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Special Theory of Relativity Incorrect?

  1. Apr 18, 2010 #1
    I do not believe the Special theory of relativity is in correct, however the question did come up in class the other day.

    If some people do believe it to be incorrect, than what are some of these theories as to why it is in correct? I was just wondering and curious about the whole subject. I did infact read somewhere that some scientists have a theory that the speed of light has actually slowed down over billions of years.

    what are some other theories as to why Speical Relativity is incorrect ?
     
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  3. Apr 18, 2010 #2

    Jonathan Scott

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    There is a lot of experimental evidence that Special Relativity is completely accurate at the macroscopic level, at least in situations where no correction for General Relativity is required.

    There is however a well-known clash between Special Relativity and Quantum Mechanics which suggests that Special Relativity is incomplete or inaccurate in some way at the quantum level.

    The theory of entanglement in quantum mechanics (well confirmed by experiment) appears to require faster-than-light communication, although not in a form which could be used to send a signal. If such communication exists in any arbitrary inertial frame of reference then according to Special Relativity that would apparently allow the communication to go backwards in time in some cases, violating causality. To preserve causality, this means that either quantum mechanics requires some preferred frame (violating the principles of Special Relativity) or that some other more exotic departure from the Special Relativity universe is required, as for example in the Many-Worlds Interpretation (MWI).
     
  4. Apr 18, 2010 #3
    Oh wow i didnt know that the two were related, do you possibly have a link to where I can read more about this contradiction ?
     
  5. Apr 18, 2010 #4

    Matterwave

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    Entanglement does not necessarily imply violation of Special relativity. It could also just be that "counter-factual definiteness" (the act of "being" in one state or another) does not exist at the microscopic level. Bell test violations means we need to throw away one of 3 assumptions that EPR made:

    1) Induction (a foundation of science and therefore usually people keep this one)
    2) Locality (no information transfer is possible at speeds greater than c)
    3) Realism or "counter-factual definiteness" (the fact that things are there or are in a certain definite state even when we don't observe them)

    There is no reason to doubt locality above realism imo.
     
  6. Apr 18, 2010 #5

    Dale

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    I agree with Matterwave that enganglement does not imply a violation of SR. The disconnect between QM and SR that Jonathan Scott refers to has been resolved for several decades, and its resolution was a key step in the development of QED which is a relativistic quantum theory. Since there is a relativistic quantum theory which predicts entanglement it is difficult to claim that entanglement violates relativity.
     
  7. Apr 18, 2010 #6
    To my knowlegde there are contradictions between quantum physics and general relativity. What is the nature of thoes?
     
  8. Apr 18, 2010 #7

    Jonathan Scott

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    I think you're mixing up things here. Relativistic quantum theory (which started with the Dirac equation and is perfectly consistent with SR) is not specifically related to entanglement, which is a separate issue that was only spotted much later, as in the Einstein-Podolsky-Rosen (EPR) paradox and later in the Bell inequalities.

    As Matterwave mentioned the explanation of entanglement doesn't necessarily contradict the basic principles of SR, in that it is possible to assume instead that some other fundamental assumption in physics is violated instead. However, one way or another, the world of QM is not compatible with the world normally assumed in SR.
     
    Last edited: Apr 18, 2010
  9. Apr 18, 2010 #8

    Jonathan Scott

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    In quantum theory, forces are mediated by particles which transfer momentum and energy between objects and fields. In General Relativity, gravitational forces are transmitted by the curvature of space, and empty space does not contain any momentum and energy, at least from the point of view of a frame which is in free fall. These viewpoints are incompatible.

    It may be that this is primarily a problem with the viewpoint, and that the underlying physics is actually compatible, at least to a high degree of accuracy, but attempts to find different viewpoints that are consistent with both GR and QM have not been successful.
     
  10. Apr 18, 2010 #9
    Dirac equation-based quantum mechanics admits entangled states to exactly the same degree as Schroedinger equation-based quantum mechanics, since they both take the form of operator equations on states living in a complex Hilbert space. Entangled states are just a manifestation of the existence of superposition states in a multi-particle Hilbert space.
     
