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Timetraveller killing himself in the past

  1. Nov 18, 2011 #1
    Say timetravel was invented, with wormholes for example. And a 27 year old guy decided to go back in time to when he was 12. He would shoot and kill the 12 year old self.
    Or in another case, he goes back to when he was not even born yet, and kills his mother.

    What would happen to the traveller? Would he just continue on existing, and his death at younger age would just happen in "a parallel universe", or would he cease to exist?
    If its the ladder, which seems odd to me, then HOW would he cease to exist? You cant just vanish, right?
    Also, when you go back in time, are you not adding mass (the atoms you consist of) to the "past universe"?

    Thanks in advance,
  2. jcsd
  3. Nov 18, 2011 #2


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    I guess those who claim to believe in the possiblity of timetravel are pulling the wool over your eyes. I wouldn't pay them any more money if I were you.
  4. Nov 18, 2011 #3


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    Yeah, I am perfectly willing to explore the math of the singularities and closed timelike curves that GR allows, as well tachyons that can be made mathematically consistent with SR. Yet I would happily bet a large sum that none of these exist in the real universe.
  5. Nov 18, 2011 #4


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    Macbeth. Or more accurately, Macduff.
  6. Nov 18, 2011 #5


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    If find the following paradox much more amusing and challenging than shooting yourself/parent in the past. One reason is that things like Novikov consistency preclude many paradoxes but not the following (which Greene argues you just must accept, but I don't):

    I go back to Shakespeare's time and discover he has some idea about the play Macbeth, but has writer's block and can't get it going. You give him a copy of Macbeth, he loves it and produces it (no plagiarism, since he wrote it). So who really wrote Macbeth?

    None of the main consistency or 'censorship' hypotheses prevent plays, symphonies, etc. that have no causal creation. This is enough for me to conclude these ideas are simply garbage and don't occur in the real world.
  7. Nov 18, 2011 #6
    Imo, the whole grandfather theory is wrong. The moment you travel back in time, the physics and matter would have all changed at that point. You are now a new living thing at that time.
  8. Nov 18, 2011 #7
    it's a continuum. There's no going back. this is it. no worm hole. in a smbh all matter squashes to subatomic, then pure energy to an exit - so no traveling through time. tomorrow is a new day, forget the past. trekies.
  9. Nov 18, 2011 #8
    fawk3s, for a very good popular book by a physicist that discusses these "bootstrap" and also the potent "no choice" paradoxes, see:

    "Black Holes, Wormholes & Time Machines" by Jim Al-Khalili
  10. Nov 18, 2011 #9
    Yeah, if backwards time travel were possible, that begs the question, "Where are the time travelers from the future?"

    On the other hand, time travel to the future is easy and doesn't violate conservation of mass/energy.

    You just have to travel at a velocity far greater than anything else in the Universe.
  11. Nov 18, 2011 #10


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    Just because GR admits solutions with closed time-like curves, doesn't mean that they exist. At the end of the day, GR is still a mathematical model, and with all mathematical models we must interpret them correctly.

    Just because the math says something, doesn't mean it exists. Experiment should be the ultimate judge.
  12. Nov 18, 2011 #11


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    This is entirely speculation and so does not belong her on PF.

    It just occurred to me how time travel could occur without creating any grandfather paradoxes.

    By traveling through time you end up outside your own light cone. That means that after the trip through time you end up back in the same time as before, but you can't have a cause-effect relationship with anything in your own past. i.e. you cannot go back an kill yourself because you will arrive too far away that you couldn't get there at any speed less than c.

    It also just occurred to me that I'm not the first person to think of this.
  13. Nov 19, 2011 #12
    Well, it has never happened so we just plain don't know. The adding mass to the past universe seems odd to me too, but if it were done then that would be that.

    Even it it DID happen maybe there is some reason we don't know it happened, or we know it happened but we don't know how, or... who knows?
  14. Nov 19, 2011 #13


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    Hmm... Imagine that the book sent from the future is... 20 tomes of a detailed universal history. Imagine that it comes in electronic format and it is uploaded in the internet in a public server, so everybody can read it. So far, so good, still history has not changed. But what a hard job would the censors have in preventing people from changing it...! :devil:
  15. Nov 19, 2011 #14
    This is nothing more than the "multiverse" theory, IMO.
    You go back in time, but from then on, you're in a different universe.

    Still doesn't answer the question, "Where are all the time travelers from the future?"
    You'd think one or two would've shown up by now, considering the fact that accelerating expansion of space implies no end to the future other than heat death.

    Who exactly gets to determine what is or is not "entirely speculation" that "does not belong her (sic) on the PF"?
    I don't envy that person(s), him or her. LOL
  16. Nov 19, 2011 #15


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    The types of time travel machines that are permitted by GR do not allow time travel to points before the construction of the device. So the answer to the question "Where are all the time travelers from the future?" is simply that the time travelling device has not yet been built so the time travelers cannot travel to now.
  17. Nov 19, 2011 #16
    Say perpetual machine was invented... but not in this universe.
  18. Nov 19, 2011 #17
    Think about what you are suggesting. If a 27 year old guy went back in time he would get younger and unlearn what he had learned in the intervening 15 years. He wouldn't be a 27 year old guy looking at a 12 year old kid. He'd BE that 12 year old kid.

    What you are really suggesting is that the 27 year old guy continues moving forward in time, but the rest of the universe goes back in time 15 years.
  19. Nov 27, 2011 #18
    no this is not correct you are talking in the same time frame
  20. Nov 27, 2011 #19
    The distortion unit reaches its target destination by using very sensitive gravity sensors and atomic clocks. The basic unit of calculation is the second. So yes, in a sense you do “dial in” in a date and the computer system controls the distortion field. At maximum power, the unit I have is capable of traveling about 10 years an hour.

    Unfortunately, time travel is not an exact science. There is inherent error and chaos in the computers ability to make accurate calculations. Based on the current technology of the clocks and sensors, distortion units are only accurate to about 60 years or so. So no, . The divergence between the worldline of origin and the target worldline would be too great. If one were to try and travel back that far, history would look nothing like what you would expect.
  21. Nov 27, 2011 #20
    Your answer is that a 100 year old theory doesn't allow it?
    Not very convincing.
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