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Tachyonic antitelephones in a FTL-universe?

  1. Jan 7, 2015 #1
    In some threads here and on other forums it was mentioned that a universe could have no upper speed limit only if it had a preferred frame of reference as opposed to "our" relativity.

    I'm wondering to what degree could such a universe be designed to "mimic" our own? Could there be a phenomena similar to the Lorentz factor and its consequences (magnetism, blueshift et cetera) but without actual relativity?

    I want a universe where different frames of reference doesn't lead to time-travel. I have this idea that physics, chemistry etc looks "normal" (but of course isn't) until someone tries to simulate FTL by actually performing the tachyonic antitelephone experiment, but could this be done with "faked" FTL instead of an actual FTL signal, say two devices distanced "n" from each other switching on within less than n/c time interacting with a beam of "relativistic" particles or something?
     
  2. jcsd
  3. Jan 9, 2015 #2
    I think there is a very similar topic in the writing subsection.
    With FTL one sure cant avoid see the past, the question, whether is that particular universe allows to alter it, or it remains read only?
     
  4. Jan 9, 2015 #3

    Drakkith

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    I think the easiest way is to just invent a way to travel FTL and assume that relativity is wrong in that regime. For example, our current understanding is that if you exceed c, you can travel backwards in time. This is easily circumvented by saying that relativity is wrong when it comes to FTL velocities and then invent whatever rules you want. Perhaps time is not something which has an absolute past or future and you can't travel to the past because it really doesn't exist anymore.
     
  5. Jan 10, 2015 #4
    "Perhaps time is not something which has an absolute past or future and you can't travel to the past because it really doesn't exist anymore."

    Well, exactly what i think, we can see the past of distant stars, but i cant imagine that there is any way to change what has already happened with them.
     
  6. Jan 11, 2015 #5
    If time slows down objectively for an object moving at relativistic velocities, then I'm thinking there must be some kind of "modifier" to ensure that common phenomena like magnetism, diffraction and so on doesn't end up "reversed". The moving observer in this non-relativistic universe will inevibably see the rest of the universe as being sped-up.

    I'm failing to find it, care to link?
     
  7. Jan 12, 2015 #6
    https://www.physicsforums.com/threads/ftl-avoiding-time-travel-issues.761008/

    "The moving observer in this non-relativistic universe will inevibably see the rest of the universe as being sped-up."

    Well, if a relativistic ship with sqrt(3)/2c goes to Alfa Centaury, due to time dilation, it can measure roughly two years of travel (as if it were only two light years away) they age half.
    (At SF travel, local speed isnt beyond light, spacetime itself warped.)
     
    Last edited: Jan 12, 2015
  8. Jan 16, 2015 #7
    Wormholes are compatible with relativity. If you want to avoid closed timelike curves, you can require that all wormholes must be non-moving with respect to the cosmic microwave background.
     
  9. Jan 16, 2015 #8
    If I've understood it correctly, if you "Mink" (use a Minkowski diagram) on what happens when a relativistic observer passes between the wormhole mouths, a CTC still appear. If the observer moves fast enough, it will observe that an object exits a wormhole mouth before entering, and the observer could also drop a bag of cat-sand or something to interfer with the object entering.
     
  10. Jan 16, 2015 #9
    "and the observer could also drop a bag of cat-sand or something to interfer with the object entering."

    If the observer is co-local with the entry point, than delay time of light coming from the end point cant be ignored. If not co-local, signal delay time comes into the image. I fail to see how you get a negative delay time on the end, after sum up everything.
     
  11. Jan 17, 2015 #10
    A wormhole basically gives the the same result as any other FTL though instead of a continuous linear function that has a lower k than "1" (=higher velocity) the result is a non-continuous function. Information still moves faster than the light cone, and voilá, CTC's pop up, that the function doesn't actually go through the intervening space-time doesn't matter. The moving observer could be a minimal distance from the mouths, depending on the relative velocity of the observer and the distance between the mouths the perceived difference in time between event and cause could be huge.

    I'll see if I find a good guide to this, I'm pretty sure I learned it from a page where the exact scenario (moving observer, wormhole mouths not moving in relation to each other) was mink'd and gone through stepwise.
     
  12. Jan 17, 2015 #11
    Vemvare, the standard anti telephone requires wormholes that are moving relative to each other. If the wormhole exit is comoving with the entrance, there is no way to get from the exit back to the entrance before you entered. This is obvious if you stay in the reference frame of the wormhole. If the distance between the entrance and exit is d, it will take at least d/c to get from exit back to entrance.
     
  13. Jan 18, 2015 #12
    But how then did you create a distance between the two wormhole mouths in the first place? If they can't move in relation to each other, they're kind of useless unless some really, really low probability quantum fluctuation that randomly connects just the two points you want could be used at distances... kind of larger than the Planck length, as in light-years larger.

    I've started a thread in the more serious part of the forum to see if anyone can help me/us with this.
     
  14. Jan 19, 2015 #13
    "I'll see if I find a good guide to this, I'm pretty sure I learned it from a page where the exact scenario (moving observer, wormhole mouths not moving in relation to each other) was mink'd and gone through stepwise."

    I didnt find graphs (but i would gladly see them) that dealt with the problems of A : light delay time
    B : http://en.wikipedia.org/wiki/Relativity_of_simultaneity So, based on the direction of the moving of the observer, either A or B can happen earlier.
    If that observer cant move opposite directions at once, why is it, that the message wont go even faster forward in time, when goes back to the first sender?

    Thought experiment : i have two atomic clocks. Set A to alert at T+0ns, T+2ns, set B to T+1ns.
    I separate them far away with the same acceleration and speed.
    If they are far away, then as far as i managed to understand simultaneity, i think the following things can happen : yes i can find a viewpoint where B event happens before As T+0ns. But then it will observe an even bigger difference between Bs T+1ns and As T+2ns.

    I have the magic FTL ship, escape from Alderaan before its destroyed. Jump a light year away, great it is intact again. Time to save people.
    When i go back, it will be space debris again.
    (Well, the part that all observers should agree about the order of casually connected events, will be surely violated in that other universe, we cant send FTL signals in reality...)
     
    Last edited: Jan 19, 2015
  15. Jan 23, 2015 #14

    Ryan_m_b

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    Your question is unanswerable the moment you include something like this. You're basically asking how the laws of physics would work if they didn't apply.
     
  16. Jan 23, 2015 #15
    My point is, once one includes any kind of FTL in his SF universe, IMHO it is rather pointless to speculate about whether it is casual in our reality or not, whether relativity has to be thrown away in STL cases also, or not, whether static wormholes different from moving ones or not, since that fictional universe is different from our known reality to begin with. That is a story, not a scientific publication, one has got hyperspace, fine, it doesnt make much sense to ask, how to enter hyperspace in reality, and will i go back in time also? At least, as a reader, and would be writer, and curious amateur about physics, i think that.
     
  17. Jan 24, 2015 #16
    Well, in that novel I've been working on (yeah, I know) the protagonists are indeed in another universe, and realize this when an experiment gives a result that doesn't make sense if there is no absolute frame of reference.
     
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