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

1. Feb 1, 2007

### josh1

Specifically what Im 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.

2. Feb 1, 2007

### rtharbaugh1

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

3. Feb 2, 2007

### josh1

Im 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.

4. Feb 2, 2007

### Demystifier

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.

Last edited: Feb 2, 2007
5. Feb 2, 2007

### coalquay404

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.

Last edited: Feb 2, 2007
6. Feb 2, 2007

### Thomas Larsson

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.

7. Feb 2, 2007

### coalquay404

Ack! Apologies, it was early morning here and I hadn't had coffee. Fixed now.

8. Feb 2, 2007

### rtharbaugh1

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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