons did we come up with the ideas of length, time, mass, etc and gave them units before stumbling upon "alpha units" and "proton ratios". The idea of "length" is just as arbitrary as the idea of "alphas". Our definitions and constants are arbitrary, but they important and valid because they are consistent.b - Scott aka 24.214.99.108

i wish you would register a handle with wiki and sign your "posts" on these talk pages so i can have some idea that i am making the same response to the same (or different) persons. however, do as you want. in the meantime, i'll address you as "24.214.99.108". is that okay? i made a response to you at the Talk:Natural_units, and am repeating some of it here.
But since there is an official standard for which constants are dimensionless, a variation in c has to be renormalized. If there's discussion about renormalizing it that can be considered notable, it should be included. If there isn't, it's a sign that physicists don't take it seriously enough to bother. 198.228.228.145 (talk) 13:49, 14 May 2013 (UTC) Collin237
i would not call it a circular argument. in some way it is a tautology or vacuous truth. but being so does not make it false; quite the contrary. it is saying essentially that when physicists (as well as the rest of us) measure any physical quantity, they measure it against some other like dimensioned quantity. in that, they are measuring a dimensionless number similar to when we commonly measure a length by use of a ruler and counting tick marks on it. so the vacuous truth is if ${\displaystyle c\ }$ somehow changes but all dimensionless constants remain the same, and all we can ultimately measure are dimensionless values, then we can't tell if ${\displaystyle c\ }$ changed and that "change" is meaningless in our existence. a better way to put it is that if ${\displaystyle \alpha ={\frac {e^{2}}{\hbar c4\pi \epsilon _{0}}}\ }$ changes (which is something we can measure), we do not know if that change was due to a change in ${\displaystyle c\ }$.
BTW, i do not consider it to be particularly bad to make a point by use of tautology. in my opinion, the weak anthropic principle is a tautology. saying it tells us nothing new, really, but it does help me think about a persistant question often posed by the intelligent design folks.
i dunno if the "ideas of length, time, mass, etc." are merely man-made, but clearly the definitions of the meter, second, and kilogram are. before the meter was redefined to it's present form, we had a definition of meter and second that did not depend on the speed of light. we made many different measurements of it and got different answers, mostly due to experimental error. in the sixties, when people became more and more confident about their measurement the meter was redefined because a good atomic clock was easier to reproduce than platinum bars with precise scratch marks on them. but now think about this, with this redefinition, the meter is the distance light travels in 1/299792458th second. that defines the speed of light to be 299792458 m./s . if ${\displaystyle c\ }$ changes, it is still 299792458 m/s. you can think of it similarly if you measured everything in Planck units no matter what ${\displaystyle c\ }$ is, it is still 1 in Planck units (and same for ${\displaystyle G\ }$ and ${\displaystyle \hbar \ }$).
now, i don't know why an atom's size is approximately ${\displaystyle 10^{25}l_{P}\ }$, but it is, or why biological cells are about ${\displaystyle 10^{5}\ }$ bigger than an atom, but they are, or why we are about ${\displaystyle 10^{5}\ }$ bigger than the cells, but we are and if any of those dimensionless ratios changed, life would be different. but if none of those ratios changed, nor any other ratio of like dimensioned physical quantity, we would still be about as big as ${\displaystyle 10^{35}l_{P}\ }$, our clocks would tick about once every ${\displaystyle 10^{44}t_{P}\ }$, and, by definition, we would always perceive the speed of light to be ${\displaystyle c={\frac {1l_{P}}{1t_{P}}}\ }$ which is the same as how we do now, no matter how some "god-like" manipulator changes it.
now if some dimensionless value like ${\displaystyle \alpha \ }$ changed, that's different. we would perceive the difference. but to attribute that change to a change in ${\displaystyle c\ }$, that case is not defensible. you could argue that the change in ${\displaystyle \alpha \ }$ is due to a change in the speed of light, and i could argue it's a change in Planck's constant or the elementary charge and there is no way to support one over the other.
please take a look at the Duff et.al. paper mentioned in the Planck units page. Michael Duff is a heavyweight, too. if you were watching Nova tonight, you would have seen him interviewed by Brian Greene. r b-j 06:43, 22 Dec 2004 (UTC)

As can be seen by your link to tautology, circular reasoning is used to make a tautology. Your argument only shows that dimensionless physical constants are important and that they must change if nature is to change. If c changes as determined by the time it takes eclipses on Jupitor's satellite Io to appear here on Earth, then it is a real change in nature and some dimensionless physical constants will also change. When we are discussing a change in c, i do not see why we must insist dimensionless physical constants are not changing. When you discussed the possibility of a alpha changing, did you require c, G, h, and electric charge to remain constant? No, you didn't. If you did, wouldn't your same reasoning show that a change in alpha in the presence of non-changing c, h, and electric charge require other dimensionless physical constants to change to such an extent that we would not know the difference? Or maybe it would show the equation for apha is in error. Either way, it seems the argument can be used both ways.

Since meters are defined as the distance traveled in c*seconds, c is a dimensionless physical quantity. c is basically seconds divided by seconds. It is nature's conversion factor between space and time. If c were suddenly c/2, then the fabric of space-time changes. Our old meter sticks would no longer agree with our definition of a meter. We would get less energy out of nuclear reactions via E=mc^2 .... Less energy is what the Oklo reactors are showing when they show alpha appears to have increased.

Michael Duff is a string theorist and string theory has not yet made it into physics because it can not be tested. Paul Davies is no less of a figure and he's arguing for a changing c. the paper you wanted me to read appears to show the debate about the importance of constants such as c, G, and h continues. The paper argues that c, G, and h are merely conversion factors between length, time, mass, etc. but this is not the same as saying that if any of them changes then it's meaningless. If nature's relationship between length and mass or between time and length changes, then i think it's of great importance. - - Scott aka 24.214.99.108

