14 citations · 15 across the 9 of their papers we have counts for
12 papers
Toward a Unique Filter for the Gravitational Path Integral
Marc S. Klinger
In recent work, McNamara and Wang demonstrated that the failure of factorization for a gravitational path integral (GPI) can be understood as an incompleteness of its spectrum of s…
How to have your wormholes and factorize, too
Marc S. Klinger
We review three well known inconsistencies in the standard mathematical formulation of semiclassical gravity: the factorization problem, the information problem, and the closed uni…
A Theory of Backgrounds and Background Independence
Marc Klinger
In this note, we describe how the study of backgrounds for general quantum systems can be formulated in terms of the representation theory of abstract algebras. We illustrate…
Generalized Entropy is von Neumann Entropy II: The complete symmetry group and edge modes
Marc S. Klinger, Jonah Kudler-Flam, Gautam Satishchandran
We consider the algebra of observables of perturbative quantum gravity in the exterior of a stationary black hole or the static patch of de Sitter spacetime. It was previously argu…
The Many Faces of Non-invertible Symmetries
Shadi Ali Ahmad, Marc S. Klinger, Yifan Wang
We investigate the interplay between algebraic and categorical notions of non-invertible symmetries. In particular, a fusion categorical symmetry is shown to induce a…
The Problem of Time and its Quantum Resolution
Marc S. Klinger, Robert G. Leigh
In this essay, we argue that the problem of time should not be regarded as an issue to be resolved within the prevailing framework for studying quantum gravity, but rather as an in…
Extensions from within
Shadi Ali Ahmad, Marc S. Klinger
Inclusions and extensions lie at the heart of physics and mathematics. The most relevant kind of inclusion in quantum systems is that of a von Neumann subalgebra, which is the focu…
Emergent Geometry from Quantum Probability
Shadi Ali Ahmad, Marc S. Klinger
Carrying the insights of conditional probability to the quantum realm is notoriously difficult due to the non-commutative nature of quantum observables. Nevertheless, conditional e…
Relational Quantum Geometry
Shadi Ali Ahmad, Wissam Chemissany, Marc S. Klinger +1
A common feature of the extended phase space of gauge theory, the crossed product of quantum theory, and quantum reference frames (QRFs) is the adjoining of degrees of freedom foll…
Semifinite von Neumann algebras in gauge theory and gravity
Shadi Ali Ahmad, Marc S. Klinger, Simon Lin
von Neumann algebras have been playing an increasingly important role in the context of gauge theories and gravity. The crossed product presents a natural method for implementing c…
Quantum Reference Frames from Top-Down Crossed Products
Shadi Ali Ahmad, Wissam Chemissany, Marc S. Klinger +1
All physical observations are made relative to a reference frame, which is a system in its own right. If the system of interest admits a group symmetry, the reference frame observi…
Crossed Products, Conditional Expectations and Constraint Quantization
Marc S. Klinger, Robert G. Leigh
Recent work has highlighted the importance of crossed products in correctly elucidating the operator algebraic approach to quantum field theories. In the gravitational context, the…