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What exactly is the solution for principle of locality and speed of light?

  1. Sep 2, 2009 #1
    how do physicists solve this contradiction (when information moves faster then the speed of light)?
    thanks
     
  2. jcsd
  3. Sep 2, 2009 #2

    f95toli

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    There is no contradiction because information never travels faster than the speed of light.
    Although I am not sure what you are refering to by "principle of locality"?

    Note that entaglement etc can NEVER be used to transfer information FTL, no one has ever identified a situation where QM contradicts SR.
     
  4. Sep 2, 2009 #3

    zonde

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    I would say that at the present state of things there are several alternative solutions for this contradiction but none of them says that information moves faster then the speed of light.
    Good thing is that all the alternatives relay on the same mathematical formalism. So we can expect that there will be some job for Occam's razor in the future.
     
  5. Sep 2, 2009 #4
    so how one particle affect other at the time? (if it does)
     
  6. Sep 2, 2009 #5

    zonde

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    Obviously they don't as that would involve FTL interaction.
    But we can speak how measurements affect each other as they are communicated no faster than light speed.
     
  7. Sep 2, 2009 #6
    Günter Nimtz...


    A controversial exception has already been identified, Günter Nimtz, a German physicist has already demonstrated that photon particles carrying information can travel at superluminal velocities while quantum tunneling via virtual photons.

    1994 Nimtz and Horst Aichmann shown an experiment at the laboratories of Hewlett-Packard using microwaves through a straitened passage of a waveguide. Nimtz says that the Frequency modulated (FM) signals transports the 40th symphony of Wolfgang Amadeus Mozart 4.7 times faster than light due to the effect of quantum tunneling.

    This experiment is video demonstrated in reference 2, the differential signals arrive on an oscilloscope detector that demonstrates the tunneling photon signals arrive faster than vacuum photon signals, also while carrying information, however the received information is attenuated.

    I have also corresponded with a professor at the University of Cologne that has studied Nimtz scientific papers and concluded that the superluminal quantum tunneling effect is also possible with particles with mass.

    Although theoretical, I have never seen an experiment that demonstrated a superluminal quantum tunneling virtual mass particle.

    Reference:
    http://en.wikipedia.org/wiki/G%C3%BCnter_Nimtz" [Broken]
    http://www.youtube.com/watch?v=UI7nPmlgBEk"
    http://en.wikipedia.org/wiki/Quantum_tunnelling" [Broken]
     
    Last edited by a moderator: May 4, 2017
  8. Sep 2, 2009 #7
    Criticism sound not very convincing at wavelength was 33mm and gap was 1 meter wide, while GPS in my smartphone have a precision of 5 meters measuring the ‘arrival times’ of the satellite signals. I believe such intervals can be measured very accurately.
     
  9. Sep 2, 2009 #8

    Cthugha

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    Re: Günter Nimtz...

    Not that crap again. This has been discussed in these forums several dozen times and it is pretty clear that the tunneling photon do NOT travel faster than c. Nimtz uses the speed of the pulse peak for measuring signal propagation, which is nonsense, especially if the shape of the pulse changes like in Nimtz' experiments. The speed of the peak is not the speed at which information is transmitted and it is also not the speed of particles.

    This is like trying to measure the speed of a moving train and taking the position of the passengers as the measure of the speed of the train. If all of the passengers move from the back to the front of the train you will measure a faster train according to your definition although the speed of the train is constant all the time.
     
  10. Sep 2, 2009 #9
    What if there is only one peak (delta function)? Only one very short pulse?
     
  11. Sep 2, 2009 #10

    Cthugha

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    Nimtz' experiments rely on the fact that his tunnel barriers cause nonlinear pulse damping. The "front part" of the wave is less damped and the "back part" gets damped heavily. If you just have a delta peak, you will only see a damped peak coming out without any shift in time. He uses just a clever version of pulse shaping using anomalous dispersion.
     
  12. Sep 2, 2009 #11

    Although reshaping does occur especially for quantum tunneling multi-photons, it does not account for superluminal quantum tunneling single-photons.

    I also refuse to accept the argument that Stanford University and AT&T Bell Laboratories professors that are aware of the reshaping effect are incapable of measuring the velocity of quantum tunneling photons.

    Reference:
    http://www.dhushara.com/book/quantcos/qnonloc/qnonloc.htm" [Broken]
     
    Last edited by a moderator: May 4, 2017
  13. Sep 2, 2009 #12

    Cthugha

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    A reference constantly misspelling Paul Kwiat as Paul Kwait is pretty suspect. Fortunately there are the original publications of the authors to check, what they really intended to say. Check for example:

    A. M. Steinberg, P. G. Kwiat, and R. Y. Chiao
    Measurement of the single-photon tunneling time
    Phys. Rev. Lett. 71, 708 - 711 (1993)

    Where they conclude:
    "Our measurements indicate that the peak of the undistorted (but attenuated) single-photon wave packet appears on the far side of a tunnel barrier earlier than it would were it to propagate at c. There is, however, no genuine violation of Einstein causality, as explained above."

