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[2501.02359] Quantum mechanics and observers for gravity in a closed universe

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Abstract:Recent arguments based on the quantum extremal surface formula or the gravitational path integral have given fairly compelling evidence that the Hilbert space of quantum gravity in a closed universe is one-dimensional and real. How can this be consistent with the complexity of our own experiences? In this paper we propose that the experiences of any observer $Ob$ in a closed universe can be approximately described by a quantum mechanical theory with a Hilbert space whose dimension is roughly $e^{S_{Ob}}$, where $S_{Ob}$ is the number of degrees of freedom of $Ob$. Moreover we argue that the errors in this description are exponentially small in $S_{Ob}$. We give evidence for this proposal using the gravitational path integral and the coding interpretation of holography, and we explain how similar effects arise in black hole physics in appropriate circumstances.

[2501.02359] Quantum mechanics and observers for gravity in a closed universe Skip to main content arXiv is now an independent nonprofit! Learn more × Search arXiv Press Enter to search · Advanced search --> High Energy Physics - Theory arXiv:2501.02359 (hep-th) [Submitted on 4 Jan 2025 ( v1 ), last revised 17 Jan 2025 (this version, v2)] Title: Quantum mechanics and observers for gravity in a closed universe Authors: Daniel Harlow , Mykhaylo Usatyuk , Ying Zhao View a PDF of the paper titled Quantum mechanics and observers for gravity in a closed universe, by Daniel Harlow and 2

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