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Open problems in LQG

  1. Dec 30, 2009 #1


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    We will get a chance to gauge the progress in LQG---how far along they are in dealing with the main outstanding problems. There will be a workshop at Zakopane in late February early March. But we need someone to help by relaying information.


    Thanks to Guedes for this link!

    Jerzy Lewandowski is one of the organizers. And four other great people.

    The topics statement is:

    "The dynamics of quantum space (the status of the quantum Hamiltonian constraint in LQG and the covariant implementation of the dynamics in spin foam models and group field theories).

    The semiclassical limit and the continuum approximation in loop quantum gravity and the recovering of classical General Relativity and of matter quantum field theory in such approximation.

    Quantum gravitational observables.

    The role of diffeomorphisms in quantum gravity, their nature and possible breaking at the Planck scale or in discrete contexts."
    Last edited: Dec 30, 2009
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  3. Dec 30, 2009 #2


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    These QG schools are becoming something of a tradition.
    The first one was at Zakopane in 2007, then the second was at Corfu 2009,
    now again the third will be at Zakopane again.


    The official name of the European agency funding the schools is "Quantum Geometry and Quantum Gravity", so one could try to be correct one and say QGQG school, instead of just QG school. Because gravity is geometry. So treating gravity in a quantum way means that one must have a quantum state of geometry. Sometimes they say "QG-squared" to make this explicit. Sometimes they reverse the order and say "Quantum Gravity and Quantum Geometry". Doesn't matter, it's all one thing.

    The list of participants for this third Euro QG school is impressive.
    Reads like a Who's Who. Everybody whose papers we've been paying attention to. And more.

    90 participants listed, and it's clear there are omissions (the full list would include for example Lewandowski and Okolow) so 90 is a low estimate.

    Michael Reisenberger, from the University of the Republic, Montevideo, is expected to be there. One of those who introduced the spinfoam idea back in 1990s
    Last edited: Dec 30, 2009
  4. Jan 5, 2010 #3
    Interesting, thanks. Are there plans to put lectures or notes from this online, do you know?

    Nitpicking, but something I can't help but notice... they list four "open problems", and the problems they mention are real and important. But something which I as far as I am aware is still very much an open problem in LQG, but doesn't seem to be part of any of their four things, is "how do you integrate matter into the theory?". (I am not saying it should have been on the program, it is just always interesting to me that question seems to be so low priority in LQG research.)

    The matter thing aside, do you think it would be accurate to call the four problems they outline the four biggest open problems in LQG?
    Last edited: Jan 5, 2010
  5. Jan 5, 2010 #4


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    When one is a PhD student (everybody knows this or can figure it out) one is looking for open problems that are manageable. So the interesting problems are ones that it is the right time to look at and probably some work is already being done on them, that one can read to get abreast and find the way in.

    Since the aim of a school like this is to bring advanced PhD students, plus some new postdocs, into the research, when they say "Open Problems"
    they do not mean to give a complete survey of all the possible problems and their relative long-term importance.

    They could instead mean "Some Open Problems which now is a good time to work on".

    I don't know if they have the intention or the resources to put the lectures on line. It could be very interesting and valuable to us. But maybe they spent all their money bringing the best lecturers and paying travel expenses for their big crowd of people.

    There will be more than 90 people in the school. We'll see.

    About a survey of what ultimately are the biggest problems. I can't say, but I'm inclined to agree with you about matter. I might guess
    1. testing.
    2. including matter.
    3. explaining why macro reality is 4D and how scale affects geometry
    4 explaining the small positive cosmological constant

    Haven't thought about it, might change my mind if I reflected some.
    I wouldn't necessarily put the Schools list of 4 at the top of the ultimate list. they are just problems that people there consider doable now and what they can give you an introduction to.
    Last edited: Jan 5, 2010
  6. Jan 5, 2010 #5
    Marcus, interesting, thank you.
  7. Jan 6, 2010 #6


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