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I Travelling (at) the speed of light away from a lightsource

  1. Feb 26, 2016 #1
    Hi all,
    I was trying to figure out the following:
    Say I am standing right in front of a movie playing on a screen. Then, at time t0, I immediately am traveling at the speed of light away from this non-moving screen. Say I looked back while traveling away. Would I see an image (the frame the screen was showing at t0), or would I see a movie, because the speed of light is constant in all frames?

    Also, to those who alter the question to "you can't travel at c, now say you were traveling at .99c...", then assume I'm massless, and have working massless eyes, and am traveling at c
     
  2. jcsd
  3. Feb 26, 2016 #2

    Orodruin

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    You cannot get around physics by wishing and assuming that it worked differently. You either want an answer to a well defined question within the current working theory or you want a fairy tale.
     
  4. Feb 26, 2016 #3
    Asking what would happen in circumstances that are not physically possible is a bit of a risk, but I'll have a go at it.
    You propose travelling away from the screen at the same velocity as photons are travelling away from it.
    Thus if you had any way to observe the photons (which you won't) you would see a still frame picture of what was on the screen at the time of your departure
     
  5. Feb 26, 2016 #4

    DrGreg

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    This is an example of proof by contradiction (reductio ad absurdum).

    Assumption: there is such a thing as a massless eye moving at ##c##.

    Conclusion: As seen by the eye, the movie would be frozen and the movie would not be frozen.

    The conclusion cannot be true; it contradicts itself. Therefore the assumption must be false.
     
  6. Feb 26, 2016 #5
    I guess what I was trying to get at was: would the result of it being a movie/picture be affected by the fact that the speed of light is constant in all frames? Say that there is no eye. There is just light from the screen traveling through space. From a reference frame moving at speed of light c away from the screen, is it a movie, because c is constant, or is it a picture, because the frame is traveling at the same speed as the light leaving the frame?
    I know it's non-physical, but I asked this question because I want to better understand the implications that c is constant in all frames.
     
  7. Feb 26, 2016 #6

    PAllen

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  8. Feb 27, 2016 #7

    Orodruin

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    If you know it is non-physical, why do you ask the question in a physics forum? There is no reference frame moving at the speed of light! In fact, no reference frame can be said to have a particular velocity unless it is in relation to another reference frame.

    With PAllen's post, I am going to close this thread as it is not going any further.
     
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