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Tachyons, the Double Slit Experiment, and a bit of Fiction

  1. Dec 1, 2015 #1
    Hello, All!
    I'm writing a bit of fiction, and as a newcomer to the world of Quantum Physics, I thought I'd clarify a few concepts here, to avoid lapsing into technobabble. I'm trying to make something along the lines of the film Primer, which tries to incorporate as much realism as possible within the premise.
    For the purpose of this discussion, please understand that I'm not asking if what I'm suggesting is possible in reality. I'm ONLY asking whether, if each of the suppositions I'm making (the existence of tachyons, etc.) WERE true, what I'm suggesting would be plausible.
    Let's start at the beginning moving forward-
    To my understanding, the double slit experiment works as follows: When an electron or other particle is fired at an intervening object with two slits in it, and impacts against a backstop capable of detecting it, it's impact appears to be determined by probability. That is to say, rather than simply landing in one of 2 areas corresponding to the slots like a solid particle, it instead lands as though it were a wave- in an interference pattern determined by probability.
    If the experiment is modified by placing a detector over one or both of the slits, it seems to affect how it behaves. It is as if the act of measuring which slit has altered the probability of where the particle lands, reducing it so that rather than appearing to fall as an interference pattern, it lands more directly on the far side of either slot.
    According to theories supporting wave function collapse of superimposed states, this is because the act of observing it defines its path, causing it to fall where the observer would expect. With the variations on detector placement, some even question whether it causes retroactive changes in the behavior of the electron in question, causing it to behave as though it had been following that clearly defined trajectory all along. Regardless, they say that once it collapses, that is reality, and the other states simply cease to exist.
    Proponents of 'many worlds' style theories say that the wave function does not collapse to a single reality, and that it simply decoheres, and we're only capable of seeing one possible outcome.
    Would it be fair to say that those outcomes are still determined by probability?
    And now, for the sci-fi part...
    Suppose that tachyonic particles existed, possibly electrons somehow accelerated to superluminal speed. If we could somehow perform the double slit experiment with them, would we see them generated in an interference pattern, then travel back through the slits to the source?
    If we had a monitor, as with the variant on the double slit experiment, would they appear to emanate from the two areas directly beyond the slit rather than in an interference pattern?
    Thanks for your time! Like I said, this is fiction, so please no responses informing me that tachyons can't exist, etc. Just looking to make sure I've described the theories correctly and that my hypotheticals make some kind of sense!
  2. jcsd
  3. Dec 1, 2015 #2
    By my rather primitive knowledge, you seem to have an understanding that is reasonably close to the way many people think.

    The part that bothers me is this

    If we could somehow perform the double slit experiment with them, would we see them generated in an interference pattern, then travel back through the slits to the source?

    We wouldn't be able to see them traveling at all. In the double slit experiment we can't ever see the particles or whatever traveling. If we could detect them while traveling, then no interference pattern could be generated.
  4. Dec 1, 2015 #3
    So far, so good.

    Completely covering a lit with a detector will do that, but the "magic" happens when you allow the particle to pass through the slit - but detect which slit it went through. Then you get two blurry blobs, one from each slit, and no interference pattern.

    If you determine which path (which slit) the particle passed through, there will be no interference pattern. If you do not determine its path, it will behave as though it went both ways.

    There is an experimental setup called "delayed choice erasure" where you are free to interpret the result as an interference pattern and a non-interference pattern being formed before a "decision" is made on whether the which way information will be collected. However, that's only an interpretation someone would make after studying the setup and results closely, recognizing the paradox being demonstrated, and then doing the best they could to describe the result in classical (non-QM) terms.

    Ok. But one particle does not an interference pattern make. You collect scores of particles and the accumulated result of these many collapses show the interference pattern.


    Of course, there is no known road to superluminal speed - but acceleration isn't it. Let's just say you have a detectable tachyon - manufactured by whatever story you prefer.

    A detectable tachyon could appear to be travelling backward through time from some reference frames. So that would be a possible viewpoint.

  5. Dec 1, 2015 #4
    Thanks to those who have replied so far!
    To give a clearer picture of what I'm trying to deal with, the story revolves around a group of physicists trapped in a room with a specialized 'camera' and several monitors. The monitors are each displaying an alternate version of reality occurring approximately 10 seconds in the future.
    The idea is that someone has designed a way to fire tachyons, then use the 'camera' to read them and decode them as an image.
    Since the tachyons have a single source, but have each struck a different 'probability' point in the future, hence the reason why the signal is decoded and split into several images showing different outcomes limited by probability based on what is occurring in the present.
  6. Dec 1, 2015 #5

    Sure, that's good enough for science fiction. It's cool.
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