Circular reasoning is not the same as tautology nor is "circular reasoning ... used to make a tautology". A point argued with circular reasoning may or may not be true and the circular argument will not shed any light on its truth or fallacy. A tautology is true by definition, but it doesn't really say much. But at least it's true, albeit a vacuous truth. It's like saying 5x + 4y = 22 and 10x + 8y = 8(11 - y) - 10x . It's true, but it doesn't tell you much about x and y (because the equations are not linearly independent). It's like saying 5 = 5 or x = x. The problem with taking issue with a tautology is that, if it really is a tautology, then to dispute it, you're wrong. It's a lot like a truism. I realize that the problem with using a tautology in argument is to make an implication that is says more than it does. I am aware of this fallacy and I believe that I am steering clear of it, perhaps there is our dispute, I dunno. Tautologies really are simple truths and that why it's beyond me why anyone would dare to try to refute one. Perhaps deny that it's a tautology or refute some broader extension of a tautology (maybe that's what you're doing, I dunno), but if the tautology is accepted as such, it's only a loser to deny its content. It's like denying that 5 = 5.
Now Scott, I'm aware of the Oklo thing, lot'sa online references about it. Would http://www.ldolphin.org/recentlight.html be a good one? Now, I ask you, did you really read the Duff paper? It's the last third of: http://xxx.lanl.gov/pdf/physics/0110060 . It seems to me that you are not addressing the main point that he (and I) are making, as if it isn't there. It's like you haven't read it or let it soak in, but I will not make that assumption. Now I will say this, saying "string theory has not yet made it into physics" is ludicrous. Let's let the physicists say what is (or is not) physics. String theory is new and there is debate as to whether or not it is falsifiable (and if it is ever shown to be not falsifiable, it certainly will and should move from physics to philosophy, in my opinion) but just because it hasn't been tested yet, doesn't leave it out of the discipline of physics. How many years elapsed between Einstein's presentation of special relativity and the first experiments (mu meson decay?) supporting it? Was SR non-physics in the meantime? I think most physicists considered it to be an elegant and plausible explanation of some curious observation (the negative result of the Michaelson-Morley experiment) that was not yet confirmed. How is that substantively different from the state of string theory today? I hope you haven't used any bias you may have had regarding string theory as a reason not to read the point Duff is making. I think he does a better job of it than me.
So, to avoid misunderstanding, I'm gonna try to pick this apart, so we know precisely where we don't agree. The word "meaningful" is used by me if is or could be perceptible. If something or some change is not perceptible, it is not meaningful in my semantic. The distance from Vermont (where I live) to the Himalayas is meaningfully large to me but might not be if I were as big as a planet or perhaps if I lived for 10,000 years. The mass of a mountain is meaningfully large to me but might not be if, again, I were as big as a planet. The speed of propagation (light, E&M, gravity, any other ostensibly "instantaneous" action) seems fast to me given the scale that I sense distance and time. How I sense meaning in distance and time and mass has to do with how the matter and tissues and organs of me are constructed. It has to do with the fact that there are maybe about 1014 cells in my body, that each cell is about 105 times bigger than the atoms that they are made of and that these atoms are about 1025 larger than the natural unit of length. It is a matter of science (that we don't completely understand yet) that our particular beings are about 1035 bigger than the natural unit of length and we perceive scale in that same order of magnitude. If some God changes any of those dimensionless ratios significantly, life would be meaningfully different. For whatever reason, atoms need to be 1025 bigger than the natural unit of length and cells and the molecules therein need a minimum number of atoms so that they can function the way they do, and beings like us need a minimum number of cells to do what we do. A protozoa will not perceive reality like we do and a protozoa cannot exist at the scale of an atom and an atom cannot exist at the scale of ${\displaystyle l_{P}={\sqrt {\frac {\hbar G}{c^{3}}}}}$. You can go through a similar song and dance regarding how we perceive time relative to ${\displaystyle t_{P}={\sqrt {\frac {\hbar G}{c^{5}}}}}$.
The same is true regarding instruments we make to extend our range and accuracy of measurement of length and time and mass. The ratio of the wavelength of cesium radiation in an atomic clock to ${\displaystyle l_{P}\ }$ is some dimensionless number. And the ratio of the period of one cycle of this radiation to ${\displaystyle t_{P}\ }$ is the same dimensionless number.
Now if somehow, conceptually, ${\displaystyle l_{P}\ }$ increased, if these dimensionless ratios remained the same, we and our meter sticks (and the wavelength of that cesium radiation) would get larger by the same factor. A similar argument could be made regarding ${\displaystyle t_{P}\ }$ and our measurement of time. The meter and the second remain the same dimensionless multiples of ${\displaystyle l_{P}\ }$ and ${\displaystyle t_{P}\ }$ or some dimensionless quantities have changed, which is not the premise. Light (or other EM or gravity) will always travel one ${\displaystyle l_{P}\ }$ during the time elapsed by one ${\displaystyle t_{P}\ }$ and it's simply a matter of applying (invariant) scaling to say that this light will continue to travel 299792458 meters in the time elapsed by one second. If not, then some dimensionless quantity, which we can measure has changed.
It's sorta like the natural units define the tick marks on a sorta membrane (not to be confused with branes in string theory) of which all of reality exists. Stretch it in the time dimension and all times, including ${\displaystyle t_{P}\ }$ change by the same factor but not relative to each other. Stretch it in the length dimension and all lengths, including ${\displaystyle l_{P}\ }$ change by the same factor but not relative to each other. Same for mass and ${\displaystyle m_{P}\ }$. If not and some dimensionless quantity has changed and that change is measureable, perceptible, and meaningful. The quantities ${\displaystyle G,\hbar ,c\ }$ are simply diagonal slopes on this membrane and a change in any of these, such as c, would simply be a stretch in one dimension over another. Still, nothing meaningfully changed unless there is a change in times relative to ${\displaystyle t_{P}\ }$ or lengths relative to ${\displaystyle l_{P}\ }$, etc. All ${\displaystyle G,\hbar ,c\ }$ tell us is where these tick marks are relative to the units we have created to measure ${\displaystyle G,\hbar ,c\ }$ with.
Now the result of Oklo is that ${\displaystyle \alpha ={\frac {e^{2}}{\hbar c4\pi \epsilon _{0}}}\ }$ may have changed in the last couple of billion years. That, if true, is a meaningful change. It could be interpreted as a measurement of the speed of light, where ${\displaystyle c\ }$ is measured against another like-dimensioned quantity: ${\displaystyle {\frac {e^{2}}{\hbar \epsilon _{0}}}\ }$. So the standard of measurement against which ${\displaystyle c\ }$ is measured is ${\displaystyle {\frac {e^{2}}{\hbar \epsilon _{0}}}\ }$ and ${\displaystyle c\ }$ apparently has changed relative to that standard according to Oklo. Why interpret that as ${\displaystyle c\ }$ changing? Why not something in the standard that ${\displaystyle c\ }$ is measured against? Since, in my world of natural units (I can choose my units to be whatever I want and I choose them to normalize ${\displaystyle G,\hbar ,c\ }$ and ${\displaystyle 4\pi \epsilon _{0}\ }$). Then that result of Oklo would be the result of the elementary charge, measured in natural units of charge, being different long ago than it is now. It's just as plausible (more so for my money) than a change in c which is just stretching that membrane. r b-j 06:17, 23 Dec 2004 (UTC)

We're going to have to agree to disagree. Yes, I did read all three papers, and came across plenty of statements that support my position. For example, Duff says "Indeed, papers on time-varying c are currently in vogue as an alternative to inflation. I believe that these ideas, while not necessarily wrong, are frequently presented in a misleading way and that the time-variation in the physical laws is best described in terms of time-varying dimensionless ratios, rather than dimensionful constants." My position is supported when he says "I believe", "not necessarily wrong", and "papers on time-varying c are currently in vogue". He also states some consider c to be unitless and that particle theorists do not even use length or time units but view everything in terms of mass. Duff is trying to get people to disregard dimensionful constants when working in string theory, but he also said c can be stated in terms without dimensions. He does not address what happens if c changes without a change in G.

Again you demonstrated that a "change in c" is meaningless if there is no dimensionless factor that has changed. I agree. You said allowing them to change is not part of my premise, but neither is forcing them to stay the same. In order for them to stay the same G, h, and/or e would have to change by some remarkable coincidence(s) to precise value(s) that allowed the dimensionaless physical constants to remain the same. In discussing a changing value of c, you have added the requirement that no dimensionless constants change. I do not need to go further to make my point, but i'll state that even what's considered a dimensionless constant is a man-made historical convention. Even Duff agrees that many now consider c dimensionless.

Then, looking at it the other way, you demonstrated that if a dimensionless constant changes, it is meaningful if constants with dimensions are allowed to change. Why is allowing dimensioned constants to change part of your premise? So again i ask, why isn't what's good for the goose, good for the gander? If you are allowed to change my dimensioned constants to prove your point, why can't I change your dimensionless constants? Try changing alpha without changing h, c, or e. Express alpha in planck units if you need to. You would have to conclude that the equation for alpha needs adjustment. Then i could do the same to keep alpha the same if c changes. Either way, the changes in nature are real. So now i see i can prove my case even under your requirements: if you want alpha to stay the same, then i can claim the equation changed which is why c was allowed to change by itself. Now supposed alpha and only alpha changed in the same way. Then it's the same darned thing! Divide c or multiply alpha by the same factor. To claim one perspective is better than the other is just semantics. To claim a change in c by any other method (allowing dimensioned or dimensionless constants to change) is also just as real as a change in alpha that allows dimensioned or dimensionless constants to change, provided you do not insist the formulas for planck units are a message from God, as explained below.

By insisting planck units will always = 1, you are forcing the G, h, and e to change in response to a change in c. This forces the dimensionless constants to remain the same which is why you are having a hard time abandoning your position: you think planck units=1 is a fact of nature. No, it's a human definition. In discussing a change in c, i do not think we should force G and h to change in order to keep plank units = 1. If c changes with time and G, h, and e do not change precisely as is required to allow plank units to remain = 1, then the formulas for the plank units have to be modified to include a new constant (as was done before since planck's paper was a modification to an 1870 paper to incorprate h) or to make them a function of time so that they can remain equal to one. This could be our point of reconcilliation. A change in c is a fundamental change to our concepts and therefore to the equations we have invented. You are insisting that God change c, G, h, and e at the same time and in a precise way in order to keep your man-made planck units = 1.

