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B Quantum gravity question

  1. Oct 6, 2016 #1
    What is the second paragraph referring to in quantum gravity? specific name for it (like asymptotic gravity, etc.)..

    http://backreaction.blogspot.com/2016_09_01_archive.html

    "Just combining quantum field theory with general relativity doesn’t work because, as confirmed by countless experiments, all the particles we know have quantum properties. This means (among many other things) they are subject to Heisenberg’s uncertainty principle and can be in quantum superpositions. But they also carry energy and hence should create a gravitational field. In general relativity, however, the gravitational field can’t be in a quantum superposition, so it can’t be directly attached to the particles, as it should be.

    One can try to find a solution to this conundrum, for example by not directly coupling the energy (and related quantities like mass, pressure, momentum flux and so on) to gravity, but instead only coupling the average value, which behaves more like a classical field. This solves one problem, but creates a new one. The average value of a quantum state must be updated upon measurement. This measurement postulate is a non-local prescription and general relativity can’t deal with it – after all Einstein invented general relativity to get rid of the non-locality of Newtonian gravity. (Neither decoherence nor many worlds remove the problem, you still have to update the probabilities, somehow, somewhere.)"
     
  2. jcsd
  3. Oct 6, 2016 #2

    ShayanJ

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    SemiClassical gravity, which is not a way of quantizing gravity!
    It means coupling quantum matter to classical gravity as explained by Sabine.
     
  4. Oct 18, 2016 #3

    naima

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    There are superpositions in quantum gravity.
     
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