Speed of light not constant?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by sculptor, Nov 30, 2016.

  1. sculptor Valued Senior Member

    If the speed of light is not constant, how many theories fall by the wayside?
    Expansion seems a likely candidate?
    One theory holds that when the universe was young, it was so hot that the speed of light was almost infinitely fast = faster than gravity waves = what we think we see is grossly misunderstood.

    Your thoughts?
    danshawen likes this.
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  3. Janus58 Valued Senior Member

    If light traveled faster in the past, Then either c has changed over time(meaning the universal speed limit has changed), or this limit doesn't exist(which seems unlikely since all our experiments to date supports the idea.) If it's the first, gravitational waves travel at c so they would have traveled as fast as light in the past, the same as now. And if its the second, why should we assume that gravitational waves adhered to a speed limit that didn't exist; what kept gravitational waves from traveling as fast as light back then? Put another way, if light traveled faster in the past, but gravitational waves didn't, then it seems the oddest of coincidences that we now live in the universe when they just happen to travel at the same speed.
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  5. sculptor Valued Senior Member

    Aye, there's the rub.
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  7. Ophiolite Valued Senior Member

    Superficially informative.
    Fundamentally obfuscating.
    Inherently passive aggressive.
  8. sculptor Valued Senior Member

    Actually, just voicing ignorance and confusion as/re "coincidence".
    If A and B occur independent of each other, that's coincidence, which I suspect is very rare.
    Or: A could be caused by B
    Or: B could be caused by A
    Or: There may be an unknown unifying and causal factor C
    Or: There may be several unknown unifying and causal factors C,D,E,F, ... etc.

    Did you have any useful incites that would qualify or quantify the seeming "coincidence"?
    Or, did you post for an unrelated purpose?

    back to the op
    If C is variable, or has been variable, then our observations may be inaccurate. It would most likely then follow that theories based on those observations become suspect.
  9. origin Trump is the best argument against a democracy. Valued Senior Member

    The point you may be missing is that gravitational waves travel at c (not 'C'). If the speed of light was faster in the olden days then the gravitaional waves would have moved faster (at c).
    Sure. If the underlying basis of a theory is incorrect then the theory is suspect. No surprise there.

    All of the information we currently have would indicate the speed of light has always been c, so this is just sort of an idle speculation.
  10. sculptor Valued Senior Member

    This is way outside my areas of expertise, so, for me anyway idle speculation indeed.

    I was reading of João Magueijo, and Niayesh Afshordi, who proposed something different.
    They propose that light tore along at infinite speed at the birth of the universe when the temperature of the cosmos was ten thousand trillion trillion celsius.
    Magueijo and Afshordi came up with their theory to explain why the cosmos looks much the same over vast distances. To be so uniform, light rays must have reached every corner of the cosmos, otherwise some regions would be cooler and more dense than others. But even moving at 1bn km/h, light was not travelling fast enough to spread so far and even out the universe’s temperature differences.
    Just an untested theory, but rather interesting
    ergo my query.
  11. Ophiolite Valued Senior Member

    Like you I was going for the incite rather than the insight.
  12. sculptor Valued Senior Member

    As expected.
  13. Fraggle Rocker Staff Member

    The speed of light is constant in a vacuum. This is its maximum velocity. But it is slower in other media.
  14. sculptor Valued Senior Member

    That certainly is the current assumption and coincides with current measurements.

    Magueijo and Afshordi seem to think that the speed was not constant during the early days of the universe.

    I have no understanding of how, exactly, they intend to test their hypothesis
    ergo this op.
  15. danshawen Valued Senior Member

    What if the speed of "at rest" in all inertial reference frames isn't constant? Because this is EXACTLY the same question, and it does have an answer that demonstrates it is an equivalent question.

    What if time dilation is dependent on relative motion or proximity to gravitational fields? What if this dilation is really more dependent on the speed of "at rest" than it is on the speed of light, the speed of "at rest" and the origin of inertia 'energy' itself in a given direction being related to the tensor sum of +/- c?

    What if a "fixed point" coordinate origin in space is fictional because each of three linear dimensions is 100% time, not some Pythagorean complex mixture of Ancient Greek ideas about geometric solids that aren't solid at all? What if the only 'origin' of absolute space and of the current instant of time is at the geometric centers of individual particles of matter and the space between them simply light travel time?

    What if quantum spin related to entanglement is faster than light and this is what distinguishes quantum effects from relativistic ones? What if a boson with a spin of zero is as vital to understanding physics as "at rest" is, and for the same reason the speed of light invariance is important to understanding relativity?

    A question appropriate to a sculptor, don't you think?
    Last edited: Dec 3, 2016
  16. rpenner Fully Wired Staff Member

    Wrong question. For if the local speed of light in vacuum was not constant as predicted by Maxwell's Electromagnetism, Quantum Electrodynamics, Quantum Field Theory, and General and Special Relativity, those historically successful physical theories would be incompatible with some observations. But this is not the case so those theories won't be discarded even if later evidence shows that many billions of years ago, or at very tiny scales or to a very slight degree the speed of light changes, as that means for all practical purposes now the speed of light is the same so they are good theories for predicting the behavior of the vast majority of phenomena at the precisions that we have tolerated for hundreds of years.