The above should show that "length" or "mass" is no more meaningful from God's point of view than "alpha units" or "proton ratios".

- Scott

be careful about what you ascribe to what i say (or "insist on"). i do not insist on God (if i am a theist) or Nature (if i am not) changing any of the dimensionful constants. i do say that, within small factors of ${\displaystyle 4\pi \ }$ that physicists might debate, that the Natural units as defined by Planck (with the extension of the so-called Planck charge) are absolutely not human constructs. ( i am of the school of thought that Planck should have normalized ${\displaystyle 4\pi G\ }$ instead of just ${\displaystyle G\ }$ and then we would have also defined the unit charge to normalize ${\displaystyle \epsilon _{0}\ }$ instead of ${\displaystyle 4\pi \epsilon _{0}\ }$, those would be more natural, but that is another debate and that does not change the scale appreciably nor changes the invariant scaling issue a tittle. ) those are the units inherent to nature and if you want to express any physical quantity unamibuously (so you can communicate that quantity to some alien that has no idea what a meter is nor gives a rat's ass about the density of water), without respect to any particular "thing" in the unive you must express it in terms of Planck units (or, again my preference) the "rationalized" Planck units with ${\displaystyle 4\pi G\ }$ and ${\displaystyle \epsilon _{0}\ }$ normalized.
there are numerous items Scott made that i could go down and dispute, but it's just too much work. i would rather stick to the main issue of how we would ever know if a dimensionful universal "constant" has changed without confusion about whether something in the like dimensioned standard that we measure this dimensionful universal "constant" against has been the quantity that has changed. r b-j 01:08, 24 Dec 2004 (UTC)
That's a lot of text you two have been generating. Let me try to summarize. Consider the following two events:
• α halves and c doubles; h stays constant.
• α halves and h doubles; c stays constant.
Am I correct in saying that R B-J thinks that no experiment is able to distinguish between these two events (this is his definition of not meaningful) while Scott thinks that it is possible to distinguish between these events? -- Jitse Niesen 22:16, 23 Dec 2004 (UTC)
if a single experiment (or multiple runs of the same experiment) says that ${\displaystyle \alpha \ }$ is now half of what is was yesterday, i am saying that that measurement is conceivable possible (but for all i know, the universe turns into a tomato if that happens, ${\displaystyle \alpha \ }$ halving is pretty damn radical) and, from that experiment alone, there is no meaning in saying that it is from ${\displaystyle c\ }$ changing vs. ${\displaystyle \hbar \ }$ or ${\displaystyle \epsilon _{0}\ }$ or ${\displaystyle e\ }$.
perhaps there are other dimensionless constants with ${\displaystyle c\ }$ in them that have changed in a manner that would be consistent with ${\displaystyle c\ }$ doubling. that would lend support to the speculation that ${\displaystyle \alpha \ }$ was halved because ${\displaystyle c\ }$ doubled. Oklo doesn't tell us that. Oklo only tells us (that maybe) alpha had changed by a small amount in 2 billion years. and that result is still debated, however i do not take that debate to mean that result is not accurate.
i have one last suggestion about this. i would suggest that instead of arguing about it here, we take it to the USENET group sci.physics.research and see what those guys say. i have had a few misconceptions corrected by them. it doesn't hurt. r b-j 01:08, 24 Dec 2004 (UTC)

## Continuing

I see we're over the 32 KB limit. I misread 22 as 20, and did an algebra error, so why not delete the algebra part and all the string theory stuff? Despite Niesen doing a fine job of trying to curtly resolve this, I unfortunately agree with everything rbj said in reply, except i would add that i only need to compare my old meter sticks with light and a clock and look at eclipses on Io to see how well the change could be contributed simply to a change in c...and that if i did the measurements carefully enough, i could have detected the change before others detected the alpha change. I see the simple question i asked twice apparently cannot be answered simply. rbj wrote: "i would rather stick to the main issue of how we would ever know if a dimensionful universal "constant" has changed without confusion about whether something in the like dimensioned standard that we measure this dimensionful universal "constant" against has been the quantity that has changed." my reply: we would need to check the constant in at least 2 different ways (Io, atomic clocks, and alpha) to resolve the confusion....there is still confusion in an alpha change because we do not know if h, c, and/or e has changed. We'll go to sci.physics.research. - Scott

and again, if the speed of light changed (and nothing else changed), then your "old" meters sticks and/or your clock would be updated in such a way that light would continue to travel 299792458 updated meters in the time elapsed by one updated second and you and i would be oblivious to the change. if you say, "no that is not true, see here it travels 299792457 meters per second." then i say that the dimensionless ratio of your meter length to the Planck length and/or the dimensionless ratio of your clock second to the Planck time, at least one of those dimensionless numbers has changed and that is the sailent, measurable difference. and i would also say that saying it is a tautology: it's pretty damn obvious and it really doesn't say much -- but it's a safe truth. i'm happy if you post this to s.p.r . recently someone else (i think it was someone else) posted a very similar question about whether c is unitless or not. i would say, it depends on how you define things. if your unit time is the second (defined the traditional way, with a cesium atomic clock) and your unit length is defined to be 1/299792458 second (with c as the reference), then c is the dimensionless number: 299792458. but then the problem with your position is that c cannot change. c is always 299792458. you cannot say that c is both dimensionless and that it is changing. well, you can say it, but that would be tangibly in error. and i think that the guys on s.p.r would back me up on that. r b-j

The current definition of a meter is based on the desire to be as close as possible to the old meter sticks. As i said before, if the speed of light changes, we have every reason to view that definition as no longer reasonable and go back to the old meter sticks. In your world, the new 8 mm nuts would only fit the old 4 mm bolts and yet you say we would be "oblivious to the change". Every manufacturer in the world would tell you to go to hades if you asked them to keep your definition of a meter. But your last point is something i can relate to. It assumes meters are just a human's way of looking at seconds that are not in the i dimension, as might be a proper view of relativity. In this case, c is just a conversion factor for human units and nothing to do with nature. It means our old meter sticks would never need correcting because the actual length of meter sticks change if c changes and they change in such a way that we do not notice it. A changing c would merely mean we've change the definition. So maybe a real changing c would have to mean relativity is in error. But how are we to know if this view of relativity is the correct one? How do we know that space is just a different way of measuring time and that therefore the relationship (ratio) between space and time (via relativity) cannot change? With a good quote from an authority, i could finally write an intro for the article that you would agree with: that a changing c is meaningless if we are to keep our view of relativity. But if i now agree with you on c, it does not mean i agree that dimensional constant changes are meaningless, and my prior questions still apply if you replace c with G or h. I am only admitting c is a particularly odd dimensionless constant that is meaningless because it is the human conversion between seconds and seconds. - scott

i think you need to test your ideas with a wider jury. some of what you just interpreted from what i said does not represent my position, but i am tired of repeating it. other of what you said sounds at least unconventional ( "So maybe a real changing c would have to mean relativity is in error. But how are we to know if this view of relativity is the correct one? "). i think that the Michaelson-Morley experiement spoke to that one. Please, Scott, let's not debate this here. let's take it to sci.physics.research . i think you should be the first to post about it because i cannot and will not try to represent your position. you need to initiate the debate. again, my position about this is that it is currently at the speculative end of physics, not orthodoxy at at. i thought that wiki or any encylcopedia is a source of info on mostly "mature" subjects that have settled a bit. not speculative, unsettled, and widely debatable topics. that's a wiki policy issue that should probably go to the talk pages of wiki policy pages. r b-j 17:13, 24 Dec 2004 (UTC)

