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Time in relativity and quantum mechanics

  1. Dec 7, 2015 #1
    this question is a bit philosophical...

    in general relativity time "doesn't exist", and all of spacetime is already a preexisting pseudo riemannian manifold. however experiments have only shown time run at different rates, not that spacetime is preexisting.

    in our ordinary experience time is like a flowing river and we are like boats being carried by the flow, and future is "created" as we go along. quantum mechanics also supports this view of time, the future is created as we go because wavefunction collapse is random.

    https://en.wikipedia.org/wiki/Problem_of_time

    how do these two contradicting things make sense? is our understanding of time far from complete? i dont understand the stuff about hamiltonian in the wikipedia article so can someone give me a non technical explanation thanx
     
  2. jcsd
  3. Dec 7, 2015 #2

    phyzguy

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    The two explanations are in conflict. Hence the name Problem of time.
     
  4. Dec 7, 2015 #3

    bcrowell

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    The words you're using, such as "preexisting," "flow," and "created" don't have clearcut meanings in this context. If your question were to be a meaningful one, you would have to define these words.

    No, quantum mechanics does not say anything about wavefunction collapse. That's the Copenhagen interpretation (CI), which is a philosophical thing that's not testable by experiment. There are other interpretations, such as the many-worlds interpretation (MWI), in which there is no wavefunction collapse. CI and MWI do not make different predictions about experiments, so they are not physical theories and are not part of quantum mechanics.
     
  5. Dec 7, 2015 #4

    PeterDonis

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    Note that this Wikipedia article is flagged as needing attention from an expert. That's a good indication that it's not giving you a very good explanation of the issue.

    The basic issue is that there is no general way to describe the "total energy" of a curved spacetime in GR. But in QM, the total energy, i.e., the Hamiltonian, is what determines the time evolution of quantum states. So if we take GR and QM at face value, they are incompatible, because GR gives us no way to describe the quantum operator that determines time evolution. There are various speculations on how to address this issue, but no good answer as yet.

    Quite probably, yes.
     
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