The Speed of Light is Not Constant

Discussion in 'Alternative Theories' started by Farsight, Feb 23, 2014.

  1. Farsight

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    But they are employed in relativity, for example in explaining SR time dilation, see wiki.

    It isn't. It's the frequency of the light. Only in the NIST caesium clock used to define the second, we can't refer to frequency because frequency is cycles per second.

    And something is going slower when the clock is lower. What do you think it might be? A rivulet of time flowing through the innards of those clocks?

    No problem.

    Again no problem.

    I'm not misinterpreting it. Einstein and the evidence are on my side. Now come on, something is going slower when the clock is lower. What do you think it might be? A rivulet of time flowing through the innards of the clock?
     
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  3. Farsight

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    Well said, RJ. But look at the OP. People are rejecting what Einstein said.

    I'm afraid it is about light. See what I said to OnlyMe. Something is going slower when the clock is lower, and there is no rivulet of time flowing through the innards of the clock. What is inside the clock is light, moving.

    Thanks nimbus.
     
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  5. Farsight

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    It isn't misleading at all! Two clocks at different altitudes run at different rates. The lower clock goes slower. That's it. It can't be simpler.

    Oh waffle. It isn't "meaningless in relativity". Relativity predicts that the clock goes slower when it's lower!

    I beg to differ. If I dangle you on a cable above a black hole, you are time dilated. If I let go, you're still time dilated.

    I understand it, Einstein and the evidence are on my side. I can explain it, and you can't counter it. I am the expert now. Get used to it.
     
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  7. Trippy ALEA IACTA EST Staff Member

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    And what's the inverse of cycles per second? Seconds per cycle. So you define one second as being some exact number of cycles.
     
  8. Farsight

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    The second is defined to be the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. It's periods of radiation. Not hyperfine transitions. It's like you're sitting in a little boat riding up and down and counting the waves that pass you by. You count 9,192,631,770 of 'em, then you say that's a second. Then the frequency of those waves is 9,192,631,770 Hertz by definition.

    The important point to note is that you define your second using the motion of light, and you define your metre using the motion of light too. It's the length of the path travelled by light in vacuum during a time interval of 1/299,792,458th of a second. Then you use the second and the metre to "measure" the local speed of light. But you aren't really measuring it. You've defined it to be 299,792,458 m/s. The constant speed of light is a tautology. Make sure you read the time travel is science fiction OP to understand the OP of this thread. There is no time flowing in a light clock.
     
  9. Trippy ALEA IACTA EST Staff Member

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    This is simply untrue.

    In 1900 one second was defined as being 1/86,400 of a mean solar day and stayed that way until 1960 when it was redefined as some fraction of the time it took the earth to move around the sun in 1900, it wasn't until 1967 that the modern definition was used. From 1790 to 1960 one meter was defined as being one ten millionth of the distance between the north pole and the equator, in 1960 it was redefined as being 1,650,763.73 wavelengths of a particular emission line of Krypton-86 in a vacuum, and then redefined to it's modern value in 1983.

    The redefinition of the second in 1967 and the meter in 1960 in terms of the behaviour of light came about because of the recognition of the constancy of its behaviour in a local reference frame.
     
  10. przyk squishy Valued Senior Member

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    Theoretical simplicity is not and never has been a stated priority in physics. Correctness is. Your "simple" explanation is an oversimplification of general relativity to the point of actual fallacy.


    That statement implicitly presupposes a global concept of simultaneity or synchronicity. There isn't one in general relativity. Simultaneity (and therefore comparisons between spatially separated clocks) is already reference-frame-dependent in special relativity. This is why Einstein devotes an entire subsection of his 1905 paper on defining and discussing the meaning of simultaneity in special relativity. It isn't trivial. If you ignore that, you will not understand relativity.


    Since neither you nor I would be in free fall in that case, you've evaded the point I was making: gravitational time dilation largely disappears in free-fall frames.


    Relative to whom? According to what measure of time dilation? Are you staying outside the black hole or following just behind me?

