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Can C be relative?

  1. Aug 15, 2006 #1
    Ever since Prof. Davies paper suggesting that the speed of light has changed was published I have been playing with some figures and would like to get some opinions.

    We all accept that time is relative, if speed is V=d/t then velocity (speed) is dependent on our unit of time in this instance the speed of light is actually the speed at which we are travelling through time, or am I missing something?
  2. jcsd
  3. Aug 15, 2006 #2


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    You are putting the cart before the horse, and turned the effect into the cause.

    Look at the postulate of SR. You'll see clearly that (i) c is a constant in all inertial reference frame and (ii) time dilation is NOT part of the postulate. This means that the starting point here is the constancy of the speed of light, and one of the consequences of that postulate is the time dilation effect.

    I'm sure you can see now why turning the tail end back into the head, and using the effect to change the cause, does not really make any sense.

    As for Davis's claim, it is still highly controversial (I've listed several recent publications that contradict this on here), and it has more to do with the fine-structure constant that might have changed over time than anything else. Even if this is true, it is still a major jump from the fine structure constant changing to c changing with time.

  4. Aug 16, 2006 #3
    Well in all fairness ZapperZ you really cannot derive the Lorentz factor from the postulate of the constancy of the speed of light alone. That is simply a mathematical impossibility.
  5. Aug 16, 2006 #4


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    Where did I say one could?

  6. Aug 16, 2006 #5


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    Is it simpler to deduce the constancy of time?
  7. Aug 17, 2006 #6


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    it, to say the least, is controversial. i'm more of the mind of Michael Duff, who, in my opinion blew Davies' claim out of the water with a very sensible fundamental argument that Davies is confusing choice of units with meaningful reality in physics:

    from: http://www.arxiv.org/abs/hep-th/0208093

    when we measure or perceive anything, we are measuring dimensionless numbers. we are measuring or perceiving one (usually dimensionful) physical quantity against a like dimensioned standard (sometimes called a "unit"). a variation in the fine-structure constant, [itex]\alpha[/itex] or the ratio of particle masses (such as [itex]m_p/m_e[/itex]) is something that has operationally meaningful consequence. the variation of a single dimensionful quantity, in and of itself, does not. and blaming any conceivable variation in a dimensionless "constant" such as [itex]\alpha[/itex] on any single component, is not meaningful. if [itex]\alpha[/itex] has changed, there is no meaningful differentiation between saying it because of changing [itex]e[/itex] or [itex]c[/itex] or [itex]\hbar[/itex]. we cannot know.
    Last edited: Aug 17, 2006
  8. Aug 20, 2006 #7
    We can add that it is a fact that can permit and even predict some versions of theories like LQG and other. If my memory is not so bad, some people in the Imperial College were working on the possibility of light traveling at different velocities (acording to the energy carried), I'm not sure that Fortini Markopolu examined the idea there, but some people considered the implications and even the possibilty of experimental detection of it -the effect becomes accumulative for long cosmological distances for the calculations in LQG-. I don't know if that was the idea when tzemach started the post. If it was the case, resulted inaforutnated the metion of Davies.
  9. Aug 22, 2006 #8

    You only need two principles. The constancy of the speed of light and the principle that the laws of physics are the same for all inertial observers (i.e., observers agree on events). That and some algebra.
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