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Today Special Relativity dies

  1. Jun 20, 2004 #1
    Mark it on your calendars, people. Let us begin.
    Case #1:
    Code (Text):

    [u]|(->                    (o)                    <-)|[/u]
     
    man standing on a movable platform bed. at the EXACT center between two photon emitters. SR concludes that the simultaneously emitted photons from the two emitters will be detected by the observer at the same exact time.

    ADDENDUM:the photon emitters are tied to precise atomic clocks

    these clocks are perfectly aligned and synchronized and in all cases they move within the same inertial frame so they can stay calibrated.

    (True / False) ?

    Case #2:
    Code (Text):

    [u]|(->                    (o)                    <-)|[/u]
       [u]|(->                    (o)                    <-)|[/u]
          [u]|(->                    (o)                    <-)|[/u]
             [u]|(->                    (o)                    <-)|[/u]
     
    Platform is moving. SR concludes the photons (still emitted simultaneously) will be detected by the observer at the exact same time.

    (True / False) ?

    Case #3:
    Code (Text):

    [u]|(->                    (o)                 <-)|[/u]
    [u]|(->                       (o)              <-)|[/u]
    [u]|(->                          (o)           <-)|[/u]
    [u]|(->                             (o)        <-)|[/u]
     
    Man is moving on platform towards an emitter. SR concludes that photons are NOT detected at the exact same time.

    (True / False) ?

    once we square these we'll move on to stage 2.
     
    Last edited: Jun 20, 2004
  2. jcsd
  3. Jun 20, 2004 #2
    Simultaneously, but simultaneously in which frame? You cant' omit that.

    Case #1 there is only frame, so assuming simultaneously in that frame, true.

    Case #2 there is one frame (not counting the background), so assuming simultaneously in that one frame, true.

    Case #3, there are two frames (man and emitters). So in which frame are the photons emitted simultaneously? If man frame, false (detected at the same time). If emitter frame, true (not detected at the same time).

    That's my answer according to my understanding of SR.
     
  4. Jun 20, 2004 #3

    Chronos

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    huh? if both frames are moving relative to each other, they must obey SR to measure one to the other. what is so difficult about that? it has been proven in particle accelerators many times.
     
  5. Jun 20, 2004 #4

    jcsd

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    In all cases we have 2 refrence frames.

    In case 1 these are the same so in both reference frames the phtons are emitted and detectd simultaneously

    In case 2 these refrnce frames are different, in our reference frame i.e. the 'stationary' frame we conclude the phtons are emitted and detected simulatenously. In the refrence frame of the man THIS IS NOT THE CASE; the man does not think the phtons are emitted simultaneously, but he does conclude that they are detected simultaneously.

    In case 3 in our refernce frame we conclude that the phtons are emitted but not detected simulatenously. In the refernce frame of the man, the photons are not emitted simulataneously and they are not detected simulataneously.
     
  6. Jun 20, 2004 #5

    russ_watters

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    We've had this discussion before: you can't prove/disprove a theory with a thought experiment, only with evidence.
     
  7. Jun 20, 2004 #6
    For Case#2 I didn't consider the stationary background frame in my reply. If the photons are emitted simultaneously in the stationary background frame, the photons are not emitted simultaneously in the moving platform frame, therefore the man does NOT detect them at the same time. There I disagree with jcsd.

    ram, will you please specify the frames in which the photons are emitted simultaneously? Is it the stationary background frame in all cases? You can't expect too many replies for a poorly specified scenario.
     
  8. Jun 20, 2004 #7

    jcsd

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    There is ceratinly plenty of ambiguity as ram failed to define reference frames, I just assumed that ram's drawings refer to the point of view of the 'stationary frame' and hence it is in this frame that the photons are always emitted simulatenously.

    However you are incorrect still as simulatenity fails only at distance, so if the photons are detected simulataneously in one frame, they're detected simulatenously in all frames.

    edited for about 100 typos
     
    Last edited: Jun 20, 2004
  9. Jun 20, 2004 #8
    Yes I know simultaneity fails only at distance. And, the photons cannot be detected at the same time by the man [for case#2, if photons are emitted simultaneously in background frame] They would be detected at the same time by a midpoint observer in the stationary frame. But the man does not remain at that midpoint, so he does not detect them at the same time.
     
