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Loop and central cosmo mingle (Cornish glimpses Gambini)

  1. Nov 19, 2008 #1


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    This item has connections with the definition of time, the unresolved black hole information paradox, the interpretation of quantum mechanics involving real physical clocks, loop quantum gravity, conventional mainstream cosmology. It's a small news item, in a way, perhaps just a straw in the wind---but interesting because of the many cross-field ties.

    Neil Cornish is an important figure in conventional mainstream cosmology. He used to have a pet monkey*. He has co-authored a bunch with Princeton's David Spergel including some of the main WMAP reports. He's more than usually creative idea-wise, by mainstream cosmo standards, IMHO. We've discussed several of his papers here at PF. Like the "circles in the sky" one that derived a minimum size for presentday space, and constrained the topology. He does stuff that surprise you but turn out to be mathematically and observationally very solid. Edgey but not flakey. Just the sort of research you want to make a field go.

    Now he is on to something that a prominent LQG guy, Rodolfo Gambini, has also been working on. This means that the 2005-2007 papers of Gambini, Pullin, and Porto are authomatically more visible. These show that if you drop the idea of a perfect classic clock (basic to conventional QM) and re-formulate QM just using realistic physical clocks**, then there is a gradual rate of natural information loss and certain puzzles are resolved.

    One of the GPP authors has actually posted some on PF, and we have discussed the GPP papers some, in past years. Despite their intrinsic interest, they haven't gotten as much notice as they deserve. I can't guess why: perhaps partly because Gambini is based in Montevideo and possibly also because he belongs to the Loop research community.

    Anyway now we have a sign of some research confluence. Cornish cites 3 of the GPP papers and offers a different way of proving a result similar to theirs. Quite possibly an improvement. Here's the paper:

    Semi-classical limit and minimum decoherence in the Conditional Probability Interpretation of Quantum Mechanics
    Vincent Corbin, Neil J. Cornish
    8 pages
    (Submitted on 17 Nov 2008)

    "The Conditional Probability Interpretation of Quantum Mechanics replaces the abstract notion of time used in standard Quantum Mechanics by the time that can be read off from a physical clock. The use of physical clocks leads to apparent non-unitary and decoherence. Here we show that a close approximation to standard Quantum Mechanics can be recovered from conditional Quantum Mechanics for semi-classical clocks, and we use these clocks to compute the minimum decoherence predicted by the Conditional Probability Interpretation."

    **very much as Carlo Rovelli does, actually. In his book Quantum Gravity (2004) and also in his FQXi contest essay on What is Time?
    Intriguing to see these lines of thought come together.

    *back in 2005, if you went to Cornish' webpage, he had a picture of himself with this rather large cinnamon-colored monkey sitting on his shoulder, both of them grinning at the camera.
    Last edited: Nov 19, 2008
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