    So your question should be "If the speed of light is not constant, how many observations would show that and how?" and that requires you to develop a hypothesis of how much the speed of light changes, when it changes and how it changes. You can even say "I don't know" and put a unknown parameter into those places. Such a hypothesis is called a test theory and is compared with observation. For example, if photons had mass and special relativity was correct then there would be a slight amount of dispersion in the vacuum and distant stars would look like rainbow streaks due to proper motion. This doesn't happen so the mass of the photon must be very tiny compared to the energy scale of visible light. That test theory was tried in a sophisticated way http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.043901 . Another effect is that magnetism would drop off at a faster rate than predicted by Maxwell's equations. That was compared with astrophysical observations of the solar wind with the conclusion that the scale of drop off (if any) was at least 1.3 AU so the photon mass (if any) could be at most 0.0000000000000000000000015 times that of the electron. http://www.phy.pku.edu.cn/~qhcao/resources/class/Part_14_Fall/lit_Photon_mass.pdf

    Citation required by forum rules.
    Are you referring to this? https://journals.aps.org/prd/abstract/10.1103/PhysRevD.94.101301 ( also at https://arxiv.org/abs/1603.03312 )

    It's a radical proposal going far beyond just saying gravity and light had different speeds in the very early big bang. They say there were two time dimensions and two varying cosmological constants tied to an unknown quantum field that we just don't see nowadays. (Scaffolding.)

    Not "days" but fraction of a second.
    They are proposing an alternative to inflation, with no specific test to distinguish it from inflation. But if future research favors their specific prediction for the spectral index of primordial density fluctuations their hypothesis may become favored. But just because the universe we see today might be compatible with scaffolding doesn't prove that there was scaffolding of the specific type listed.

    As for how this would impact existing theories: Since the scaffolding is gone, they are saying all tests today would be compatible with General Relativity. If they were proven correct (which will require decades of expensive observation) there would be no impact on current theories other than knowing that General Relativity and Quantum Field Theory are not the end of physics. Future work would focus on looking for reconciling General Relativity and Quantum Field Theory and the scaffolding into a single framework compatible with observation, a situation little changed from today.
    Last edited: Dec 3, 2016
  17. ajanta Registered Senior Member

    Light speed is constant but it is really fishy to me, because at light speed an imaginable clock should tick 0 second on photon's reference frame but then how can photon's electric field changes its value (+/-) at 0 second ? Is time dilation wrong on photon's reference frame OR c is not constant ?

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  18. Janus58 Valued Senior Member

    No, the time rate for a clock traveling a c is undefined. Look at the time dilation formula.

    T= t/sqrt(1-v^2/c^2)

    At v=c you get T=t/0. Division by zero is undefined

    The fact that the above equation approaches infinity as v approaches c, doe not equate to equaling infinity when v=c.

    Also your view of the electric field changing its value is off also. The variation we see is due to the passing of the various parts of the electromagnetic waves. To see what I mean, do the following experiment. Draw a representation of a sine wave on a piece of paper. Now cover it with a blank sheet (or better yet, a sheet of graph paper. Now slide the lower paper with the sine wave along the direction of the wave so as you go along you expose more and more of the wave. As you do so note what happens to the point where the line of the wave intersects with the edge of the upper paper. It moves up and down as you slide the lower paper. That intersection represents the oscillation we see in a passing light wave. The sine wave you drew isn't vibrating up and down.
    danshawen likes this.
  19. Ophiolite Valued Senior Member

    The reason I frequently attack you is simple: you post fatuous nonsense and try to dress it up as sophisticated thinking. This offends me.

    You really need to consult your dictionary, reflect on the meaning of "assumption", then recognise how monumentally foolish your post was.
  20. sculptor Valued Senior Member

    I think, John galt, that you have chosen to take offense when none was given.

    I was not the source, that distinction belongs to Magueijo and Afshordi.
    I posted their hypothesis here to see what other people thought of it, and it's likelihood and ramifications.
    (when I finish with "Your thoughts", that's usually a dead give away)

    That is what you should have been responding to.
    (I keep hoping that you're gonna get better)
  21. Ophiolite Valued Senior Member

    So, we shall have to disagree. You think posting fatuous nonsense is not offensive. I think it is.

    I've just remembered there is an Ignore button.
  22. sculptor Valued Senior Member

    Do that John, you may be less unhappy.

    Magueijo and Afshordi?
  23. sculptor Valued Senior Member

    (I do not remember where I first read the article that fostered this op-----but here are some links)





    just search: Magueijo and Afshordi

    (pardon delay---harvested another deer and been skinning and butchering , packaging for freezer, ...and .......feasting on some very fresh meat...)(It's snowing now, so tracking the elusive beasties is gonna get easier)
    Last edited: Dec 4, 2016

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