I haven't had much luck getting good responses from s.p.r. Your description for a unitless constant c requires changing the definition of meters as c changes. If you stick with the old meter sticks as the definition, then the unitless c can change. I'll place more weight on meter sticks than on definitions. - scott

i dunno when i'm gonna tire of this. i still wish you would take this to a venue or persons much more expert in physics that i am (i am an electrical engineer, but i am still pretty confident of the physics that i have learned). however, Scott, i wonder if you realize the internal contraction in your assertion. to repeat, if on one hand, you define the unit length as 1/299792458 second, then c is the dimensionless number: 299792458 (or 299792458 sec/sec which is a ratio of like dimensioned quantities and therefore dimensionless). on the other hand, if you use the previous definition for your unit length as the distance between two scratch marks on a bar of platinum (a pretty stable meter stick), then your unit length is not the same dimension as time. it is length and defined completely independent of c or any notion of time. and then you can measure c independently and, each time you measure it, if you're really good at it you will get the result 299792458 m/s (not dimensionless), and because of experimental error, with a small +/- error that would likely be different for each experiment. perhaps, conceptually, there will be a trend that shows this value of c is slowly decreasing in time. i think that is the case you are making. but that is not a dimensionless value. you are measuring c against your pre-existing definition of a meter and second and all you know is that this ratio of c against a meter/second appears to change. there are two (actually three) possible ways for that to change. maybe your meter stick got a little longer. maybe your clock ticks a little faster. those could just as well be the source of your apparent downward trend in c.
but the thing is that none of the properties of your meter stick nor of your clock go into the fundamental equations describing physics. but c, h-bar, and G (and epsilon_0) do. and if all of reality is described or measured in terms of the Planck units, those constants go away (they become 1). but those equations are still there, doing their thing. then the physical reality that builds subatomic particles and atoms and molecules and crystal lattices and DNA and proteins and biological structures (cells) as well as stars and all things still happens. it's just that we are now looking at them in terms of the scaling standard of Planck units. but in this case, there is no c to change, no G to change, etc. c is just the unit speed and will always remain so. that is the salient concept of Natural units. in terms of these Natural units c cannot change any more than 1 can change.
so you say, "hey, we're not using Natural units, we're using meters". i say (again and again) your meter stick is a dimensionless quantity multiplied by the natural unit of length. if that dimensionless quantity changes, then something really change. maybe more atoms went into it to make your meter longer. maybe some were taken away. we would call that an experimental standard problem (which is why they redefined it in 1983 anyway). perhaps the number of atoms stayed constant (that's a good meter stick) but the size of atoms relative to the Planck length has changed. THAT DIMENSIONLESS QUANTITY IS THE SALIENT MEASURE. (or, perhaps the one that relates your clock tick to the Planck time.) to say that it is c that is changing here is, from the POV of an experimental physicist, mistaken. r b-j 03:20, 25 Dec 2004 (UTC)

I am also EE. Einstein was using scratch marks on a bar when he said time and space are equivalent with a conversion factor of c, implying c is dimensionless, based on scratch marks. Planck units were based on tick marks, not the 1983 definition of a meter. To claim the Planck length has to be defined by the new definition of a meter is circular logic and artificial because the new definition of a meter is based on the Planck length equation which was really based on tick marks. Relativity was an elucidation of the theory behind the Planck length equation L=cT but it too was derived and based on tick marks.

If you redefine meters while my c goes to 1/2 c in order to keep your c constant, then those things moving with a velocity relative to us, you will say, are now going twice as many of the new meters per second. And in both of our systems of meter measurement, the v/c ratio in relativistic equations will change for all objects moving relative to us. You would say v increased, but i would say c decreased, and in both views we would see the same real changes. Something moving at 0.6 c before the change would, in your view, now be moving at 1.2 c if there were no real changes.

I tried to make relativistic energy for rest and moving masses to remain the same before and after a change in c, while letting mass and velocity take on any values. What happens is that the the ratio of v/c has to stay be the same, which means velocities can only be measured relative to c, and that a change in c is not possible if both relativity and conservation of energy hold through a change in c.

well, i can say nothing that was not said before. one of us is missing something very fundamental, not just about the nature of measurement and physical experiment, but really about what is real. even though different physicists have different points-of-view on this, i think they all agree that dimensionless quantities are the only ones we really can perceive or measure. dimensionful physical quantities are always measured or perceived against a given standard of like dimension. for this reason Veneziano agrees with Duff "that all that matters are pure numbers." even though they disagree about other stuff. you are wrong when you say that the speed of light is a pure number if it ismeasured (as opposed to defined) by use of previously existing rods and clocks. the speed of light is not a pure number, it has dimension length/time. you are wrong that a hypothetical change in the speed of light in and of itself is anything that any of us beings (or atomic clocks) would notice as anything different. the universe does not set the speed of light. it simply is what it is, as paraphrased of Wilczek (he was talking about G, but the point is the same).
you should really post to sci.physics.research . it is a moderated newsgroup, but they will post anything that is really about physics. there are some real heavyweights there that can speak to your issue. i do not know exactly what they will say, but i doubt anyone there will tell you that a change in a dimensionful physical constant in and of itself is meaningful. we always measure these dimensionful quantities against another like dimensioned quantity and the result of the experiment (or our perception) is the ratio of these two quantities. always. r b-j 05:30, 26 Dec 2004 (UTC)

Since my relativity equations showed a change in c is absurrded, i'm less convinced of my position, but i need to rederive the the basic SR equations with a changing in c in an integral.

I believe it is probably simpler to detect if a real change has occured in a dimensionless number, but i don't know if c is dimensionless or not. Also, i think the measurement of a dimensionless constant almost always has to be carried out with instruments that measure dimensionful quantities, but the combination of those quantities based on theoretical equations is what determines the measurement of the dimensionless constant. Taking three different types of measurements concerning c and using theory to judge if c was the only thing that changed (and thereby proving c should be considered dimensionless) is doing the same thing. The first method includes the theory in the measurements, while the seconds applies the theory after the measurments are reported. This idea was touched upon in the first paper (which regards c as fundamental). - Scott

rbj what you miss is that it is not about the example of 2:1 changes, it is about sth that would be very fundamental (or perhaps only local still) plancK lengths for example, minimal potential, would change at the same rate as t or c, even entropy would then predict pK changes.It makes me wonder if pK is not just the maximum resolution of our thought. If something changes c it changes an aspect of pK we surely have no resolution for.80.57.67.243 (talk) 18:17, 27 November 2008 (UTC)

## C is just a human construct

We have to keep in mind that scientists who assigned dimensions to certain quantities to make them incompatible (Length, Time , Mass etc.) were not Gods and did not change the laws of physics by making such assignments.

There is no evidence whatsoever from modern physics that shows that dimensional quantities really exist. We certainly don't need them. C is just a conversion factor that arises because we have chosen to measure Length and Time in incompatible units. Variable C theories do exist but they can be mapped to theories in with only dimensionless parameters.

See here:

the creator of this article is aware of the Duff paper and has, indeed, put a link to it at the bottom. it's just that he doesn't really get it and is relying on the fact that other physicists have "rebutted" Duff as his justification for this latest version of cold fusion. i have tired of engaging him and am waiting for the sci.physics.research newsgroup to be reactivated (the moderators have not posted anything new for more than 5 days). r b-j 01:49, 4 Jan 2005 (UTC)

Rbj, I see the link now. I agree that sci.physics.research is a better place to discuss these issues. B.t.w. in the 18-th century people didn't know that heat and energy were the same thing. So, one could have argued that Joules and Calories should be given different dimensions and that the conversion factor is not dimensionless. Now what about a theory in which that conversion factor is space-time dependent? :)

Count Iblis 13:24, 4 Jan 2005 (UTC)

External link number 4 describes in detail how Duff was wrong and how the above comments are not relevant. Just as values were arbitrarily chosen for length, time, etc, so too were the concepts of length and time arbitrarily chosen as meaningful rather than "alpha units" and "proton ratios". God did not declare alpha to have special meaning in his heart any more than length or time. alpha comes out unitless only because we arbitrarily chose Length, Time, etc to have special meaning. I too tired of showing how each and every point RBJ made was wrong while he would not address hardly any of the counterpoints i made. I supplied a variety of references while he can only refer to Duff. In my continuing effort to dispell the bunk being posted here in the discussion area, i would like to address the point made above about the simple dimensioned conversion factor between Joules and calories. First of all, it's not a dimensioned constant, it's a dimensionless conversion factor that has units. Energy has only one dimension which is simply a (scalar) quantity that does not change with time in a closed system. There is a difference between units and dimensions, although the literature on the subject confuses the two. Yes, today's physicists can write a unitless conversion factor between space and time, namely i*c (although RBJ objects with that...as a partial reference, see Hawkin's "A Brief History of Time" in the index for "imaginary time". For more detail see the book he coauthored with Roger Penrose). But it is not a dimensionless conversion factor since space-time has 4 dimensions (hence vector quantities are needed for space and the "i" dimension is needed to specify time). If that conversion factor changes, then a big change to our ideas about physics is required. Likewise, if the conversion factor between joules and calories were observed to change, we would need to change some of our physics ideas. We currently believe Joules and Calories to be in the same dimension (i.e. energy) but measured in different units. If their relationship were observed to change, then it might require a different dimension. - Scott

