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The Landscape?

  1. Jul 24, 2004 #1
    If we had consider the energy in any system, how would this look if we put the proverbial glasses on, that only lets us see energy. What would this landscape look like, if we had a string perspective and an LQG perspective?

    These would have to be geometrically considered, when spoken at the quantum level.
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  3. Jul 24, 2004 #2


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    Because of the Boltzman reference in your link, I conjecture you are talking about thermodynamics and statistical mechanics here when you say energy. Am I right?

    Both quantum gravity and string theory address the important issues of theormodynamics, and the one place where they can be compared is in the thermodynamics of black holes, as originally developed by Hawking and Beckenstein. We have had prior discussions of this, but for convenience I will sketch the basics results.

    String theory does basic first principles calculations and gets the correct answer. The only caveat is that they can only do this on black holes that have evaporated down to string dimensions. But granted that, their development is a triumph.

    Quantum Gravity also does a basic development; in their case it involves counting the edges of the quantum foam of spacetime that pierce the event horizon. In order to take away a quantum of radiation from the black hole in QG, such a piercing must happen. In the original calculation they got an answer that was proportional to the correct one, with an undetermined constant in it called the Immirzi parameter. If they could calculate a value of the Immirzi parameter from their theory they would be done. For the last couple of years various QG physicists have been suggesting one thing and another to try and settle this issue. Some of these attempts were hopeful, but then got shot down. Others remain out there being evaluated. It is fair to say the problem has not been settled as of July 2004.
    Last edited: Jul 24, 2004
  4. Jul 24, 2004 #3


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    I share that assessment. The Immirzi number has proven difficult to pin down: it is like a fly that always gets out of the way when you swat at it.
    As of July 2004 you could have said things got a little less settled! in a paper posted 14July Christoph Meissner recalculated and found a value of 0.2375, roughly twice as big as the 0.1274 found in the 1990s by Ashtekar et al.

    selfAdjoint, could you explain some more what the restrictions in the String theory result are, at present. Has the requirement of extremality been lifted to the theorists' satisfaction? Are there some extra side-assumptions we should be aware of? If not too difficult to explain, could you say how does it come about that one needs the hole to have evaporated down to string dimensions? I can count on your fairness and lack of bias about this which means that what you say is especially helpful to me. Is there a recent survey paper that sums up the current state of this?
    Last edited: Jul 24, 2004
  5. Jul 24, 2004 #4


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    According to this paper

    as of last December they hadn't. But check out the last part where they try to show that supermassive strings can change into black holes - smoothly!

    In my Zwiebach book, chapter 16 discusses how they do the extremal black hole (this is, he says , the simplest example) in 5 dimensions. They start in supersymmetric type IIB superstring theory and compact five of its 10 dimensions on tiny circles. This leaves a 5 dimensional Minkowski space uncompacted and the black hole sits in it. The theory assumes zero string coupling constant, but the supersymmetry will preserve the physical effects calculated with zero coupling even at finite coupling, which is a main reason for choosing this particular configuration.

    They wrap D1 and D5 branes around the compacted circles in a particular way, these branes, being compacted, look to an observer in the 5-space like points. They are to be placed at the center of the black hole. This will reproduce the physical properties of the black hole (I left out some byplay with charges), but they do it in only one way, and the point of the excercise is to count the many ways of building the black hole. The total momentum is an integer N, and what they have to do is to count the number of ways N can be partitioned into momenta from physical states.

    The key is that there are open strings between the branes, with their ends fixed on them. Zwiebach cites three facts about this configuration:

    (1) The D1/D5 brane system is a bound state. Strings between two D1 branes or two D5 branes become massive and idle and do not contribute to the count.
    (2) A string from a D1 brane to a D5 brane has an opposite string going the other way, and between them these two strings have eight modes: four bosonic and four fermionic.
    (3) The Q1 D1 branes can join to form a brane wrapped Q1 times around one of the compact circles and the Q5 D5 branes can join to wrap Q5 times around the whole compact space.

    According to (2) there are 4Q1Q5 ways to assign bosonic string states, and an equal number of sdifferent fermionic state. But according to (3) the string endpoints can be assigned to any of the wrapppings. With this extra fact included, the count partition count comes out correct.
    Last edited: Jul 24, 2004
  6. Jul 24, 2004 #5
    Yes of course;

    I appreciate it.

    Thank you for taking the time

    Because we talk about the nature of geometry it is well evident to me that there are correlations that go along side of this geometrical consideration or we could not have gone down this road. I included thermodynamics to demonstrate that I can see this in a number of ways.

    One thought that I had in regards to LQG was the Monte Carlo issue in regards to quantum gravity. The structure that can be built from this theoretical position held my perspective in regards to the thermodynamcal issues as well.

    Yet we see where such meaning given to quantum gravity could have indeed given a complex issue to consider in the energy plot considered in thisexample.

    Here too, strings at supersymmetrical states giving us to consider the smoothness of these dynamics events if we consider suoergravity in supermetrical points. We discussed this at one time. Consider then metric points and then the mathematical calculation to supergravity. Do you see this correlation?

    If energy can leak into dimensions, lets think of the colliders here, where has it gone? Some like a orderly universe, whether it be LQG or Strings

    Last edited by a moderator: Apr 21, 2017
  7. Jul 24, 2004 #6
    If the blackhole was to grow and the boundaries are growing, the temperature would actually be cool, compare too critical density of this information, once this has been reached. The schwarzchild radius would equal the energy expended through entrophy increase from the collapse of the blackhole?

    In reading self adjoint's post I went looking too.

    So what we had heard from Hawking would have been no different then what we are hearing here?

    Last edited by a moderator: Apr 21, 2017
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