    As explained in the paper this is a result of postselection combined with low probabilities. You only select the transmitted photons and the transmission probability is indeed low. See references 22 and 23 in the paper I quoted for further discussion on that topic.

    So in conclusion: The authors do not draw the conclusion you would like them to draw. There is no information transfer at superluminal velocities according to the authors you mentioned.
     
    Last edited by a moderator: May 4, 2017
  14. Sep 2, 2009 #13

    If the tunneling photon (virtual photon) is not a genuine signal then virtual photons could not relay quantum information and also frequency modulated photons could not traverse the barrier, that is the photons that leave the barrier would still be attenuated but not frequency modulated.

    If the tunneling photon (virtual photon) is not a genuine signal, then polarized photons (quantum information) that enters the barrier would leave the barrier as non-polarized photons.

    The tunneling velocity is too high for 'pulse reshaping' because the wave packet distribution for photons are extremely small and this would violate the Heisenberg Uncertainty Principle.

    The paper claims that the tunneling time differential is due to 'pulse reshaping', however it does not state a theorem that proves it.

    Reference:
    "www.ino.it/~azavatta/References/PRL71p708.pdf"[/URL]
    [PLAIN]http://en.wikipedia.org/wiki/Uncertainty_principle" [Broken]
    http://en.wikipedia.org/wiki/Pulse_shaping" [Broken]
     
    Last edited by a moderator: May 4, 2017
  15. Sep 2, 2009 #14

    Cthugha

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    You are completely misinterpreting the paper.

    The paper does not say that the tunneling photons are not genuine signals. It says that the tunneling times are not the times, which it takes to transmit information.

    As you can see in the HOM-dip in figure 3 of the quoted paper the wave packets are indeed pretty broad and long compared to the time difference of 1.47 fs between free space propagation and barrier propagation. Pulse reshaping does not violate the HUP in this case.

    The paper does not even claim that directly. It claims that pulse reshaping is the cause of the tunneling time differential in classical optics and says that the mechanism is a bit different for single photons. However, the mechanism in this case is in fact pretty similar. As you see in figure 3 there is still significant destructive interference for time delays as large as +/- 40 fs showing the underlying detection probability density is of the same width as well. It does really not surprise me that the time dependence of the photon detection probability density is "shaped" in the same way a classical pulse will be shaped. If the peak shift was larger than the HOM-dip this would be a good indication for FTL-information transfer. In this case, it is not.
     
  16. Sep 2, 2009 #15
    people, concentrate, i was talking about EPR paradox, is there a solution?
     
  17. Sep 2, 2009 #16
    Is there a problem? :)
     
  18. Sep 2, 2009 #17

    f95toli

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    As Dmitry67 has already: Is thera a problem?
    It is important to remember that what Einstein and co ASSUMED was a paradox in QM is actually not.
    The starting point of their argument is basically that a certain type of experiments will "obviously" yield a result X (because information can not travel FTL); i.e. they ASSUMED a certain outcome.
    However, when people actually started doing these experiments many years alter this was NOT what was seen meaning the whole line of reasoning leading up to the paradox is actually incorrect.

    And yes; I am simplifying this quite a bit here (both the physics and the history) but the main point is that there IS no paradox; QM is consistent (at least mathematically; that many people enjoy spending ages discussing various intepretations related to the EPR is another story.


    Also, I would like to stress that I am in no way trying to say that the EPR paper was not important because it was -it stimulated an enourmous amount of important work- but that does not change the fact that what they were trying to show in the paper (that QM was inconsistent) turned out to be incorrect.
     
  19. Sep 2, 2009 #18

    DrChinese

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    To add to the above, with which I agree entirely:

    The QM answer is: "This makes the reality of P[position] and Q[momentum] depend upon the process of measurement carried out on the first system..." These words are from the EPR paper itself, although they rejected this idea because they thought it was not a "reasonable definition of reality".
     
  20. Sep 3, 2009 #19

    zonde

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    Somehow solve, one way or another ;)
    ... without any information moving faster then the speed of light.
    If you want solution for you I can recommend deterministic viewpoint involving hidden variables. You can imagine that hidden variables does not hold (yet) any known physical meaning - it is just sophisticated way of numbering particles :)
    With that view in mind you should draw some analogy between wave function collapse and discarding of some particles (subsampling). That way you pick the part of sample that show required correlations in postselection process that does not require any faster than light information transfer.
    There might arise small problem if you afterwards will consider Malus' law. That's because implied explanation for Malus' law is that photons have hidden variable of polarization.
    So it turns out that this way EPR experiments conflict with intuitive understanding of Malus' law.
    However this can be solved if you assume that polarization is not hidden variable of single photon but rather property of sample of photons e.g. their configuration relative to one another plus certain strange arrangement between polarizers that might not seem so strange if you like Bomian interpretation of QM or even have heard about The Invariant Set Postulate hypothesis.
     
  21. Sep 3, 2009 #20

    zonde

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    Thought that I might add this link as it seems relevant to what I said about Malus' law (not completely sure however)
    http://www.springerlink.com/content/0136072643546224/"
    It's Hnilo et al "Low Dimension Dynamics in the EPRB Experiment with Random Variable Analyzers"
     
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