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Time travel (of information)

  1. Dec 22, 2003 #1
    Is it theoretically possible to encode information in particles which travel back in time? I realize this is a can of worms question. I am also not too sharp with QP. Isn't there a theory in Quantum Physics that there are "forwards" and "backwards" photons which meet each other in time? So I am wondering if data could be carried that way.

    Feel free to speculate. I'm writing a story and I am simply looking for a general excuse for a hypothetical device being able to send back messages in time. So the audience won't care whether the theory holds up in a room of qualified scientists, only whether it sounds "believable" that messages can be sent backwards.
  2. jcsd
  3. Dec 23, 2003 #2
    Umm... hello?

    I know there is a separate area for Time Travel posts, but this really does relate to QP. Does anyone understand my question? or should I have posted it somewhere else?
  4. Dec 23, 2003 #3
    The uneasy coexistence

    Although some interpretations of QM postulate signals that travel instantaneously (as in Bohmian mechanics) or back in time (as in the transactional interpretation) these are by no means universally agreed upon. Also, QM exhibits something which has been called the 'uneasy coexistance' with relativity. This means that although it is possible to use signals that travel faster than the speed of light to explain some phenomena, these can NEVER be used for communication. This is shown by the so-called 'no-signalling' theorem.

    Your best bet for time travelling signals, if you want to make them scientifically plausible, is to make use of general relativity (via wormholes) and possibly the many-worlds interpretation of QM in order to avoid time travel paradoxes.

    However, there has never been a strict requirement that fiction should be scientifically plausible in the first place. Despite the fact that series such as Star Trek employ scientific consultants, devices such as 'inertial dampers', 'transporters' and 'replicators' remain highly dubious from a realistic perspective. Therefore, I suggest you use whatever sort of device is needed to make your story work.
  5. Dec 24, 2003 #4
    Re: The uneasy coexistence

    I totally agree with all of slyboys answer but the suggestion about wormholes leaves me cold.. It is SO overdone. Nearly all Sci Fi writers, TV programme makers etc use the 'wormhole' solution. It is a bit of a cop out really, I think.

    In class (I teach Physics), all I ever hear when we discuss BB Theory, QM, Relativity, etc is 'wormholes wormholes wormholes...!" I'm SICK of hearing about bloody wormholes!

    So, if you do use 'wormholes' yes, your audience will be familiar with the idea, but why not think of a new idea - it will make your work standout from the rest.
    Slyboys last paragraph is spot on!
  6. Dec 24, 2003 #5
    Hey, thanks, guys. I think I know what you're talking about, slyboy, when you say that no signalling is possible. That's a shame.

    I will still look for some rational explanation, though (I wanted the story to be just a little more plausible than Star Trek pseudo-science). Wormholes are a possibility, but a little cliche, as Adrian Baker pointed out. Well, you've given me something to think about. Back to the drawing board, I guess. :)
  7. Dec 24, 2003 #6
    Rudy Rucker likes to use causal loops for this kind of thing and materials in which light appears to travel faster than the speed of light in a vacuum (see his short story collection 'Gnarl').

    Although most physicists agree that none of these things can be used to signal faster than light, there are a few loopholes in current theory and experiment that might be exploited. Recently, experiments were done to test no-signalling using these sort of materials and the findings supported the consensus view, but they were not entirely conclusive.

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