    If you insist that I'd be "time dilated" and that I'd just "freeze on the horizon" and it's just that simple and the questions I just asked above don't matter, then please do one of the following:

    1. Explain, in full, how that prediction is derived from the theory. Prove that the result is really a physical one and not just an artefact of coordinate definitions or just some particular observer's point of view.
    2. Alternatively, cite the experiment, performed in the vicinity of a black hole event horizon, that demonstrated this.


    How would you know? You've never subjected your understanding to any sort of test. You log onto this forum and post stories and quote things other scientists said. But you never do your own analysis. You never derive anything yourself. You never check that your understanding is able to get you to the right results. It's easy to believe just about anything you want if you don't do that. The internet is already full of sad case examples.

    By contrast, I know I've got a substantial level of understanding of general relativity because I can test myself on that. If you put me on a desert island with only pen and paper, I could do the following in maybe a day or so:
    1. Rederive the basic formulation of general relativity, including the principle of general covariance and the geodesic equation, more-or-less as given in Einstein's 1916 paper.
    2. Prove that the weak field metric is an approximate solution to the Einstein field equation that approximately recovers Newton's theory of gravity.
    3. Derive GRs prediction of gravitational time dilation that you like to talk about so much.
    4. Prove that the Schwarzschild metric is an exact vacuum solution to the Einstein field equation.
    With more time and enough motivation, I might just be able to derive the Mercury perihelion advance and gravitational lensing. (These would be more difficult because I've never specifically studied how to do these. I'd really be on my own there. I could at least formulate the problem, though, even if I got stuck doing the actual calculation.)

    And I just claim a basic understanding of the theory. Enough that, if I got a job working on some GR experiment like Gravity Probe B, I could do it after a reasonable adjustment period. A real expert, with research level experience in general relativity, would easily be able to do all of this and a lot more besides.
     
    Last edited: Mar 11, 2014
  11. przyk squishy Valued Senior Member

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    I suggest you do some historical research, Farsight. In particular:

    1. When did experiments start measuring the speed of light? When did experiments start finding that the speed of light was invariant?
    2. When was the invariance of the speed of light first proposed as a physical postulate? When was relativity first proposed as a theory?
    3. When was the current definition of the metre adopted? How were the metre and second defined before that? How were they defined during the historical periods that you identified for questions 1 and 2?
     
  12. Farsight

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    3,492
    No it isn't. The history of the metre doesn't change the current definition. The constancy of its behaviour in a local reference frame is a tautology. Have a look on arXiv and take a look at http://arxiv.org/abs/0705.4507 where Magueijo and Moffat say this:

    "The unit of time is defined by an oscillating system or the frequency of an atomic transition, and the unit of space is defined in terms of the distance travelled by light in the unit of time. We therefore have a situation akin to saying that the speed of light is “one light-year per year”, i.e. its constancy has become a tautology or a definition".
     
  13. Farsight

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    There is no fallacy in what I've said. You're clutching at straws and spitting feathers because I can explain it and you can't, and Einstein and the evidence are with me.

    Yes we know all about that thanks. And still the lower clock goes slower. Gravitational time dilation happens.

    No I haven't. Because I let go. And then...

    ...you start ducking and diving, trying to save face.

    Because like I said, Einstein and the evidence are with me, and I can explain it.

    But you don't understand it, you aren't in line with Einstein and the evidence, and you can't explain anything. You've been taught parlour tricks, that's all. Now pay attention and maybe we can redress some of that.

    We know all this. Now go and read what Einstein said and stop behaving like some catch 'em young Sunday school kid. Start thinking for yourself.
     
  14. Trippy ALEA IACTA EST Staff Member

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    Yes it is, the current definition is irrelevant, it doesn't matter if we use the current definition or the definitions in use when Einstein wrote his papers, the result is the same.
     
  15. Farsight

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    The current definition is relevant. And it's a better definition than the old definitions because it's in line with relativity and pair production and electron diffraction and the wave nature of matter. And as for Einstein and his papers, pay attention to what the guy said:

     
  16. przyk squishy Valued Senior Member

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    Um, what? Oversimplification is a fallacy. Gravitational time dilation is much more subtle than you're giving it credit for.


