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How does quantum mechanics define time

  1. Feb 3, 2013 #1
    How does quantum mechanics define time if there is any definition, or quantum gravity has to be explained first?
  2. jcsd
  3. Feb 4, 2013 #2
    Quantum mechanics say that every particle is a clock. Its space-time ticks are given by the energy and momentum T=h/E and \lambda = h / p. This set time in physics, as discussed in How a particle tells time (Holger Mueller et al in *Science*) and
    Example: In relativity the rest energy is the mass E= m c^2. Light has zero mass so the ticks of photons are infinitely long. Light has not time.

    These clocks define time in quantum mechanics.

    Einstein says that interaction is modulation of clocks. He derived general relativity in this way. Quantum gravity should be explained from these aspects of quantum mechanics and general relativity.
  4. Feb 4, 2013 #3
    Carlo Rovelli has this to say about that:

    Unfinished revolution


    "Forget time"
    Authors: Carlo Rovelli....
    (Submitted on 23 Mar 2009 (v1), last revised 27 Mar 2009 (this version, v3))

    [Nobody has figured out how the dynamical spacetime of GR can be incorporated in the Standard Model...quantum gravity theoryies are attempting to reconcile these differences.]

    from one of those papers:
  5. Feb 4, 2013 #4
    Thanks, I will examine this.
  6. Feb 6, 2013 #5
    There was recent article in FQXi Blogs discussing this dichotomy based on some works by Andreas Albrecht. Some interesting quotes relevant to this thread:
    The Accidental Universe

    His Perimeter presentation can be found here:
    The Clock Ambiguity and the Emergence of Physical Laws
    http://streamer.perimeterinstitute.ca/mediasite/viewer/NoPopupRedirector.aspx?peid=1a12ed6d-3993-49f7-a9ce-0dd154f38e84&shouldResize=False [Broken]
    Last edited by a moderator: May 6, 2017
  7. Feb 6, 2013 #6


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    Quantum mechanics doesn't say anything about time. Galilean spacetime and Minkowski spacetime define mathematical frameworks in which both classical and quantum theories of matter can be defined. Time is described by spacetime, not by a theory of matter, at least not by any of these theories of matter.

    I think even the GR spacetimes define such frameworks. The problem is just that if we first find a spacetime that satisfies Einstein's equation, and then write down a theory of matter in that spacetime, we are completely ignoring the main lesson of GR, which is that matter should affect spacetime.
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