## Serious POV problems

Ok, it's my understanding that VSL is not accepted by all, or even a majority of scientists. And yet the article makes no mention of this? There is something seriously wrong here. I would make the changes myself, but I sadly have little first hand knowledge of the issue. DaveTheRed 06:51, 18 Mar 2005 (UTC)

I do not know precisely how many physicists accept the theory. I do know that we can only measure dimensionless quantities in experiment or in our experience of reality. If ${\displaystyle c\ }$ or any other dimensionful "constant" changes without any of the dimensionless constants changing, then we would never know the difference. The claim that a possible change in ${\displaystyle \alpha ={\frac {e^{2}}{\hbar c4\pi \epsilon _{0}}}\ }$ is due to a change in ${\displaystyle c\ }$ is, as Michael Duff points out, simply a choice of what unit definitions you make. A change of ${\displaystyle \alpha \ }$ does have operational meaning whereas a change of ${\displaystyle c\ }$, in and of itself, does not.
I have suggested that this article be deleted, but have not gotten a single other wikipedian (some of whom have to be physicists) to second the motion. It does have serious POV problems, but I won't delete it without some "help". r b-j 16:31, 18 Mar 2005 (UTC)
I would probably argue against deletion, since VSL is an actual theory that some people subscribe to. It doesn't matter how valid the theory is, as long as there is prominent discussion about it in the scientific community, I think this article should be kept. But we really do need rewrite this from a NPOV. DaveTheRed 17:31, 18 Mar 2005 (UTC)
fine, i agree (about a rewrite), but it can't be me. i do not have an NPOV regarding VSL. i think it's cold fusion. i would recommend reading the Duff article cited at the bottom and the Duff, Okun, and Veneziano "trialogue" paper. i tried to put the dimensions and scaling issue in terms of Planck units. perhaps that can give you another POV. but i am not NPOV. r b-j 21:56, 18 Mar 2005 (UTC)

I agree with Rbj. The article should be rewritten. I won't be able to do it either. Actually, it may be worthwile to write an article for a peer reviewed journal about this issue. Duff uses too much string theory to argue his point. Once you accept that nature is formally describable, you also have to accept that ultimately no fundamentally incompatible quantities can exist. Any Theory of Everything can thus always be rewritten in terms of only dimensionless quantities. If you then define additional dimensional quantities and formulate a varying dimensional constants theory, that theory can be mapped to a varying dimensionless constants theory.

sorry Count, i didn't look at the history at first. i thought it was Scott, the creator if this article that left this note.
Duff doesn't use any string theory, not one spit, to argue his point. this has nothing to do with string theory. string theory is non-sequitur. i hardly understand string theory (really, just the pop stuff Brian Greene puts on Nova), but i fully understand the argument that, in reality, the only physical quantities that we measure, that we perceive, that make any difference to anything that involves us as human beings (or E.T. beings, for that matter) are dimensionless quantities. when something changes that affects us, ultimately it's a dimensionless measure, usually the ratio of like dimensioned quantities. we always measure a dimensionful quantity against another like dimensioned quantity.
if ${\displaystyle \alpha ={\frac {e^{2}}{\hbar c4\pi \epsilon _{0}}}\ }$ changed (let's say got bigger), conceptually, that would have meaning, the electromagnetic force (relative to the other fundamental interactions) would have changed in proportion (gotten a little bigger). then it would appear that the charge of an electron has gotten a little bigger (but it might not have) or that Planck's constant has gotten a little smaller (but it might not have) or that the speed of light has gotten a little smaller (that's the choice you and authors such as Moffat made) or even (if we're gonna say that ${\displaystyle c\ }$ might have changed) that the permittivity of free space has changed (like ${\displaystyle c\ }$, ${\displaystyle \epsilon _{0}\ }$ is defined in many measurement systems, such as SI or cgs). (i doubt anyone will argue that it's ${\displaystyle 4\ }$ or ${\displaystyle \pi \ }$ that has changed.) heck, someday soon (i would expect within a decade) ${\displaystyle \hbar \ }$ will be defined (because of a redefinition of the kilogram). if they do that, then a change in ${\displaystyle \alpha \ }$ gets blamed on a change of ${\displaystyle e\ }$, which still seems most natural to me, but that's my opinion. even so,. if they did that to ${\displaystyle \hbar \ }$ and ${\displaystyle \alpha \ }$ was measured to have changed, i would not argue that all of the electrons and protons and positrons in the universe have somehow transferred charge. i would say that they appear to have a different charge since their strength of their interaction has changed (which is fundamentally all a change in ${\displaystyle \alpha \ }$ can mean). that is all we would know or could ever know. to blame any conceptual change of ${\displaystyle \alpha \ }$ on a change of any of the dimensionful ingredients to it, is silly. r b-j 16:04, 19 Mar 2005 (UTC)

## minor change

Changed "theory of VSL" to "VSL hypothesis". VSL on its own is certainly not a scientific theory. Als changed "belive in" to "accept". Scientific theories and hypotheses are not "belived in" or not: they are "agreed with" or not. See Faith and Reason.

## VSL or CSL?

According to Einstein's GRT, the speed of light is variable in the sense that light speed is reduced near masses (remember, Huygens light bending around stars followed from it as well as his fame). IOW, it varies with position.Thus, wouldn't it be better to call the possible slowing down of light with time "Changing Speed of Light"? BTW, this has indeed nothing to do with units, even unitless values can be position dependent or time dependent. Harald88 22:08, 29 October 2005 (UTC)

of course it is conceivable that dimensionless "constants" might vary. and if they do vary sufficiently, we would know the difference.
i guess the question that someone like Duff might ask is, within Einstein's GRT, if that changing speed of light could be "operationally different" or, in my paraphrase, if such a change of c could be measured? it's always one Planck Length per Planck Time. if we measure it different with meter sticks and clocks, there would be a change in the number of Planck Lengths per meter stick or number of Planck Times per clock tick. is it that which GRT would predict near large masses? r b-j 22:36, 29 October 2005 (UTC)

## Link to c argument

Hi everyone. I'm new to Wikipedia. I've been engaged in a debate with Rbj about this varying c issue (see Planck Units - discussion page) and he invited me to look at this page. If anyone is still interested in the issue (anyone with stamina enough) you should check out our debate at Planck Units, starting under the heading 'Personal Opinion'. (How do I insert the link? Dunno).

Having seen the page here, I can well understand why Rbj is getting tired of repeating himself.

What was it The Terminator said?

"I need a holiday".

