Criticism of LQG - What do we miss?

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SUMMARY

The forum discussion critically examines Loop Quantum Gravity (LQG), highlighting its reliance on SU(2)-colored graphs without clear dimensionality and questioning the justification for using SU(2) as the gauge group. Key issues include the treatment of the cosmological constant, the lack of consideration for multiple smooth structures in four-dimensional spacetime, and the implications of the asymptotic safety approach for renormalization. The conversation emphasizes the need for a more comprehensive understanding of the relationship between gravity and matter, as well as the potential for integrating concepts from quantum mechanics and relativity.

PREREQUISITES
  • Understanding of Loop Quantum Gravity (LQG) principles
  • Familiarity with SU(2) gauge theory
  • Knowledge of the asymptotic safety approach in quantum gravity
  • Basic concepts of smooth structures in four-dimensional spacetime
NEXT STEPS
  • Research the implications of the asymptotic safety approach for quantum gravity
  • Explore the role of smooth structures in four-dimensional spacetime
  • Investigate the relationship between LQG and the holographic principle
  • Study the latest review papers on LQG, particularly the one by Rovelli from 2010
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Physicists, researchers in quantum gravity, and students interested in the foundational aspects of LQG and its implications for understanding spacetime and matter.

  • #31
good point!
 
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  • #32
marcus said:
I think that is probably the reason that Ashtekar, who is longterm friends with Penrose and must have heard Penrose talk about entropy and bounce on countless occasions, has never seemed worried by Penrose's thermo objection. Admittedly this is not spelled out rigorously, but it's in the context of a novel situation and I find that, to me, intuitively it makes sense.

I have always thought it intuitive that gravity was driving entropy (and time itself really). It is very interesting to see this pointed out with respect to Ashtekar's perspective, especially the sign reversal for entropy itself when gravity's sign changes.

It also seemed to me that a bounce would "fix" entropy so I have favored that idea over a pure big bang. It certainly answers the question of why the universe got to be so ordered. It will be interesting to see if this idea holds up under observations over the next decade or so.

Thank you marcus.
 

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