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Time Travel Paradox

  1. Dec 28, 2011 #1
    I just got done watching Stephen Hawking's Into the Universe episode 2, which is about time travel.

    They think that time travel into the past is most likely impossible simply because of paradoxes (go back in time, and kill yourself before you went back in time).

    However, tiny wormholes the size of an electron open up all the time, allowing matter to go through time. Wouldn't it still be possible to build a machine that would try and detect this electron, and kill the machine's operator before they sent it back in time?

    And what do you guys think might happen if a paradox like this DID occur?

    Please move this thread if it's in the wrong section, thanks.
  2. jcsd
  3. Dec 28, 2011 #2


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    This is incorrect. Where did you hear this? Do you have a citation?
  4. Dec 28, 2011 #3
    I'm thinking that time slowing down as a result of velocities approaching lightspeed, etc, is not the same as going backwards in time.

    I believe that time goes on no matter what we are doing, and that the people in the past do not have to re-enact what they were doing every time a time traveler popped over to visit.

    So if you left on an interstellar journey at ~ lightspeed, and returned to earth later, maybe earth would have experienced more time than you had, but you can't go back and see something that already happened....only whatever is happening when you do come back. IE: You are always in the present...your journey's route may differ, but when you get back to earth, it will be in whatever the present is...and what is happening when you get there is happening for the first time.

    This would mean that all of those paradoxes where you travel back and kill yourself would have already happened, and you would not have been there to do it, and of course, therefore, it never happened. A 30 yr old man can't go back and kill his 12 year old self, as that 12 yr old would have already been killed...as you are only 12 once.

    So time travel is not impossible because of the paradoxes, the paradoxes are impossible because you can't travel back in time.
    Last edited: Dec 28, 2011
  5. Dec 28, 2011 #4
    As I said, Into the Universe episode 2, which is now my favorite science show. Here:


    If it's incorrect, then oh well, that's why I didn't post this in a more scientific part of the forum.
  6. Jan 4, 2012 #5
    Time travel to the past has to be impossible; it creates paradoxes, effects before causes. These cannot exist logically. For this reason I am in agreement with Stephen Hawking on the subject.
  7. Jan 4, 2012 #6


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    I guarantee you that this is not true. At minimum we don't even know if it is possible. There is zero evidence of tiny wormholes opening up, swallowing subatomic particles, and spitting them out somewhere else in time. We don't know if wormholes even exist yet.
  8. Mar 4, 2012 #7
    Well...i too disagree with your wormhole thing. First of all they are too unstable. They will destroy themselves before you go in and pop out your head to another region of space-time. But the newest discovery of neutrinos that can travel faster than light can still give a ray of hope. But even this is vulnerable. Even if you travel faster than light...it would cause an effect on your personal arrow of time., not the cosmological arrow of time. Get it?
  9. Mar 4, 2012 #8
    Well Drakkith you are absolutely correct. This is no experimental proof of wormholes. It was just an assumption as Einstein's field equations gave rise to an Einstein-Rosen Bridge which could connect two parts of space time. There is no evidence of their existence. Its just an idea.
  10. Mar 5, 2012 #9
    I don't understand quantum physics too well, but I believe when we're talking about particles the size of electrons, there are lots of logical paradoxes, such as it existing in two places at the same time, or existing and not existing simultaneously.

    My point is that even if a wormhole opened up and sent the electron back in time, "a machine that would try and detect this electron, and kill the machine's operator before they sent it back in time" is perhaps not as problematic as it first appears.
  11. Mar 5, 2012 #10


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    There has yet to be a consensus about FTL neutrinos. In fact, they just discovered two faults in the equipment, meaning that their data is currently questionable. Hopefully they can fix it and still use the data. Once that happens or another experiment is run we can find out more.
  12. Mar 5, 2012 #11
    Existing in two places at once is not, in itself, a logical contradiction. There is nothing that has ever been observed that both exists and doesn't exist simultaneously in the same way (I don't think there is anything like that theorized either). Logical consistency is a requirement for any mathematical model, whether it accurately represents actual processes or not. That is the problem with changing the past, it would require at least one event to have a state of both having occured, and not having occured at the same time and in the same way. Thus, it is impossible to change one's own past (no matter what theory one is working under). This does not mean that time travel is impossible, just some naive notions of it (e.g., most instances in films or on TV).

    Note that I have not made any reference to a specific physical theory, the above restriction(s) are the bare minimum for any theory. The actual restrictions on time travel may be more stringent (perhaps so much so as to exclude it from being possible).
  13. Mar 5, 2012 #12


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    In some pictures of quantum field theory, particles can move back in time, forward in time, or even move in the space direction (in essence, being in multiple places at once). These time-traveling particles are called virtual particles. Virtual particles can't be directly observed since they only appear over a short time. What is observed is the effect of a superposition of an infinite number of possible arrangements of virtual particles. You might say virtual particles are just some artifice of the mathematical model, but, could you not also say that real particles are also an artifice of the same mathematical model?
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