    You do not understand Einstein. Your references to Einstein are mostly out-of-context quote mines which are not representative of his work. You also still seem to be having a problem with this whole "argument from authority" thing.

    You've also incapable of quantitatively explaining any of the known evidence supporting general relativity.


    Then why aren't you accounting for it?

    I'll grant you that ambiguity with simultaneity is a nit pick if we're just talking about GR effects near the Earth's surface, where relativistic effects generally aren't significant anyway. But if you're going to extrapolate all the way to, say, a black hole event horizon, well you've got no justification for doing that whatsoever.


    No, not always. For example, at least according to the theory, clocks on the ISS should run slightly slower than ours, despite the ISS being at higher altitude than us.

    See, this is exactly the sort of thing you keep leaving out: it's not just how high up the clocks are that matters. It also matters what they're doing. For instance, it makes a difference that the ISS is orbiting the Earth instead of just sitting suspended in the sky. Since this is relativity, things like whose perspective you're talking about also make a difference. And since this is general relativity, it can also matter exactly how comparisons are being made when you start dealing with strong gravitational fields (the gravitational field around the Earth isn't strong by relativistic standards).


    So you were evading my point then.


    No, I challenged you with a specific question and you obviously couldn't answer it. So, you said something that you can't support with either a theoretical derivation or any evidence, and you try to pretend that's my fault?

    I mean, how dare I ask such a pointed question and expect a detailed answer from you? It's like I've mistaken physics for a rigorous precision science or something!


    So you knew that the speed of light was known experimentally to be invariant for a full century before we put it into our SI definitions? In other words, the speed of light is invariant regardless of the SI definitions du jour. You just decided to leave that out then?


    Why don't you "go and read" an actual formulation of general relativity, like the one Einstein himself gave in his 1916 paper? And start thinking for yourself. Physics simply isn't done by stringing together quote mines.
     
  17. Beer w/Straw Transcendental Ignorance! Valued Senior Member

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    It's intimidating how Farsight substitutes Einstein for Jesus.

    Though, don't see him quoting the math.
     
  18. OnlyMe Valued Senior Member

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    Farsight, two of the references Wiki cites, for the parallel mirror light clock hypothetical, actually try to describe how a variation of the hypothetical is constructed, including photocells and both counting and trigger mechanisms.., as if these represent any real clock. Those, at least taken out of context, are misleading, if not worse... And are further proof of my complaint. Too many explantations of what is theoretical, are presented in terms that sound as if the underlying postulates and assumption have been proven, in some universal sense.

    Parallel mirror light clocks remain a hypothetical analogy, based on assumptions about reality that have as yet been unproven.

    My objection has not been the use of the parallel mirror light clock to represent an aspect of SR and GR, it is attempting to use the hypothetical as some kind of proof. The fact that we can imagine something based on good underlying assumptions is not the same as proving it experimentally.

    Are you really trying to suggest that the word frequency has no definition other than as a description of the frequency of light, EM waves and perhaps sound? Even if that is the case, the Cesium clock frequency I referenced, is a microwave frequency associated with electron transitions. To have repeated transitions emitting a microwave frequency, the electron must cycle in both directions between higher and lower energy states... And still we are talking about transitions per second which can be described as transition frequency, even if you set aside the associated microwave emission. Other optical clocks use higher frequency transitions, associated with higher frequency EM spectrum(s), but none of them are measuring the speed of light. And none of them say anything beyond theory, about how other mechanisms would be affected by location in a gravitational field.

    The affect that the location in a gravitational field has on an optical clock, represents a significant step in confirming GR predicted time dilation.., but it does not represent the final word. For time dilation to be "proven" it must be observed in the context of change that is associated with mechanical or chemical rates of change.

    This is not an attempt to say time dilation does not occur, it is just an attempt to, once again.., point out the difference between what remains theoretical and what has been demonstrated experimentally to be a universal truth.
     
