’t Hooft on the Foundations of Superstring Theory

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Discussion Overview

The discussion centers around Gerard 't Hooft's paper on the foundations of superstring theory, exploring its theoretical underpinnings and implications for quantum gravity. Participants examine the legitimacy of string theory's foundations, its relation to quantum mechanics, and the broader context of 't Hooft's contributions to the field.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants note that 't Hooft's paper highlights the shaky foundations of superstring theory, suggesting that this lack of solidity may contribute to its strength during development phases.
  • There is a discussion on whether string theory can derive the assumptions of the Born rule as partially derived by Zurek, with some expressing skepticism about string theory's ability to do so better than other quantum theories.
  • Participants mention that string theory has not yet addressed foundational issues related to quantum theory and gravity.
  • Some express frustration over the perceived lack of interest in 't Hooft's work, attributing it to the complexity of the issues at hand.
  • A participant references 't Hooft's related papers on cellular automata and their implications for quantum field theory, suggesting that these ideas may be difficult to grasp and warrant further explanation.
  • There is a mention of the acknowledgment of "M. Porter" in 't Hooft's paper, implying a connection that could provide additional insights into the discussion.

Areas of Agreement / Disagreement

Participants express a range of views regarding the foundations of string theory and its ability to address quantum mechanics. There is no consensus on the effectiveness of string theory in deriving the Born rule or on the overall interest in 't Hooft's work, indicating ongoing debate and uncertainty.

Contextual Notes

Some participants highlight the complexity of the topics discussed, which may contribute to the hesitance in engaging with 't Hooft's ideas. The discussion reflects a variety of interpretations and assumptions that remain unresolved.

  • #61
mitchell porter said:
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.
 
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  • #62
mitchell porter said:
But the need to gauge-fix in Bohmian gravity (the shift and lapse functions) seems a far more important difficulty, anyway.

Demystifier said:
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.
 
  • #63
atyy said:
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.
 
  • #64
Demystifier said:
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 .
 
  • #65
atyy said:
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.
 
  • #66
Demystifier said:
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.
 
  • #67
Demystifier said:
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?
 
  • #68
atyy said:
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.
 
  • #69
atyy said:
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)?
 
  • #70
Demystifier said:
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?
 
Last edited:
  • #71
atyy said:
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?
 
  • #72
Demystifier said:
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:)
 
  • #73
Demystifier said:
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 ;-)
 
  • #74
atyy said:
That's very interesting (although maybe not practical to measure). So a discussion of BM really does belong in BTSM:)
I agree. :smile:
 

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