  11. Apr 18, 2010 #10
    This is not really a coherent idea. The speed of light is a dimensionful quantity, meaning that it can only be measured relative to certain standards of measurement for distance and time. If we were to measure the speed of light at two different times and find it to be different, it would be, at the level of fundamental principles, impossible to tell whether it was the speed of light that had changed or whether it was our standards of measurement.

    If we want to talk about the possibility of physical constants varying, the best we can do is ask whether dimensionless constants (like the fine structure constant or the ratio of the electron and proton masses) have changed over time.
     
  12. Apr 20, 2010 #11
    At least one of the propositions that the speed of light may have changed is made on the basis that vacuum permittivity and permeability had changed over time (if I remember correctly) The author may have alternatively referred to electric susceptibility which can be broken down into permittivity.

    Permittivity has dimensions Farads/meter. So the length dimension could remain invariant.

    PS. Kind of sounds like space is just one big capacitor. (Just kidding)
     
    Last edited: Apr 20, 2010
  13. Apr 20, 2010 #12
    A few comments. First, if it somehow were the case that the speed of light had changed it would automatically follow that at least one of [itex]\epsilon_0[/itex] and [itex]\mu_0[/itex] had changed, since [itex]c=\frac{1}{\sqrt{\epsilon_0\mu_0}}[/itex].

    Second, it doesn't matter what dimensionful constant we're talking about. It's still impossible to tell the difference between the constant having changed and the physics underlying our measurement standards for the dimensions of that constant having changed. That said, if the permittivity and/or permeability of free space had changed in a way that the speed of light changed as well, at least one of the length and time dimensions would, of necessity, have to be involved.
     
  14. Apr 20, 2010 #13

    Dale

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    I agree 100% with Parlyne here. The dimensionful universal constants tell us about our system of units, not about physics. It is only dimensionless fundamental constants that really describe physics.
     
  15. Apr 21, 2010 #14
    There is some empirical evidence that the Special Theory of Relativity is wrong.
    http://calgary.rasc.ca/algol_minima.htm

    You will notice that light from Algol passes us more quickly when we are approaching and passes us more slowly when we are receding.
    Of course, we are in the same situation we were back in 1500 when everybody 'knew' that the Earth was stationary. Now in 2010, everybody 'knows' that the speed of light is constant relative to all observers. Hopefully it won't take us hundreds of years to realize we are wrong.
     
    Last edited: Apr 21, 2010
  16. Apr 21, 2010 #15
    I see your point(s) and suppose that any such argument that the speed of light has changed would have to be convincing both within SR and from a classical perspective. Seeing that dimensionless constants like the fine structure constant are composed of subcomponents (vacuum permittivity for example) in such a way that the dimensions all cancel, they're not able to be directly measured. So if someone was interested in investigating this further they would probably need to look for measurements or combinations of measurements where time and length drop out leaving some other dimension remaining.
     
    Last edited: Apr 21, 2010
  17. Apr 21, 2010 #16

    Jonathan Scott

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    You're confused; the description is perfectly consistent with Special Relativity. The information in the light about the minima is more bunched up when we are moving towards it than away, so the rate at which changes occur is modified, but the speed at which the light arrives is still c.
     
  18. Apr 21, 2010 #17

    Dale

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  19. Apr 21, 2010 #18
    Do you care to elaborate? Can you explain why this doesn't imply that the light is passing us more quickly when we are moving towards Algol and more slowly when we are moving away? If I have people in a line that are running towards me at a constant speed and they're equally spaced apart and I then start running towards them in the opposite direction that they're moving, both their speed relative to me will increase and there will be a decrease in time from person to person. This seems pretty simple to understand. So can you explain why this analogy doesn't hold?
     
    Last edited: Apr 21, 2010
  20. Apr 21, 2010 #19
    Well I'm no expert at GR, but as far as my knowledge of Modifications of Sr goes, it works completely fine at macroscopic distances and small energy levels.

    The error comes from the fact that by Principle of Relativity, not only is c constant in all inertial frames, but all physical constants are. And since h (Planck's const) is same for all too, there is a limit on energy density possible, given by Planck unit for Energy Density, same as that for Pressure.

    Hence at very small distances, and ultra-relativistic domains, even without GR, there is a correction in SR.
     
