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A QM's interpretations vs GR

  1. Mar 18, 2018 #1

    MathematicalPhysicist

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    As far as I can tell QM has several interpretations, but GR doesn't have such a diversity, am I correct?

    Why is that?
    Will a theory of QGR suffer also from the disease of QM and will yield several interpretations?
     
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  3. Mar 18, 2018 #2

    Orodruin

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  4. Mar 19, 2018 #3

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    Because GR is an ontological theory. Space-time curvature is supposed to be there even if nobody measures it.
     
  5. Mar 19, 2018 #4

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    And in QG, is it still there when no one measures it?
     
  6. Mar 19, 2018 #5

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  7. Mar 19, 2018 #6

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    It depends on the interpretation of QG. In other words QG, by itself, does not resolve the interpretation problems of QM.
     
  8. Mar 19, 2018 #7

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    What do QG theories tell us about the measurement of curvature of spacetime?

    I mean on the one macroscopic scale (which its limits need to be defined strictly contrary to microscopic and mesoscopic scales) limit the curvature should be there whether someone is measuring or not, but on the quantum regime which is microscopic we have the measurement problem, the curvature may not be there if no one is measuring it.

    Another question which seems rather vague but interesting nonetheless.
    Can individual particles measure macroscopic entities?

    I mean, an observer performs a measurement on particles, assuming he is composed of several particles, then it seems like an ensemble of particles can perform a measurement on single particles, can the vise versa process occur?

    How do we even define the notion of "measurement" coherently?
    I mean even in non-laboratory conditions we make measurements all the time in this dynamical world.
     
  9. Mar 19, 2018 #8
    I like the view that "measurement" is a process where measuring apparatus becomes quantum-entangled with the measured object. Depending on the design of the apparatus, entanglement with different parameters occurs.

    It's the Schrodinger's cat all over again: cat measures the state of the radioactive atom. Similarly, a CCD camera measures arrival of a photon. When photon from a distant star hits a CCD detector, now you have your CCD in a superposition of states, in each state one of its CCD cells has a trapped electron. As soon as you observe (nee "measure") your CCD, now _you_ and the CCD are in a superposition of states of seeing a CCD with a particular cell having that electron.
     
  10. Mar 19, 2018 #9

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    The question is more like: who is the one making the measurement, the observation; I mean with your definition all the universe can be seen as entangled, I mean one parameter you measure here will have some correlation with a parameter observed by some other scientist in alpha centauri for example.
     
  11. Mar 20, 2018 #10

    Fra

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    I agree this is a key question. The question you raise here is, how to describe a "cosmological measurement", which is effectively what you have when a small inside observer wants to "measure" something in a dominant environment.

    It is clear that the abstraction used for scientific measurement, and statistics in particle physics which is clean, mathematical precise and allows us to extract timeless mathematical laws, breaks fown for inside observers. (Smolins point in reality of time, evolution of law).

    IMO: So does inside observations take place? Of course! but they can only be described as an evolutionary process. Evolutionary models requires a different type of mathematics. The focus is more on algorithms and information processing, than on a set of rules the defines a flow in state space.

    /Fredrik
     
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