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I Chronology protection conjecture and Tachyonic Antitelephone

  1. Apr 21, 2016 #1
    Now, first off I am punching well above my weight here but oh well. I am doing an extended project on theoretical methods of space travel and was doing some brief reading in the middle of writing about Miguel Alcubierre's warp drive for hyper fast travel within general relativity. I came across the suggestion of using tachyonic particles which lead me to the tachyonic antitelephone. It said that this would possible violate causality, firstly I do not fully grasp causality I don't think so an explanation of this as simple as possible would be nice, secondly, I know that the warp drive is suggested to violate causality but is affected by the chronology protection conjecture as to prevent closed timelike loops, does this same principle not apply to the tachyonic antitelephone? What I have said may just be a load of rubbish as as I say I am just a bit out of my depth but worth a try.

    Thanks in advance
    Falcus
     
  2. jcsd
  3. Apr 21, 2016 #2

    mfb

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    Staff: Mentor

    Imagine you follow this thread for a while, after some time you decide that the question has been answered, and send back all that information to you yesterday. As you (yesterday) knows the answer, you do not create the thread. But the thread exists...
    Alternatively, imagine someone now sends you the text in the first post to you in the past, and imagine you just copied it to create the thread. Who wrote the thread?

    There are a few possible solutions to this problem:
    - self-consistency: something prevents you from sending the information back in time, or even if you do you still start the thread for some reason. Inconsistent universes cannot exist, therefore the universe is consistent
    - causality: chains like "A leads to B leads to A (or not A)" do not exist (chronology protection conjecture)
    - those time travel things lead to alternative timelines in some way
     
  4. Apr 21, 2016 #3
    Say there are two events, A and B, and according to you A causes B. So for instance A could be someone throwing a switch at one location and B could be a light coming on at another location. It can be shown that if the transmission of the signal from the one location to the other travels faster than the speed of light, then there exists another frame of reference, traveling at some speed relative to you, for which event B occurs before event A. That violates causality - in that frame an observer would determine that the light came on before the switch was thrown.
     
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