’t Hooft on the Foundations of Superstring Theory

[Demystifier]

But the need to gauge-fix in Bohmian gravity (the shift and lapse functions) seems a far more important difficulty, anyway.

Yes, I definitely agree with that.

 

[atyy]

But the need to gauge-fix in Bohmian gravity (the shift and lapse functions) seems a far more important difficulty, anyway.

Yes, I definitely agree with that.

Why? If the initial condition problem is solved, then just apply Bohmian mechanics to QFT and get quantum gravity by AdS/CFT.

 

[Demystifier]

Why? If the initial condition problem is solved, then just apply Bohmian mechanics to QFT and get quantum gravity by AdS/CFT.

You cannot get gravity by AdS/CFT if QFT of interest is not conformal, and if the gravitational background is not AdS. Which, in the world in which we live, is not.

 

[atyy]

You cannot get gravity by AdS/CFT if QFT of interest is not conformal, and if the gravitational background is not AdS. Which, in the world in which we live, is not.

Yes, no realistic cosmologies yet. But I think it's been extended to non-CFTs, eg. section 1.3.3 of http://arxiv.org/abs/gr-qc/0602037 .

 

[Demystifier]

Yes, no realistic cosmologies yet. But I think it's been extended to non-CFTs, eg. section 1.3.3 of http://arxiv.org/abs/gr-qc/0602037 .

The evidence for general gauge/gravity duality is still rather poor. Most evidence on it (e.g., in QCD) suggests that, at best, it is only an approximation.

 

[atyy]

The evidence for general gauge/gravity duality is still rather poor. Most evidence on it (e.g., in QCD) suggests that, at best, it is only an approximation.

According to http://particle.physics.ucdavis.edu/blog/?p=240 , that case is weak coupling and small N. So it doesn't contradict that one can have the duality for non-CFTs that are strongly coupled with large N.

 

[atyy]

While there are some uncertainties regarding how statistical mechanics arises from classical mechanics, I think those uncertainties are not very serious. Anyway, the situation is very similar with Bohmian mechanics.

Do you agree with a sentiment such as "in the context of inflationary cosmology, that corrections to the Born rule in the early universe would in general have potentially observable consequences for the cosmic microwave background (CMB). This is because, according to inflationary theory, the primordial perturbations that are currently imprinted on the CMB were generated at early times by quantum vacuum fluctuations whose spectrum is conventionally determined by the Born rule." http://arxiv.org/abs/1103.1589

Is the proof of deviations from QM part of what you consider almost certainly part of Bohmian mechanics applied to cosmology?

 

[Demystifier]

Do you agree with a sentiment such as "in the context of inflationary cosmology, that corrections to the Born rule in the early universe would in general have potentially observable consequences for the cosmic microwave background (CMB). This is because, according to inflationary theory, the primordial perturbations that are currently imprinted on the CMB were generated at early times by quantum vacuum fluctuations whose spectrum is conventionally determined by the Born rule." http://arxiv.org/abs/1103.1589

Is the proof of deviations from QM part of what you consider almost certainly part of Bohmian mechanics applied to cosmology?

I think it is a possibility, but not an almost certain one.

 

[Demystifier]

So it doesn't contradict that one can have the duality for non-CFTs that are strongly coupled with large N.

I guess it means that gauge/gravity duality is exact only in the limit of infinite coupling and N, while in all other cases it is still an approximation. Do I need to stress that realistic coupling and N are not very close to infinite (even if they are both larger than 1)?

 

[atyy]

I think it is a possibility, but not an almost certain one.

Would you agree that it's almost certain that BM predicts deviations from QM at some level?

 

[Demystifier]

Would you agree that it's almost certain that BM predicts deviations from QM at some level?

Yes. The question is - is it possible to access that level by measurements?

 

[atyy]

Yes. The question is - is it possible to access that level by measurements?

That's very interesting (although maybe not practical to measure). So a discussion of BM really does belong in BTSM:)

 

[tom.stoer]

I guess it means that gauge/gravity duality is exact only in the limit of infinite coupling and N, while in all other cases it is still an approximation. Do I need to stress that realistic coupling and N are not very close to infinite (even if they are both larger than 1)?

I think approximate gauge/gravity duality and approximate dualities in string theories may indicate that S(QCD) is not the low energy limit of some string-like theory, but that string theory may be an approximation to S(QCD) in a certain limit. First time in physics that we spent 10 times more mony in defining the approximation than in solving the fundamental theory ;-)

 

[Demystifier]

That's very interesting (although maybe not practical to measure). So a discussion of BM really does belong in BTSM:)

I agree.