  21. Apr 21, 2010 #20
    Think of it in this way. If people are being emitted at a constant rate from a point that moves towards you at c/2 and they start running towards you at speed c relative to you, it's clear that the rate at which they collide with you will be higher than the rate at which they are being emitted.
     
  22. Apr 21, 2010 #21
    Do you believe that the Einstein equivalence principle (EEP) is correct? (It has been tested to very high
    precision.) The EEP says that the results of all local non-gravitational test experiments are independent of
    where and when they are performed. Since the physics underlying modern measurement standards is
    just local non-gravitational physics, it follows that the description of gravitational physics does not depend
    crucially on the choice of units as long as the EEP holds.

    This means that, it is perfectly reasonable to speak of a change of the gravitational "constant" G as long
    as the local non-gravitational physics is unchanged. In fact, the alternative of referring to a change of
    dimensionless constants including G, while basically correct, can be misleading, since it implicitly
    assumes that the EEP does not necessarily hold, making things unnecessarily complicated. So, your
    comment on units is of course correct in the context it was made, but it cannot be used as a general principle.
     
    Last edited: Apr 21, 2010
  23. Apr 21, 2010 #22

    JesseM

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    From a post on another thread, here's an example I made up to show how you can derive the relativistic Doppler effect using the assumption that the signals are still moving at c:

    The Doppler effect is just a consequence of the fact that if an object emitting regular signals (or peaks of a continuous wave) is in motion relative to you, then each signal (or peak) has a different distance to travel to reach your eyes...the relativistic Doppler effect also factors in time dilation, but that's the only difference. For example, suppose a clock is traveling away from me at 0.6c, and it's programmed to send out a flash every 20 seconds in its own rest frame. In my frame, because of time dilation the clock is slowed down by a factor of [tex]1/\sqrt{1 - 0.6^2}[/tex] = 1.25, so it only flashes every 1.25*20 = 25 seconds in my frame. But that doesn't mean I see the flashes every 25 seconds, the gap between my seeing flashes is longer since each flash happens at a greater distance. For example, suppose one flash is emitted when the clock is at a distance of 10 light-seconds from me, at time t=50 seconds in my frame. Because we assume the light travels at c in my frame, if the flash happens 10 light-seconds away the flash will take 10 seconds to reach me, arriving at my eyes at t=60 seconds. Then, 25 seconds after t=50, at t=75, the clock emits another flash. But since it was moving away from me at 0.6c that whole time, it's increased its distance from me by 0.6*25 = 15 light-seconds from the distance it was at the first flash (10 light-seconds away), so it's now at a distance of 10 + 15 = 25 light-seconds from me, so again assuming the light travels at c in my frame, the light will take 25 seconds to travel from the clock to my eyes, and since this second flash happens at t=75 in my frame, that means I'll see it at t=100 seconds. So, to sum up, the clock flashes every 20 seconds in its own rest frame, and once every 25 seconds in my frame due to time dilation, but I see the first flash at t=60 seconds and the second at t=100 seconds, a separation of 40 seconds. This means the frequency that I see the flashes (1 every 40 seconds) is half that of the frequency the clock emits flashes in its own frame (1 every 20 seconds), which is exactly what you predict from the relativistic Doppler equation if you plug in v=-0.6c (negative because the clock is moving away from me): [tex]\sqrt{\frac{1 - 0.6^2}{1 + 0.6^2}} = \sqrt{0.25} = 0.5[/tex]. And you can see from the italics above that I specifically assumed the light from each flash traveled at exactly c between the clock and my eyes.
     
  24. Apr 21, 2010 #23

    Dale

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    The analogy does not hold because the speed of people running is not frame invariant, the speed of light is.

    The first-order Doppler shift is not an evidence either for or against relativity. Doppler shifts happen in both Newtonian physics and Special Relativity, in addition, Doppler shifts happen both for waves like light whose speed is frame invariant and waves like sound whose speed is not frame invariant. So the mere first-order observation of Doppler shift doesn't tell you much about the possible laws governing your wave.

    However, the relativistic Doppler shift and the Newtonian Doppler shift differ in their second order terms and geometrically in the so-called "transverse Doppler shift". These have been measured experimentally to very high precision and are in agreement with the SR predictions to within 2 parts per million.
     
    Last edited: Apr 21, 2010
  25. Apr 21, 2010 #24
    Yes, see here
     
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