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Fun food for thought

  1. Dec 8, 2011 #1
    You send a probe out into space at half light speed transmitting continuous video footage. What does the footage look like as seen on earth?
  2. jcsd
  3. Dec 8, 2011 #2

    Simon Bridge

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    It looks like video footage.
    :) Welcome to PF

    The Earth observers would see the carrier wave doppler-shifted.
    If the footage was time-stamped, you'd see evidence for time dilation.
    Was there something specific you were wondering about?
  4. Dec 8, 2011 #3


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    Am I correct in assuming you would have to account for the doppler shift to even understand the signal?
  5. Dec 8, 2011 #4

    Simon Bridge

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    Depend on how the data was encoded.

    If it was an old-style am signal, and it was just audio (say, the pilot reporting her position and time) then you'd just tune your radio receiver in to whatever gets a strong signal and you'll hear her voice a bit on the deep side talking a bit slow. How big-a difference is 0.5c going to make?

    If it was a modern wireless broadband video stream, I don't know the standard. I know it has to be able to handle streaming between different speed networks. I imagine you could work something out with the engineers so the receiver does not make assumptions about the incoming data's clock speed. That's just an engineering problem.

    Of course, for sufficiently high speeds you may need a different kind of receiver completely.

    In this example, the transmission was by prior arrangement - how you pick out a signal when there was no prior arrangement is a SETI problem innit :) Normally you'd know the relative speeds anyway.
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