  19. Maxila Registered Senior Member

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    They are right, what many people don't realize both speed and time are equally defined as a ratio to distance. Where speed is s, and t is time and x is distance it doesn't matter if you write t=x/s or s=x/t, they are coincident as a magnitude of change relative to distance. When one talks about a frequency being cycles per second, in an empirical event the cycle is a repeating change in length (often a wave length) equal to x making the cycle equal both x/t and x/s, you can't separate the relationship of time and speed to a distance.

    What you get from the definition of a second is a cycle ("the period"), 192,631,770Hz = 9,192,631,770λ (the same thing as distance x) = 1 second, or we could write 9,192,631,770Hz = 9,192,631,770λ/second or 9,192,631,770Hz = 9,192,631,770λ/c. Time and speed are the same relationship to distance it doesn't matter which one is the denominator. The one that best represents the physical relationship for most is, second=9,192,631,770λ/c with c representing the magnitude of change within the distance of 9,192,631,770λ; only because most people don't intuitively see time (a duration) as a magnitude of change withing a distance; however when you examine it empirically, it always is.

    When you understand the meaning of that its rather silly that people think they can separate speed from time as they are coincident ways to state a magnitude of change within a distance as a ratio to distance. Where time and distance have a relative relationship to another observer, a speed like c must too, if it is to remain invariant to time and length in each observers local frame; and yes, I am agreeing with experiments c is observed invariant to time and length for all observers, its just most people don't have a clue what that really means.
     
  20. Farsight

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    No it isn't. Don't try to make it complicated to satisfy some kind of hubristic arrogant sense of superiority.

    I understand Einstein, he said what he said, don't dismiss it as quote-mining argument-from-authority because it doesn't tally with what you've been taught.

    There is no way to quantitatively explain that the speed of light is not constant.

    See the black hole thread for that extrapolation.

    Oh for God's sake przyk, we know all about SR slowdown and GR speedup as per Phil Fraundorf's image.

    No, you're evading mine. Now look at the thread title, look at the Einstein quotes, look at the OP, look at the evidence, and face up to it.

    See above. Don't try to evade Einstein and the evidence by hiding behind mathematics.

    Yes, I know, and yes, I've left a lot out. The OP is around a thousand words. If I made it longer people are less inclined to read it. I also left out why the SR postulate applies, because of the wave nature of matter, see the other meaning of special relativity by Robert Close.

    I have. And may I remind you that you're the one dismissing Einstein, not me.
     
  21. Farsight

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    IMHO most physicists accept relativity, and they accept the parallel-mirror light clock even though it's an idealization. All I've done here is substituted the NIST optical clock for a depiction of parallel-mirror light clocks and reminded you that there's no actual river of time flowing in any clock. You shouldn't have a problem with the idea that a clock clocks up some kind of regular cyclic motion, and if a clock goes slower that motion is going slower.

    Your objection noted. All I can do is present my case and ask you to think it through.

    No. Where did you get that idea?

    No! It isn't the frequency of the hyperfine transitions, it's the frequency of the emitted light. Think of one electron dropping to a lower energy state. That's one event. That one event has no frequency. But emitted light does.

    The point is that when you are defining the second using some light, you cannot say "this light has a frequency of x" because frequency is cycles per second and you haven't defined the second yet.

    Have no doubt that gravitational time dilation is proven.

    General relativity is one of the best-tested theories we've got. See Clifford M Will's paper at http://arxiv.org/abs/gr-qc/0103036 . The issue isn't one of experimental proof, it's one of interpretation.
     
  22. Farsight

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    Well said. I am reminded of the light-year. The Earth moves through space, and a light beam moves through space. We wait until the Earth has gone round the Sun once, then we point to the light beam and say "that distance is a light year". But a year is a time, and you could dispense with the Earth.

    True. IMHO most people don't think about pair production or electron diffraction or the wave nature of matter. We are made of waves. Everything is. Have a look at the other meaning of special relativity by Robert Close.
     
  23. nimbus Registered Senior Member

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    Przyk, your patience is phenomenal.
     

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