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B Are time loops possible?

  1. Oct 27, 2018 #1
    I haven't been on here in a while and have forgotten a lot of my physics knowledge, which is annoying.

    I just want to know, are time loops possible? Like the ones that appear in movies where a character relives a period of time. Is this allowed by the laws of physics? I know it's not really a physics question but this stuff is important to me, if someone with knowledge of physics is able to explain it. Thanks.
     
  2. jcsd
  3. Oct 27, 2018 #2

    Mister T

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    Do a google search for closed timelike curves.

    Note that the worldline of a person is a timelike curve, so if it were close it's hard for me to make sense of the concept of time.
     
  4. Oct 28, 2018 #3

    Ibix

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    No.

    Mathematically, we can describe "loops" in spacetime where you can pass the same event twice, but that doesn't operate like Groundhog Day. Every other time you went round the loop would be present every time. And all the potential for paradox that implies lead Novikov to propose his consistency principle, which boils down to "you can't change anything".

    Furthermore, although we can describe such structures mathematically, the conditions necessary for them to actually exist are impossible as far as we know (negative energy densities and the like).
     
  5. Oct 28, 2018 #4
    Interesting. So, what's really happening in the movie Groundhog Day? Is it anything of physics or just magic?
     
  6. Oct 28, 2018 #5

    Nugatory

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    Fun movie, zero physics content.
     
  7. Oct 28, 2018 #6

    Ibix

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    Magic. I have trouble imagining a physical model that could measure Bill Murray's character development and stop the loop when he had done enough to get the girl.
     
  8. Oct 28, 2018 #7
    Ok, I understand, but I know this sounds crazy, but my friend keeps insisting he lived a day multiple times like the movie Groundhog Day. Why would he say that?
     
  9. Oct 28, 2018 #8

    Ibix

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    Drunk, stoned, delusional, pulling your leg?

    Remember Occam's Razor.
     
  10. Oct 28, 2018 #9
  11. Oct 28, 2018 #10

    Nugatory

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    Staff: Mentor

    Your question was answered in post #3 above.

    The thread is closed.
     
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