Thanks Rbj. Lucretius 08:53, 1 January 2006 (UTC)

hi Rod,
may i suggest that you register with WP and use your registered username to edit articles and to sign talk pages (with 4 tildes)?
reading the section you pointed out is meaningful and indicates that Albrecht and Magueijo are aware of the controversy and the reasons for why someone like Duff takes issue with them. they acknowledge that all we can measure and perceive are dimensionless quantities. good.
from what i understand in their argument in that section, it's sorta like this, suppose you detect a change in two or more dimensionless quantities, all that are some combination of physical "constants" like c, h, etc. some of these dimensionless quantities may have increased, others may have decreased, all by possibly different relative amounts. then what Albrecht and Magueijo want to do is choose a single factor of these multiple dimensionless quantities that would explain the measured variation of these two or more dimensionless "constants". am i reading that correctly? r b-j 19:46, 24 January 2006 (UTC)
BTW, i restored that deleted text (Dirac) that you put in (with a little formatting). it was not me who deleted it. r b-j 19:55, 24 January 2006 (UTC)

Rodolphe, i still wish you would register with Wikipedia and get a username. i dunno what i wrote to make you "glad", but, as far as i can understand the physics, if c (or h or G) varies without something like α varying, i don't think we would ever know the difference. if α varies, we would know the difference but the salient fact is that α changed, not c. can you address what i wrote above? am i representing Albrecht and Magueijo accurately? if not, can you correct it? if yes, can you tell me what other dimensionless quantity with c as a factor, other than α, is suspect to have changed? r b-j 17:35, 25 January 2006 (UTC)

Dear Rbj,

We may not see the difference between each constant if alpha was varying, i entirely agree with you but we definitely have to make a choice (each one is a possibility which i think make it interesting). By the way the paper (albrecht-magueijo), the varying c is tied to the cosmological frame (only a the very beginning of the universe). This is difficult to find any experiment to check this variation but it sounds more probable than the inflationary universe. User:Rodolphe

Rodolphe, thanks for getting a WP username. if you sign with 4 tildes (~~~~), it will timestamp your signature. Now if only α is shown to vary (no other dimensionless quantity), then i do not agree with you that "we definitely have to make a choice". in fact, i believe that if only α has changed, we must not make a choice between c, h, e, or ε0 or μ0. because there is no salient difference in the result. all we know is that the relative strength of E&M forces has changed (if α has changed).
I personally like these "rationalized" Planck units (same as Planck, but 4πG and ε0 are normalized instead of G and 4π ε0, but it's just a convention that i think is more natural). Anyway, those units are based only on properties of the vacuum and have absolutely no reference to any prototype, particle, or "thing". So then the unit charge is already defined before you start looking at particles. In terms of these rationalized Planck units, this elementary charge looks like √(4 π α) (or in Planck units it's √ α). Now from our POV, if we measure α to change, we think its because the elementary charge, e, has changed. So the reason that the strength of the EM field has changed is because the charge on all of these particles in some geometry has ostensibly changed. But that's only because of my preference in units. But it could be c or h, doesn't matter, it's all the same.
Now if you come up with a variety of different physical quantities (measured as dimensionless numbers) that combine c and h and e and whatever else, in independent ways (different powers on c or h or e) and they all have changed in such a way that the simplest plausible cause is c varying, then I would say you have a case going. r b-j 05:44, 26 January 2006 (UTC)

That is EXACTLY what Magueijo claims in his book (on page 199 of the U.S edition) he states "VSL was a theory of nature in which the simplest way to describe it was to choose units so that c (and possibly e or h) varied. To make it clear, John Barrow and I performed an interesting exercise in which we mathematically changed the units in our VSL theoy so that C became a constant. The result was such a long-winded mathematical mess that we believe our point was taken. A changing c, as the editor pointed out, was a choice or convention. But it was the right convention to adopt in the context of a theory based on contradicting relativity as ours was."
I am not a physicist, I'm a medical student, but I thought the book was put forth an interesting idea. Sure it hasn't been proven but neither have many other hypotheses in physics. Even if it turns out to be completely wrong it may still be of historic interest. There are many articles on wikipedia that are on theories that have been proven wrong like Phlogiston. I definitely think it meets the one Ossman criteria for a wikipedia article (see the David Ossman article)so I don't think the article should be removed. It should eventually be updated in a more indepth way by an expert as should all articles. I also can't seem to get the formatting right for this comment so I'm sorry if it causes confusion.Renwick 01:57, 9 April 2006 (UTC)

Light: Einstein's 1T 3D world re-think

Try 4T like this:

To start with, allow me, to question ...

Have anybody ever try to formulate the world in term of TIME, That is what if the physical world is represented by a FOUR dimensional T space? In such, every observer moves at the local speed of "light" in local reference frame, thus yield one of it's dimension INVISIBLE ! And make his Momentum in his REST Mass !

To start with: Assume some closely living, two dimensional creatures (Hs) , each are assembled of some basic units (M), and they measure their distance in term of time (T), normalized to C (his speed in light) . Clocks are placed at various locations for the measurement purpose. Each creature use a personalized clocks system, that calibrated to his origin to zero time, any clock at radial distance S should shows time "S" . Whereas S = sqrt(t2^2 + t3^2) , such ( t2, t3) is the time plane .

What If in fact that, this is a three Dimensional space, with the axis t1 orthrogonal to the planes. Some super 3-D creature MrChung (MC) move this plane along this t1 axis, say, at a parametic displacement d(t3)/dg, then all of those clocks in the time plane would registrated a S + dt(t3)/dg mysteriously.

While those clocks measure faithfully the real displace in 3 Dimension, the plane would experience a "flow of time". As a matter of fact , a clock that "relocate" ds on the plane while the plane have a t1 dispalcement of d(t1) would show a time change of sqrt( ds^2 + d(t1)^2 ). The "speed" of that clock on his plane would show V= ds/ d(t1).

In otherword, An misterious, time flow (t), location change (ds) and volocity (ds/dt) relationship exists. The funny thing about it is the upward Volocity, regardless of how MC move it, is ALWAYs = C = 1. It's also interesting to point out, for this creature, physic, that related to time, is controlled by the MC, "move" of his plane to create the personal time "flow". Otherwise, his world will be a frozen world.

In this world, a H see all other Hs that are built by the same units, and in close vicinity. What if MC tell H(M)s that their world is just some plane with a Third dimemsion t1 ? What if MC tell H(M)s that MC has his own 3 Dimensions that is called C = [j0, j1, j2] ? What if MC tell H(M)s that M moving at a rate, proportional a personal P , a vector of size |P| ?

In other word, MC said, "each H is a moving time plane, T in C .", MC also said: 1) The P is a gereralized momentum, happened to be the momentum of M, because C is normalized, is also a normalized M. 2) Each H carries his own T plane, T planes are differently scales, ratioed by the |P|.

GR / SR are buildin.

[More on Light and Time] I have a link to http://www.humancafe.com/discus/messages/6/7.html?1138085434

Where I shall propose an objective Universe.

## rewrite

This article has needed expert attention for some time. I finally got sick of the anonymous editor frequently removing the tag (and any references critical of VSL cosmology!) so I just sat down and did the rewrite myself since I have some knowledge of this area. I removed a lot of material that seemed to me to be original research, unsourced, irrelevant or extraneous, and added some new material in, including extensive referencing. Please let me know what you think. I removed the links section, as it mostly duplicated the references, and I also removed the see also, since it principally duplicated things linked in the main text. –Joke 02:08, 18 May 2006 (UTC)

I like this rewrite. Especially adding the section of what theoretical physicists call "condensed phase" and most mortals call simply (but not as precisely) matter. I did a little copyediting in the section, correcting one spelling error and adding one forgotten phase of matter (I did not add plasma not to complicate the sentence too much) plus Wikifying. By the way, people working in applied physics like me usually reference the variable speed of light in condensed matter as the refractive index. Therefore, I added a link to it. Friendly Neighbour 07:24, 18 May 2006 (UTC)

Good rewrite, Joke! One remaining problem from the old version are the virtual photons. The virtual photons are mentioned in the third sentence of the article but only much later do we read that: "Feynman diagrams and virtual photons are usually interpreted not as a physical picture of what is actually taking place, but rather as a convenient calculational tool (which, in some cases, happen to involve faster-than-light velocity vectors).". I think that we should mention the virtual photons later on in the article and make it clear immediately that they are just a calculational tool.

