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Time dilation video feed experiment

  1. May 14, 2013 #1
    Time dilation
    As I've understood; two parties can experience time, or timespace, differently depending on each parties'
    • velocity
    • gravity

    A debate led to this question:
    ship A and ship B install livecams, each viewing both ships' livefeed on 2 screens*. Ship B launches away from earth** 10^5 times the speed of light with constant speed for 60 seconds. Ship A stays still the whole time.
    How do each party perceive each others feeds?

    * leave out the variable of streaming connection of cameras, presume perfect transmission in terms of latency.
    ** disregard gravitational variables from other planets than Earth.

    NB: I don't study physics, I've seen the rules on homework q's but I didn't know where else to post a difficult q on special relativity.
  2. jcsd
  3. May 14, 2013 #2


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    You have posited a totally impossible situation. Nothing travels faster than light and nothing with mass travels as fast as light
  4. May 14, 2013 #3
    Point taken, thanks. Yet, my interest lies in the perception of the video feeds - is it impossible to presume mass traveling that fast (I don't care about current technology, will it f¤% up the formula, maybe?)
  5. May 14, 2013 #4


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    Which part of my previous post did you not understand? Yes it is meaningless to make that assumption.
  6. May 14, 2013 #5


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    It's not that it messes up the formula, it is that it is physically impossible, for reasons that have nothing to do with current technology - like asking "Suppose I draw a circle of radius R, but I use a special magic pen to draw the circle, and the way the magic pen works, the circumference of the circle isn't 2∏R, it's something larger than that. Now what would I see if used this magic pen to draw a square?" You're not going to get an answer.

    Nor can you ignore the the latency for the signal to travel from one ship's camera to the other's display, and vice versa - because nothing can travel faster than light (if you've heard of "Tachyons" or "Alcubierre" PLEASE PLEASE don't mention them now - learn to walk before you run) there will be a delay, and it has to be allowed for.

    However, there is a similar thought experiment that can be done. One ship stays at rest while the other jets off at .99c (very close to, but not exceeding, the speed of light). The video signals moving between them are transmitted at the speed of light. Both ships will see the exact same thing:

    1) They will see themselves at rest while the other ship is moving away at .99c
    2) The time on their clock will be greater than the time they see in the video image of the other clock (which, of course, left the other ship a while back).
    3) The time difference in #2 will be greater than can be explained just by allowing for the light travel time between the two ships.
  7. May 15, 2013 #6
    I see, thanks. I read some about Tachyons and Alcubierre. Those models are a bit ahead of me, yes:)
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