Was lqg assessed unfairly at KITP program in quantum nature of singularities?

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Discussion Overview

The discussion revolves around the assessment of loop quantum gravity (LQG) during a program at the Kavli Institute for Theoretical Physics (KITP), particularly focusing on criticisms of LQG and comparisons with string theory. Participants explore the clarity of theoretical foundations and the implications of recent presentations on tachyon condensation within string theory.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express concern over the characterization of LQG as fundamentally weak, questioning whether this was a constructive conclusion to the program.
  • Others argue that while LQG has promising aspects, it lacks a clear overall explication, similar to criticisms leveled at string theory.
  • A participant asserts that the physical foundations of LQG are more sound than those of string theory, particularly at the non-perturbative level.
  • Another participant counters that the non-perturbative aspects of string theory are significant and that perturbative string theory faces deep conceptual problems that may relate to unresolved issues in general relativity (GR).
  • Concerns are raised about the experimental discrepancies of both perturbative bosonic and superstring theories, suggesting that without addressing non-perturbative phenomena, string theory may be fundamentally flawed.
  • Discussion includes a reference to Dr. Horowitz's comments on tachyon condensation and its potential insights into perturbative aspects of string theory, prompting inquiries about the relevance of this topic to the overall discussion.

Areas of Agreement / Disagreement

Participants express differing views on the strengths and weaknesses of LQG compared to string theory, with no consensus reached on the validity of the criticisms or the clarity of the theories' foundations.

Contextual Notes

Participants note the complexity of the issues discussed, including the dependence on definitions of clarity and soundness in theoretical physics, as well as the unresolved nature of certain mathematical and conceptual challenges in both LQG and string theory.

josh1
Specifically what I`m referring to is the final discussion summing up the program in which the weakness of lqg was characterized explicitly as "the whole theory". Was this a constructive way to end the program? Perhaps some of you would rather ignore this.
 
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As I said in the original thread about this KITP mini-program, I think Dr. Horowitz was saying that the good parts are interesting, promising, and may be useful, but as a whole, the theory lacks an entire clear explication. Of course I do not speak for KITP in any capacity, but only for myself, and from my very limited understanding. Surely few could argue against the same lack of an entire clear explication as applied to String.

R
 
rtharbaugh1 said:
Surely few could argue against the same lack of an entire clear explication as applied to String.

I`m sorry, but rather than "few could argue", most know for a fact that the ideas that currently serve as the "physical" foundations of lqg are nowhere near as sound as the one`s for string theory. That was the point of the conclusion. As I said, perhaps some of you would rather ignore this.
 
josh1 said:
most know for a fact that the ideas that currently serve as the "physical" foundations of lqg are nowhere near as sound as the one`s for string theory.
Can you explain that?
I think that the physical foundations of string theory are much more vague than that of LQG, at least at the NON-perturbative level.
String theory has many remarkable features, but clear foundations at the nonperturbative level are not one of them.
On the other hand, the physical foundation for LQG is simply the Einstein (or Einstein-Cartan) equation of gravity.
 
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Demystifier said:
Can you explain that?
I think that the physical foundations of string theory are much more vague than that of LQG, at least at the NON-perturbative level.

I think that this is probably the crucial point. The non-perturbative aspects and successes of string theory are undeniable, but the perturbative component is still, in my opinion, not understood at all. The reason for this is possibly the same as the reasons for the outstanding problems in GR: examing string theory perturbatively quickly makes one run into very, very deep conceptual problems. I'm beginning to come around to the line of thinking that states that perturbative string theory *cannot* be fully understood until the conceptual difficulties in GR (specifically, the problem of time and the operator ordering ambiguities in attempts at canonical quantization) are resolved.

That said, if the remaining conceptual problems in GR are finally understood, one could speculate that this will contribute to the resolution of LQG one way or the other far sooner than string theory.
 
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coalquay404 said:
The perturbative aspects and successes of string theory are undeniable,

:confused:

Perturbative bosonic string theory predicts 26 flat dimensions and tachyons, in complete disagreement with experiments.

Perturbative superstring theory predicts 10 flat dimensions and unbroken supersymmetry, in complete disagreement with experiments.

coalquay404 said:
but the non-perturbative component is still, in my opinion, not understood at all

Compactification of dimensions and supersymmetry breaking are non-perturbative phenomena. Thus, without this non-perturbative component, string theory is simply wrong.
 
Thomas Larsson said:
:confused:

Perturbative bosonic string theory predicts 26 flat dimensions and tachyons, in complete disagreement with experiments.

Perturbative superstring theory predicts 10 flat dimensions and unbroken supersymmetry, in complete disagreement with experiments.



Compactification of dimensions and supersymmetry breaking are non-perturbative phenomena. Thus, without this non-perturbative component, string theory is simply wrong.

Ack! Apologies, it was early morning here and I hadn't had coffee. Fixed now.
 
coalquay404 said:
..but the perturbative component (of String Theory) is still, in my opinion, not understood at all. ...

Dr. Horowitz seemed to think that Eva Silverstein's presentation on tachyon condensation provided a peturbative insight. Do you include tachyon condensation in this opinion? I have been meaning to look into this myself, having been made curious by Dr. Hubner's question in the final discussion about whether evolution in spacetime can be made to stop without going through a singularity, and Dr. Horowitz' reply invoking Dr. Silverstein's talk.

Has anyone here listened to the talk, or otherwise have insight about this?

R
 

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