T Padmanabhan 2002 Class. Quantum Grav. 19 L167 doi:10.1088/0264-9381/19/17/102
Why do we observe a small but nonzero cosmological constant?
FREE ARTICLET Padmanabhan
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The current observations seem to suggest that the universe has a positive cosmological constant of the order of H20 while the most natural value for the cosmological constant will be L−2P, where LP = (G
/c3)1/2 is the Planck length. This reduction of the cosmological constant from L−2P to L−2P(LPH0)2 may be interpreted as due to the ability of quantum microstructure of spacetime to readjust itself and absorb bulk vacuum energy densities. Being a quantum-mechanical process, such a cancellation cannot be exact and the residual quantum fluctuations appear as the 'small' cosmological constant. I describe the features of a toy model for the spacetime microstructure which could allow for the bulk vacuum energy densities to be cancelled leaving behind a small residual value of the correct magnitude. Some other models (such as those based on the canonical ensemble for the 4-volume or quantum fluctuations of the horizon size) lead to an insignificantly small value of H20(LPH0)n with n = 0.5–1 showing that obtaining the correct order of magnitude for the residual fluctuations in the cosmological constant is a nontrivial task, because of the existence of the small dimensionless number H0LP.
- PACS
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98.80.Jk Mathematical and relativistic aspects of cosmology
04.20.Gz Spacetime topology, causal structure, spinor structure
- MSC
- Subjects
- Dates
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Issue 17 (7 September 2002)
Received 16 July 2002
Published 16 August 2002
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Why do we observe a small but nonzero cosmological constant?
T Padmanabhan 2002 Class. Quantum Grav. 19 L167
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