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B Time travel with tachyons cause infinite dilemma?

  1. May 15, 2016 #1
    Hi. Im a 13 years old and interested in particle science. I was reading on tachyons and how you could hypothetically send them as signals back in time (not that I'm saying we will manage anytime soon or ever). It got me think about it and I realized something. I'm sure somebody has heard about this.

    Say you can travel back in time. What if you kill your father when you go back in time. This would lead to you wiping yourself from the timeline, since you killed your father. However, if you never lived due to the fact that you killed your ancestor, you would have never killed him then. Resulting in the timeline resuming to the original one. Which would cause you to be alive. If this some infinite pattern?

    Thanks! (Sorry if this is a stupid question: just curious).

    NOTE: My prefix is not my actual grade: just had to put something there.
  2. jcsd
  3. May 15, 2016 #2


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    Your description shows why most people say backwards time travel is impossible.
  4. May 15, 2016 #3
    I'm not saying that it is possible to send a message back in time. But if it were, you could not use it to kill yourself or do anything else that would stop the message from being sent. The fact that you are alive and able to send the message is evidence that the attempt failed.

    So if you traveled back in time and tried to shoot your father, you would fail. Perhaps you hit the wrong guy.
  5. May 15, 2016 #4
    Hello there and welcome on the forum! Time travel causes those paradoxes, yes. In my opinion, such time travel is impossible for that reason. However, in quantummechanics there is a way to associate information in the past with information in the present or future. This is called 'non-locality'. However, this doesn't make actual time travel possible. This has to do with that you have to send information back in time (ie. yourself) to be able to travel in time, and that is not possible in QM. So you won't have to worry you mess up some timelines. :wink:
  6. May 15, 2016 #5


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    You're fine on the prefix. It's not your educational level, it's the level of answer you're looking for.
  7. May 15, 2016 #6


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    Be aware that tachyons (meaning particles that move faster than light) are themselves hypothetical. There is no reason to believe that they do exist and many reasons to believe that they do not.
  8. May 15, 2016 #7


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    Your proposed paradox has been discussed ad infinitum in science fiction and on this kind of forum for decades. Do a forum search, you'll find a lot of discussion. A good place to start is probably with the links at the bottom of this page.
  9. May 16, 2016 #8
    Thanks! I checked them out.
  10. May 16, 2016 #9
    Of course. Even if they did exist, theoretically, they would have a negative mass. Although I thought: "Photons have been proved to have mass since only thing that have mass can be affected by gravity (supposedly in dark matter and black holes - not that I'm confusing them: they are not the same). So could tachyons have an even lower mass since you can go into infinitely small decimal?
  11. May 16, 2016 #10
    Cool. So "destiny" would stop you from doing so. Makes sense.
  12. May 16, 2016 #11


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    Photons do not have mass. They are massless to within the limit of our measurements. There is no rule in physics saying that only objects with mass are affected by gravity. Note that you will almost always see equations relating to gravity as having an 'M' for the mass of an object, but that's only because almost everyone having to take the force of gravity into account is working with objects having mass. Very few people have to calculate the change in the path of light due to gravity. The only ones I can think of are astrophysicists and perhaps a handful of engineers working on special light-related projects. Maybe for NASA or something.
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