Absolute entropy and the observer's no-boundary state
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arXiv
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| Main Authors: | , , |
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| Format: | Preprint |
| Published: |
2025
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| _version_ | 1866911170650177536 |
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| author | Blommaert, Andreas Kudler-Flam, Jonah Urbach, Erez Y. |
| author_facet | Blommaert, Andreas Kudler-Flam, Jonah Urbach, Erez Y. |
| contents | We investigate the no-boundary proposal for closed universes with an observer. We argue that the observer's no-boundary state is the identity operator on the physical Hilbert space, i.e., the maximum entropy state and show this explicitly in Jackiw-Teitelboim gravity. Geometrically, the no-boundary state is a bra-ket wormhole. Expectation values in the no-boundary state provide a trace for the observer's algebra, which allows one to define von Neumann entropy for observers in different universes as the relative entropy with respect to the no-boundary state. This result is consistent with all previously discussed cases of traces for invariantly defined regions. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2505_14771 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Absolute entropy and the observer's no-boundary state Blommaert, Andreas Kudler-Flam, Jonah Urbach, Erez Y. High Energy Physics - Theory General Relativity and Quantum Cosmology We investigate the no-boundary proposal for closed universes with an observer. We argue that the observer's no-boundary state is the identity operator on the physical Hilbert space, i.e., the maximum entropy state and show this explicitly in Jackiw-Teitelboim gravity. Geometrically, the no-boundary state is a bra-ket wormhole. Expectation values in the no-boundary state provide a trace for the observer's algebra, which allows one to define von Neumann entropy for observers in different universes as the relative entropy with respect to the no-boundary state. This result is consistent with all previously discussed cases of traces for invariantly defined regions. |
| title | Absolute entropy and the observer's no-boundary state |
| topic | High Energy Physics - Theory General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2505.14771 |