Also, instead of focussing on virtual photons so much, we could mention the Scharnhorst effect. In a recent article it was pointed out that this does not lead to causality violations, see here. Count Iblis 12:15, 18 May 2006 (UTC)

We already have an article on Scharnhorst Effect so only a sentence or two with this link are probably enough. The Liberati et al. 2002 paper is also mentioned there. Friendly Neighbour 13:29, 18 May 2006 (UTC)
Yes, I added that article there just a few hours ago :) Count Iblis 14:05, 18 May 2006 (UTC)
i've sent my kudos to his talk page. but i am also happy with the rewrite. r b-j 15:34, 18 May 2006 (UTC)

Thanks all for the praise! I've tried to clarify a couple thinks and added a link to the Scharnhorst effect. If someone wants to add a sentence or two about it, please do. –Joke 16:38, 18 May 2006 (UTC)

## IP anons

The article was vandalized (this was promptly reverted) by 71.142.177.64 (talk · contribs) (Southwestern Bell Internet Services, possibly geolocated near San Diego, CA). ---CH 21:05, 4 June 2006 (UTC)

The speed of light limits how fast one can revert vandalism :) Count Iblis 22:34, 4 June 2006 (UTC)

## Petit: lack of notability

I erased all references to Petit. He does not meet any of the criteria for WP:Notability (academics). E.g., his citation record is exceedingly poor: 4 citations for all of his published papers, according to the SPIRES data base. —Preceding unsigned comment added by 137.138.201.73 (talk) 02:02, 15 July 2008 (UTC)

Reverted modifications from this anonymous IP. The guidelines in WP:Notability (academics) say the number of citations of a paper is only a rough estimation of its 'importance'. But yet the reference to Petit's paper is here mainly because he was the first to introduce a variable speed of light cosmology, so it his just a right to anteriority. Moreover considering:
- 4 papers were the first published on the subject (as just stated)
- these papers were published in academic journals, through peer review (Modern Physics Letters A, International Journal of Modern Physics D)
- each paper has a reference to a linked source
- the papers are written by additional coworkers
Since you think citations are a problem, I added the following sentence in the article:
"However it should be noted that while this was the first VSL model to be published, and the sole to date where an evolution law is given relating the joint variations of constants through time while leaving the physics unchanged, these papers received few citations in the later VSL litterature."
Tokamac (talk) 19:16, 13 August 2008 (UTC)

## Virtual photons

Virtual anything can travel faster than c, and that is physics--- it's not just a property of the calculational method. Any way of defining a "photon" (or any other particle) as a localized object in relativity which cannot travel outside the light-cone fails. The right statement of causality in field theory is that the commutator of fields are zero when the fields are spacelike separated.

But this whole article goes on and on about photons and light, as if that has anything to do with "c" the constant. But "c" as a physical constant has nothing particularly to do with light, except as an accident of history. It could have also been called the speed of gravity, the maximum speed of electrons, neutrinos, anything. So to obsess about light in relation to c is entirely out of place.

I think that the theory that "c" changes (which presumably means that a whole set of dimensionless constants change together in a certain way) should be separated from the physics of light, and made to stand on its own wobbly legs.Likebox (talk) 23:01, 23 September 2008 (UTC)

==Exit velocity. The index of refraction of a diamond is approx 2,5 and thus thus the calculated light velocity through the diamond is about 0.4c. I can understand how it can be argued that the light path through the diamond is bent and the velocity accordingly reduced. What I dont understand is how the light is bent the same angle on exit as it was on entry, but the velocity has suddenly (and marvelously) changed back to approximately c. But nobody likes the alternate concept of a c value zigzag path through the diamond as a way of explaining this. Where am I irrational? WFPMWFPM (talk) 23:49, 23 October 2008 (UTC)

I like it, C atoms would suggest a block path? the measurable effect is the same, density slows light80.57.67.243 (talk) 18:30, 27 November 2008 (UTC)

## Time Roots

I start thinking about the VSL theory and i imagine the time as a curve. If c been 60 magnitudes faster in the begin than this is a curve, right? But as i understand it everything changes with it and so even if c is variable the hall surrounding is always realitve? How would a spacecraft look alike? Could i imagine a vacuum bubble filled with a spacecraft which starts the engine and gets faster - traveling in vaccuum beyond light speed hence the surrounding relativity no longer effects the bubble? --Tales23 (talk) 01:09, 18 January 2009 (UTC)

## Space and time are equivalent?

The introduction to this article includes the sentence "A fundamental change to relativity is needed if c is changing because relativity shows that space and time are equivalent." I understand a little bit about special relativity and how the concepts of space and time are intertwined. But it seems misleading to say the two concepts are "equivalent". I'm not sure how to reword this so that (a) those with a better technical understanding of physics will approve, and (b) the layman will not balk and doubt (see WP:ASTONISH). Would someone with a strong physics background care to comment, with a view to rewording this? CosineKitty (talk) 19:45, 27 January 2010 (UTC)

I've changed it to make it clearer. It's not just relativity but much of physics that depends on a constant c, some as it relates closely to the speed of light – electromagnetism for example – and some as its set in Spacetime, the 4D space which the geometry of depends on the speed of light. This is fairly standard physics but there's also a reference which ties it all together.--JohnBlackburnewordsdeeds 18:55, 28 January 2010 (UTC)
Thanks, JohnBlackburne! Your change gets the point across quite well, and I believe will create less cognitive dissonance for readers who are not as familiar with physics. Adding the citation was a nice bonus. CosineKitty (talk) 19:30, 28 January 2010 (UTC)

## Photon mass is compatible with renormalizability

It was known to all the principal investigators of QED in the 1950's that the photon could be massive in QED keeping everything renormalizable. The reason is that in the massive propagator has two parts, one proportional to g_uv, the other proportional to k_uk_v, the second part spoils renormalizability, but it is zero for every QED process because of conservation of charge--- the photon always couples to transverse sources.

This is why 'tHooft's discovery of the non-renormalizability of massive Yang-Mills theory was such a surprise. From the well understood example of QED, Schwinger, Feynman, and all the others just assumed that the same thing would work in Yang Mills. But in Yang Mills, the current is only covariantly conserved, meaning there is self-interaction of the spin-1 particles, and this does not allow the same argument to go through.

The issue can be clarified completely by considering a Higgs mechanism for U(1) with a scalar phi of charge "e" and VEV V. In this case (but only in this case), it is possible to take the limit that e goes to zero and V goes to infinity in such a way that the Higgs boson for the U(1) becomes infinitely massive, but the mass of the U(1) photon stays fixed. The same mechanism will work in the standard model to give the photon any mass you want. This is the "Affine Higgs mechanism" discovered by Stueckelberg.

This method doesn't work for nonabelian Yang Mills theory, because charges are representations of the group, and they are quantized. Likewise, you can't do this for a compact U(1) (meaning with quantized charges or with magnetic monopoles). So the correct statement is that a massive photon is not consistent with the standard model, assuming the standard model U(1) is compact. This is a very natural assumption, so there is no need to worry. But historically, Feynman would worry about the photon having a galactic-scale mass.Likebox (talk) 23:35, 28 January 2010 (UTC)

## Section with original research and link to own published work

P. Smeulders added a section, referenced by own published work. Isn't this wp:COI, and, unless some secondary source can be provided, quite orthogonal to our wp:NOR policy? - DVdm (talk) 19:28, 28 February 2010 (UTC)

It does look like conflict of interest to me. Plus it appears to be a re-emergence of the controversy that happened at Speed of light. The claim that a hypothetical change in the speed of light couldn't be detected is faulty: it assumes that a meter stick used to measure c is always in sync with the 1983 SI definition that ties the meter to the speed of light. It is true that someone trying to prove that electromagnetic radiation travels at a variable speed would have to be careful to avoid using the radiation itself as a distance measure in the same experiment, but the flat wording presented here does not seem to hold water: "It is impossible to measure the speed of light correctly at all". CosineKitty (talk) 21:03, 28 February 2010 (UTC)
Yes, the claim is trivially faulty - we know that since ages - but the fact that the source is nonsense doesn't really matter, as Wikipedia is not about thuth, but about sources. So we need a reliable secondary source. I have removed the section. Let's see whether a reliable secondary somehow emerges. DVdm (talk) 21:24, 28 February 2010 (UTC)

I would like just to correct the above: I did not mean the meter as defined by the speed of light. Any measurement of this speed must use an instrument that is in principle related to the classical meter in Paris. And it is this meter that is proportional to the speed of light ( if the fine-structure constant is real constant!). And this then makes any direct measurement of the speed of light a flawed measurement. The need then for a VSL is for instance coming from the supernovae data. —Preceding unsigned comment added by 86.151.152.159 (talk) 12:07, 1 March 2010 (UTC)

## Observations by Fermi

In 2009 Fermin conducted few observation of gamma ray bursts, and noticed that fotons which traveled 8 bilion lat years, have appeared in the same second (there were about 700 ms delay beetwen short and long X rays, which means about 10^6 of energy difference. So essentially speed is light is constant with respect to varying wavelenght! Spectacular. this 700ms is essentially 0, as there can be many other explanation for such small difference. This automatically falsified many theories which claimed that there is a strong depenednce on speed with respect to the energy. On http://svs.gsfc.nasa.gov/vis/a010000/a010400/a010489/index.html one can find further informations.

