A positive cosmological constant * SUSY/string theory

  • Thread starter bananan
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lee smolin claims that SUSY/string theory can account for negative (anti-DS) and zero cosmological constant, but not a positive de-sitter constant, which is what has been observed.

he also claims the kodama state in LQG has a good semiclassical limit that is GR, and incorporates a small positive CC, and that witten's paper on kodama-chern is not entirely applicable.

what's the current research on these claims?
 
Witten discusses this in http://www.arxiv.org/abs/hep-th/0106109 . The problem seems to be that a holographic quantum description is impossible in de Sitter space, because it lacks the correct kind of asymtopia to put the holographic data on. On can perhaps avoid this problem by making the counterfactual assumption that the universe is really AdS, and we live in a metastable dS bubble inside the AdS universe.
 

marcus

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Thomas Larsson said:
Witten discusses this in http://www.arxiv.org/abs/hep-th/0106109 . The problem seems to be that a holographic quantum description is impossible in de Sitter space, because it lacks the correct kind of asymtopia to put the holographic data on. On can perhaps avoid this problem by making the counterfactual assumption that the universe is really AdS, and we live in a metastable dS bubble inside the AdS universe.
Thanks for spotlighting this paper. For my own and others' convenience, I'll copy the abstract here. It seems to fit nicely with your interpretation.

http://www.arxiv.org/abs/hep-th/0106109
Quantum Gravity In De Sitter Space
Edward Witten
19pp

"We discuss some general properties of quantum gravity in De Sitter space. It has been argued that the Hilbert space is of finite dimension. This suggests a macroscopic argument that General Relativity cannot be quantized -- unless it is embedded in a more precise theory that determines the value of the cosmological constant. We give a definition of the quantum Hilbert space using the asymptotic behavior in the past and future, without requiring detailed microscopic knowledge. We discuss the difficulties in defining any precisely calculable or measurable observables in an asymptotically de Sitter spacetime, and explore some meta-observables that appear to make mathematical sense but cannot be measured by an observer who lives in the spacetime. This article is an expanded version of a lecture at Strings 2001 in Mumbai."
 

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