  10. Jun 20, 2004 #9

    Janus

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    Just to add my voice to what has already been said. You must state which frame the lights emit simultaneously in. Is it according to us, the background observer or is it according to the emitters themselves.

    In the first case, they are one in the same.
    In the second case they aren't
    In the third case they are the same again.

    Also, in the third case, it depends on where the man is on the platform when he detects the photons. If he is exactly between the two emitters when he does, he will detect the photons simultaneously. But this doe not mean that the photons were emitted at the same time in his frame (in fact, from his frame, they can't have been emitted simultaneously.) That is the whole point of Relativity of Simultaneity, that distance separated events that are simultaneous in one frame are not simultaneous in a frame moving relative to the first.

    It is a consequence of the invarience of the speed of light for all observers.

    And as also already pointed out, you can not kill a theory with a thought experiment. All a thought experiment can do is show you the consequences of any given postulates. It takes a physical experiment to show whether or not the results of the thought experiment agree with reality or not. So far, every physical experiment designed to test the predictions of Relativity has supported the conclusions of Relativity.
     
  11. Jun 20, 2004 #10

    Hurkyl

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    (NOTE: This was in response to the original posting)

    In all cases, I will assume by "simultaneously emitted photons" you mean that emission was simultaneous in the frame in which the picture is drawn.


    Case #1: True.
    Case #2: False.
    Case #3: True.

    Since there is some disagreement in case #2, so I'll explain my answers.



    disagreement with wespe:
    Given the presentation of the problem, I'm assuming that "simultaneous" means that they're simultaneous according to the "background". However, you are correct if we assume that ram2048 means that emission was simultaneous in the frame of the platform.

    disagreement with jcsd:
    In our frame, the guy is at the midpoint of the emitters when they flash, but he's moving towards the right emitter; thus he has to detect the right photon first. In the moving frame, they are indeed not emitted simultaneously, but the guy will still detect the right photon first.
     
    Last edited: Jun 20, 2004
  12. Jun 20, 2004 #11

    jcsd

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    Yep, sorry you're correct. I what I incorrecty did was take the refernce frame of the platform which is the same as the staionary frame in the other two case.
     
    Last edited: Jun 20, 2004
  13. Jun 20, 2004 #12
    Hurkyl, by "Case #3: False.", do you mean "detected at the same time" or "not detected at the same time"?

    Ram, look at the mess you put us in. Clean this up! LOL
     
  14. Jun 20, 2004 #13

    Hurkyl

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    Good catch; it's been fixed.
     
  15. Jun 20, 2004 #14
    the clocks in all cases emit photon simultaneously RELATIVE TO EACH OTHER.

    these clocks are perfectly aligned and synchronized and in all cases they move within the same inertial frame so they can stay calibrated.
     
  16. Jun 20, 2004 #15
    Do you realize you wasted people's time by not specifying this in the first place? OK, in that case, #1 and #2 are true.

    But, as Janus says, #3 is still unclear: where is the man when he detects the photons?
     
  17. Jun 20, 2004 #16
    does it matter where the man is?

    he's obviously NOT in the center...

    you can put real values to it if you like and work it out from there. however you want to make it easier for you.

    and as far as wasting people's time, we've got ALL DAY, you in a hurry? :D
     
  18. Jun 20, 2004 #17
    Then, he does not detect them at the same time. #3: true


    I might have better things to do if you'll excuse me

    Take care.
     
  19. Jun 20, 2004 #18
    so do we have (True, True, True) yet?

    need couple more opinions/verifications then we can move to the next stage
     
  20. Jun 20, 2004 #19
    editting main post to include the clock bit, since it confuses you guys. I thought it was self explanatory, my bad.
     
  21. Jun 20, 2004 #20

    jcsd

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    You need to define which refernce frame the [phtons are emitted simultaneously, the stationery observer's, the platform's or the man's.

    edited to add so the clocks are in the rest frame of the platform?
     
    Last edited: Jun 20, 2004
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