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Algebras, Regions, and Observers
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In ordinary quantum field theory, one can define the algebra of observables in a given region in spacetime, but in the presence of gravity, it is expected that this notion ceases to be well-defined. A substitute that appears to make sense in the presence of gravity and that also is more operationally meaningful is to consider the algebra of observables along the timelike worldline of an observer. It is known that such an algebra can be defined in quantum field theory, and the timelike tube theorem of quantum field theory suggests that such an algebra is a good substitute for what in the absence of gravity is the algebra of a region. The static patch in de Sitter space is a concrete example in which it is useful to think in these terms and to explicitly incorporate an observer in the description.
Forward citations
Cited by 20 Pith papers
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Microcausality without Lorentz invariance
Microcausality in Lorentz-violating states is equivalent to specific analyticity and exponential boundedness of spatial Fourier transforms of commutators, with explicit EFT constraints.
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The Making of von Neumann Algebras from Bulk Focusing
A boundary region's infinite-N operator algebra is a von Neumann algebra exactly when its generalized causal wedge closes on the same region; null geodesic focusing is the bulk mechanism.
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Disjoint additivity and local quantum physics
Local quantum systems should obey disjoint additivity plus Haag duality, a combination that survives higher-form symmetries and fails for known nonlocal constructions.
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Cosmological pole-skipping, shock waves and quantum chaotic dynamics of de Sitter horizons
Pole-skipping in Schwarzschild-de Sitter predicts superluminal and imaginary butterfly velocities, confirmed by shock wave analysis, hinting at nonlocal and non-Hermitian dual dynamics.
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Geometric modular flows in 2d CFT and beyond
In 2d CFTs, every suitably regular Unruh flow on the Rindler wedge is the modular flow of a state obtained by a conformal unitary acting on the vacuum or thermal state, and local entropy and stress-tensor formulas follow.
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Symmetric Product Orbifold Universality and the Mirage of an Emergent Spacetime
Symmetric product orbifolds have large-N thermal correlators identical to BTZ, undercutting the claim that a type III1 von Neumann algebra implies a sharp emergent horizon.
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Dressed Subsystems in Classical Gravity
Internally dressed subsystems, whose boundaries are located by fields within the region, are exactly those whose observables close under Poisson brackets in generally covariant theories.
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Wavefunctions of AdS$_3$ Universes and $T\bar{T}$-deformed Torus Partition Functions
The paper's central claim of an invertible bulk-boundary transform for T-Tbar deformed torus partition functions is broken by an incorrect inverse kernel and a factor-of-pi normalization inconsistency.
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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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Flow-geometry microstates
Particle-insertion microstates in AdS2→dS2 flow geometries are counted via wormhole path integrals, giving a Hilbert-space dimension e^{2S_Flow} that matches Gibbons-Hawking; the purely-de Sitter spanning claim depend...
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Entanglement measures for causally connected subregions and holography
Timelike separated subregions admit a transition-operator entropy, a complexified RT surface, and a timelike entanglement wedge cross section that equals half the analytically continued reflected entropy in AdS3/CFT2.
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Symmetry, Symmetry Topological Field Theory and von Neumann Algebra
The symmetric-sector von Neumann algebra of a QFT violates additivity or Haag duality exactly when the Lagrangian algebra of its SymTFT contains operators beyond the identity, with a sharper criterion distinguishing t...
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Observers and Timekeepers: From the Page-Wootters Mechanism to the Gravitational Path Integral
Metric summation produces the problem of time, topology summation produces the one-dimensional Hilbert space, and a timekeeper path integral gives observer-dependent holography.
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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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Quantum mechanics and observers for gravity in a closed universe
An observer inside a closed universe gets an approximately standard quantum description on a Hilbert space of dimension about e^{their entropy}, accurate up to exponentially small errors.
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Cosmological perturbations meet Wheeler DeWitt
The semiclassical Wheeler-DeWitt wavefunction matches the perturbation-theory wavefunction of cosmology up to a specific phase and normalization, verified in exponential-potential and slow-roll mini-superspace models.
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Crossed products and quantum reference frames: on the observer-dependence of gravitational entropy
Gravitational subregion entropy is observer-dependent: different quantum clocks produce different von Neumann algebras and different entropy functionals for the same global state.
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Observer Time from Causality in Perturbative Quantum Gravity
A lightbulb-and-mirror protocol defines diffeomorphism-invariant elapsed proper time, and its leading quantum gravity correction makes the time a noncommuting quantum operator.
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A Dynamical Systems Framework for Reinforcement Learning Safety and Robustness Verification
The claimed RL safety verification framework is absent from the manuscript; the body text is an unrelated high-energy physics paper about de Sitter horizon chaos.
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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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