## What does this phrase mean?

"While it is usually thought that no meaning can be ascribed to a dimensional quantity"

Wtf does that mean???? Fresheneesz (talk) 00:32, 1 May 2011 (UTC)

## Omission of Einstein's 1911 attempts on a variable speed of light

A serious drawback of the whole article is the omission of Einstein's 1911 attempts on a VSL (while he worked on General Relativity). It is well documented in some Annalen der Physik papers. As a consequence, some statements in the article seem untenable. — Preceding unsigned comment added by 84.151.216.6 (talk) 09:41, 11 November 2012 (UTC)

## Rewrite needed

The article needs a rewrite. I plan to do this, with the following intentions:

- to make clear VSL applies to different things, of which some are just details of mainstream physics, some others alternative concepts

- to make clear that VSL theories are a matter of debate

- to give a proper history of VSL attempts (which does not start in 1990, but in 1911)

- to make clear the relations to other constants

- to give a reasonable structure to the article

Minor points are:

- Barrow' quote is very long

- Too much about Petit's VSL theory. This is not a place to give a summary of it. Irrelevant stuff about how the theory was received.

- this is not a place for an extensive discussion on other varying constants

I'll try to include however all the relavant information If you have objections or suggestions, please comment here. — Preceding unsigned comment added by ClassicalPhysicist (talkcontribs) 22:38, 12 January 2013 (UTC)

Well, feel free to be wp:bold. The worst that can happen is that it gets reverted. Well, I guess it can get worse; an edit war could get started.
Personally I think your major points are fine and I would say go ahead. I would leave the Barrow quote alone. It's a single paragraph that makes this important point in a book dedicated to the concept of fundamental constants of nature. I'm of the opinion that there is no meaningful concept of variation of c as long as it's defined to be a particular constant of meters per second. 71.169.181.144 (talk) 22:52, 12 January 2013 (UTC)

- The above statement is fallacious if a variation in c is not meaningful in a proper defined theory, one can say all the other laws of physics are meaningless.

Hi, first I might suggest learning how Wikipedia talk pages are done. How to format and align comments and also what the talk page content should be. And even if you're an anonymous IP (like me), you should sign your comments or a bot will end up doing it for you.
Second, I might suggest looking at the Fundamental constants page and reading the Barrow book (if you can get it) and perhaps John Baez's page about it . You need to understand the fundamental difference between a dimensionful constant of nature (which is, essentially, an expression of the units used to express it) and a dimensionless constant (which is not affected by whatever system of units one chooses to use). Maybe also take a look at the Planck units page. 71.169.184.73 (talk) 15:48, 23 January 2013 (UTC)

## Creationist "CDK" nonsense

Isn't the creationist "CDK" (short for "speed of light decay") at least as notable as Albrecht-Maguello's VSL?

Let me start out by saying that CDK is nonsense. Setterfield started off with 3 points (to make 23 Oct 4004 BC the Big Bang, 29 Oct 4004 BC the date of the oldest known homo sapiens fossil, and 1987 to 1987) and tried to fit a curve that fell within the error bars of every c measurement over the past few centuries. He found one that fit, and declared that a theory that the speed of light decays and therefore not only the Bible but even Ussher's chronology are in perfect accord with science and in fact predicted it in advance. Over the next few years, he published new curves (including a cubic curve that had the speed of light gradually speeding up again through much of modern history and then slowing down again around 1980) before he apparently gave up trying to keep up with better measurements.

Even years after ICR recommended that creationists stop pushing CDK, there are clearly tons of people still writing about it and searching the internet for it. I realize Google results aren't everything, but they're not _nothing_. And a quick search for "variable speed of light" turns up, other than this article, a lot more pages about CDK than about the Albrecht-Maguello papers. In fact, 5 of the 6 mentions of either of their names come either from creationists claiming that Maguello's theory supports them, skeptics carefully distinguishing Maguello from the creationists and then never mentioning him again, or skeptics lumping him in with the creationists as a crackpot. (There is a bit more if you count the Urban and Kiritsis-Alexander ideas as related to Maguello, but since this article doesn't cover those at all, that doesn't really help.)

So, I think this article should at the very least include a section mentioning CDK, that it's superficially similar but not the same thing, and that the results of Moffat, Maguello, and their successors do not support CDK. --213.115.171.131 (talk) 19:06, 4 October 2014 (UTC)

## Einstein's view

Now that the Einstein digital papers are online, it's possible to search various papers to determine Einstein's opinion about the speed of light. For example you can find this where in the second paragraph Einstein says this:

"Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields".

That wasn't written in 1911. It was written in 1920. I'm afraid it's a popscience myth, or a rewriting of history, to claim that Einstein abandoned the variable speed of light in 1911. You can find other examples yourself. Note that in some of the translations you see the word "velocity" instead of "speed". Some will tell you that this is the vector quantity velocity. It isn't, it's the common usage, as per high-velocity bullet. Have a read of this Baez article written by Don Koks for another example. See the general relativity section. JohnDuffield (talk) 19:14, 2 January 2015 (UTC)

All you need to do is look at the math in Einstein’s book "The Meaning of Relativity" 5th edition from 1953. A calculation of alpha (α) follows equation 107 and makes an unambiguous use of variable scalar light velocity (L) both as the argument of a partial differential function (proving a variable) and as the denominator in a fraction (proving not a vector) both in the same integrated quantity. Division by a vector is not defined, so there is no other way to interpret the velocity of light in this usage except as a variable scalar speed.

(1/L)(∂L/∂x1)dx3

In other calculations Einstein explained that he used velocity as a vector when it was measured as components of a coordinate system.

Peter Bergmann did not agree with Einstein, but left the dispute out of his earlier book "Introduction to the Theory of Relativity" 1942 to get Einstein’s endorsement. After Einstein died Bergmann wrote a new book "The Riddle of Gravitation" 1968 claiming that vector light velocity could change direction but not speed. This has become a prevailing opinion in science, but not in agreement with Einstein’s unambiguous math.

Max Born agreed with Einstein and very clearly stated both speed and direction of light change in a gravity field. Einstein’s Theory of Relativity 1923 in English, 1920 in German. Dover editions 1965 page 357. Astrojed (talk) 01:43, 24 June 2015 (UTC)

## Conflation of unrelated concepts

This article is aware in some places, and unaware at others, that "VSL" groups a number of completely unrelated proposal. This is of course a result of content-creep over time. Atm, I can see at least three unrelated topics here:

• "Einstein and Dicke" ideas of frequency/wavelength dependency of c: all criticism related to "but c is dimensionful" is off topic to this, because it is about an upper limit on the ratio of c of light of two different frequencies. If c were frequency-dependent, the SI definition would become meaningless unless a specific frequency was specified.
• massive photons: this is not a proposal that c as a fundamental parameter in relativity etc. is variable, but that actual light travels at variable speeds slightly below c. Again, this would be about the ratio of the speed of a given photon to c
• cosmological things: Here I am not sure whether "VSL" is just a convenient way of phrasing this for the purposes of cosmologists who are perfectly aware that their "variable c" is equivalent to a variation of alpha and/or G. The problem is apparently that the editors responsible for this section were themselves not sure/aware of this.

tl;dr / bottom line: it is useful to point out the "dimensionful" problem to the reader of the article, but it is beside the point to portray this as a "criticism" because it simply doesn't apply to any actual proposals discussed in the article. It also isn't possible to present any one "criticism of the VSL concept" because there isn't any single "VSL concept". --dab (𒁳) 13:58, 12 May 2016 (UTC)

## Sign error in Dicke's refraction formula?

If c_0 is the speed of light absent of gravity, should not c --- the speed of light in presence of gravity --- be smaller? The formula then should rather have a minus sign as in 1-2GM/rc^2, converging nicely to 0 as r approaches the Schwarzschild radius r_s=2GM/c^2 from above? — Preceding unsigned comment added by 46.92.251.76 (talk) 08:20, 17 September 2017 (UTC)