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Gravity and the quantum.

  1. Nov 19, 2004 #1


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    Gravity and the quantum.
    Abhey ashtekar.
    A broad perspective on quantum gravity.
    I have not seen reference to this article, but maybe i missed some threads.
    its a good read for none pros anyway.
  2. jcsd
  3. Nov 19, 2004 #2


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    I agree. It is a good read. Clear and up-to-date. Not too long.
    And he spends time discussing the applications.

    For a physics-watcher there are some little details that distinguish this survey from earlier ones and are worth mentioning. Although they are just details. I'll make a separate post about them.
  4. Nov 19, 2004 #3


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    Every now and then Ashtekar produces a survey like this, an overview with his perspective on where things are going.
    BTW here's the link to the abstract:

    Besides being up-to-date----the latest Ashtekar overview---what is special about this one. what tell-tale straws in the wind can be noticed?

    1. first there is the context
    he is paired off against the string theorist Gary Horowitz
    in a special 2005 issue of the New Journal of Physics celebrating the
    100th anniversary of Einstein's 1905 papers

    the special issue (edited by Jorge Pullin) is called
    Space-time 100 Years Later
    Here is the URL for the New Journal of Physics:

    I suppose hardcopy of the centennial issue may reach the shelf
    at university libraries. It sounds like a book "Space-time a Hundred Years Later", and it might sell as a book. But the primary access is electronic.

    So there is a kind of parity in the presentation of String and Non-string
    approaches to Quantum Gravity and their different perspectives on what will replace the space and time of General Relativity.

    Here's a link to the Gary Horowitz survey of String that Abhay's is paired with in the centennial issue

    2. He emphasizes some work by Rodolfo Gambini (consistent discretizations) that has so-far not been noticed by LQG people so much.
    We had someone come here to PF called Edgar1813 who is involved in this consistent discretizations line of research and apparently knows Gambini.

    Abhay is sort of like the center player, or the "quarterback" and it is a good thing if he notices someone in a forward position or out on the end. this is only a vague analogy. Anyway I watch for how much notice Gambini, Pullin, Porto etc get in a concise official-stamp-of-approval survey paper.

    3. His reference [41] is to the Ambjorn Jurkiewicz Loll paper about their computer Monte Carlo simulations "Emergence of a 4D World..."
    To me it is extemely unclear how this simplicial modeling fits together with LQG. but he is including it in his vision of how non-string Quantum Gravity is developing.

    4. His references [49] and [50] are to two papers by himself and Bojowald which have not even been posted on the preprint Arxiv yet. they are about what there is instead of a singularity, in black holes, and the LQG picture of how black holes evaporate

    there was a strong emphasis on applications, which ultimately lead to observable phenomena. this fall at Ashtekar's institute IGPG there was a series of 3 talks about LQG phenomenology by Parampreet Singh.
    the effort is to derive little details about the CMBR---its spectrum of bumps and dips---which could be looked-for. I think Abhay is pushing hard for finding something testable.

    another indicator besides the perspective in this survey article you flagged is just the lineup of seminar talks at Penn State----what his IGPG colleagues and visitors and graduate students are giving talks about. Some of the talks are online but most unfortunately are not.
    In case anyone has not tried this before, here is the schedule of talks (select "this semester" from menu)
    Last edited: Nov 19, 2004
  5. Nov 19, 2004 #4
    In page 30, Ashtekar says that in Loop Quantum Cosmology, the Belinski-Khalatnikov-Lifschitz type chaotic behavior predicted by General Relativity disappears. I didn't knew that GR predicted this chaotic behavior, is great that LQC can eliminate some of the chaos in our lifes :smile:
  6. Nov 19, 2004 #5


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    Miguel, as you know I cant offer expertise here, however if the type is such that it has a singularity over a whole surface
    then the curvature could behave in a chaotic way, as one approaches the surface of singularity
    it could be going everywhere to infinity, but not in an organized march

    I would expect you to know more about this.

    did you happen to see the paper by Bojowald that had "Bianchi 9"
    in the title. there was a chaotic singularity and he was dealing with this
    and removing it by quantizing. I think it was Spring 2004

    As for our lives, it seems to get worse and worse. Democracy is dying in the US. the educational system is failing. people are getting less rational. Global capitalism (which could be beneficial if properly controlled) is more and more monstrous. It resembles the chaotic approach to a classical singularity.
    Idiocy, bellicosity, and corruption rule.
    Perhaps our historical scenario should be called "Bianchi IX"
  7. Nov 19, 2004 #6


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    The Bojowald paper is Martin Bojowald, Ghanashyam Date, and Golam Mortura Hossain, The Bianchi IX model in Loop Quantum Gravity, gr-qc/0404039.

    As for your conclusions about society, back in the 1930's a poet wrote "Fool and villain rule the state". Different times, different fools, different villains. My theory is that democracy is ALWAYS chaotic. All my life I have been living in "interesting times".
  8. Nov 19, 2004 #7


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    In the nightmare of the dark
    All the dogs of Europe bark,
    And the living nations wait,
    Each sequestered in its hate;

    Intellectual disgrace
    Stares from every human face,
    And the seas of pity lie
    Locked and frozen in each eye.

    Follow, poet, follow right
    To the bottom of the night,
    With your unconstraining voice
    Still persuade us to rejoice;

    With the farming of a verse
    Make a vineyard of the curse,
    Sing of human unsuccess
    In a rapture of distress;

    In the deserts of the heart
    Let the healing fountain start,
    In the prison of his days
    Teach the free man how to praise.

    ---Auden, around 1939
  9. Nov 20, 2004 #8


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    AMen. Poets are the unacknolwledged legislators of mankind. Or as I have often thought, ballistic galvanometers of the human condition.
  10. Nov 20, 2004 #9
    I remember some article somewhere in which was compared the behaviour of Ashtekar and Smolin. Ashtekar an example of order, and methodology. Smolin a quite disorderly person, with his room always a chaotic mess. But, both have made their contributions to science, Ashtekar with his new formulation of GR, and Smolin with the creation of LQG. So, beware! don't underrate chaos, it can also come positive things from it.
    Nevertheless, I prefer the style of Ashtekar. I was a bit like Smolin a years ago, but now I prefer to have my books and my notebooks in localized places, its much more quick to access to information if you need to.
    I looked the paper, but I'm not interested in Bianchi models, as they represent rotating universes, that is not the case of ours. Remarkable the great vocabulary associated with the name Kasner: Kasner epoch, Kasner evolution, Kasner axes, Kasner singularity, Kasner sphere,...
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