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Algebraic Observational Cosmology
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What can be measured by an observer in our universe? We address this question by constructing an algebra of gravitationally-dressed observables accessible to a comoving observer in FLRW spacetimes that are asymptotically de Sitter in the past, describing an inflationary epoch. An essential quantized degree of freedom is the zero-mode of the inflaton, which leads to fluctuations in the effective cosmological constant during inflation and prevents the existence of a maximum entropy state in the semiclassical limit. Due to the inaccessibility of measurements beyond our cosmological horizon, we demonstrate that all states are mixed with well-defined von Neumann entropy (up to a state-independent constant). For semiclassical states, the von Neumann entropy corresponds to the generalized entropy of the observer's causal diamond, a fine-grained quantity that is sensitive to the initial conditions of the universe.
Forward citations
Cited by 9 Pith papers
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Uniqueness of null-local modular flow
For the free massless scalar in a Minkowski causal diamond, the vacuum is the unique state or weight in the vacuum sector whose modular flow is local on the null boundary.
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A de Sitter Anti-Scrambling Algebra
In a toy model of de Sitter quantum gravity, shockwave time advances break the KMS condition and prevent the Hartle-Hawking state from being a trace on the observer's crossed-product algebra.
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Algebras for generalized entanglement wedges
Generalized (Bousso–Penington) entanglement wedges are conjectured to carry von Neumann algebras such that S_gen(W) = S(ω|A_W) − log Ind(E) + K_Ω (eq. 2.7), making BP's monotonicity and strong subadditivity consequenc...
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Limits on the Statistical Description of Charged de Sitter Black Holes
For charged de Sitter black holes, choosing the Bousso-Hawking observer normalization keeps the heat capacity finite in the Nariai limit, removing the expected log-T breakdown except in the cold and ultracold limits.
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Observers, local measurements, and topology
Measurement correlations along an observer's worldline define a simplicial complex whose homology is proposed to be the topology of the accessible quantum-gravitational spacetime.
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Stochastic inflation as an open quantum system
Stochastic inflation emerges from an open-quantum-system derivation, with a Lindblad master equation that reduces to and corrects Starobinsky's Fokker-Planck equation.
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Algebras, Entanglement Islands, and Observers
Entanglement islands in the AdS/bath island model realize the quantum-gravity 'observer' as a Goldstone vector mode, making the island operator algebra an emergent Type II∞ von Neumann algebra.
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Black hole thermodynamics at null infinity. Part 1: Dual Generalized Second Law
At future null infinity, the generalized second law for a Schwarzschild black hole becomes the monotonic decrease of a free energy, or grand potential, constructed from the Bondi mass and angular-mode chemical potentials.
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Quantum gravity observables: observation, algebras, and mathematical structure
A perspective arguing that gravitationally dressed observables generalize crossed product algebras and that quantum gravity may need non-algebraic structure on Hilbert space.
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