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Why Boltzmann Brains Don't Fluctuate Into Existence From the De Sitter Vacuum

Boddy, Kimberly K. and Carroll, Sean M. and Pollack, Jason (2015) Why Boltzmann Brains Don't Fluctuate Into Existence From the De Sitter Vacuum. . (Submitted)

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Many modern cosmological scenarios feature large volumes of spacetime in a de Sitter vacuum phase. Such models are said to be faced with a "Boltzmann Brain problem" - the overwhelming majority of observers with fixed local conditions are random fluctuations in the de Sitter vacuum, rather than arising via thermodynamically sensible evolution from a low-entropy past. We argue that this worry can be straightforwardly avoided in the Many-Worlds (Everett) approach to quantum mechanics, as long as the underlying Hilbert space is infinite-dimensional. In that case, de Sitter settles into a truly stationary quantum vacuum state. While there would be a nonzero probability for observing Boltzmann-Brain-like fluctuations in such a state, "observation" refers to a specific kind of dynamical process that does not occur in the vacuum (which is, after all, time-independent). Observers are necessarily out-of-equilibrium physical systems, which are absent in the vacuum. Hence, the fact that projection operators corresponding to states with observers in them do not annihilate the vacuum does not imply that such observers actually come into existence. The Boltzmann Brain problem is therefore much less generic than has been supposed.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Boddy, Kimberly K.0000-0003-1928-4667
Carroll, Sean M.0000-0002-4226-5758
Pollack, Jason0000-0003-4754-4905
Additional Information:SMC would like to thank the organizers of the Philosophy of Cosmology workshop in Tenerife – Joe Silk, Simon Saunders, Khalil Chamcham, John Barrow, Barry Loewer, and David Albert – for putting together such a unique and stimulating meeting. We are grateful to Jim Hartle, Seth Lloyd, and Mark Srednicki for conversations on the issues discussed in Section IV. This research is funded in part by the Walter Burke Institute for Theoretical Physics at Caltech, by DOE grant DE-SC0011632, and by the Gordon and Betty Moore Foundation through Grant 776 to the Caltech Moore Center for Theoretical Cosmology and Physics.
Group:Walter Burke Institute for Theoretical Physics, Moore Center for Theoretical Cosmology and Physics
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Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Department of Energy (DOE)DE-SC0011632
Gordon and Betty Moore Foundation776
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Record Number:CaltechAUTHORS:20150814-091340697
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59529
Deposited By: Joy Painter
Deposited On:14 Aug 2015 16:22
Last Modified:02 Jun 2023 00:22

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