Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session M08: Quantum Gravity |
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Sponsoring Units: DGRAV Chair: Jorge Pullin, Louisiana State University Room: Symphony III - 2nd Floor |
Monday, April 17, 2023 10:45AM - 10:57AM |
M08.00001: Black Holes are Watching You Daine L Danielson, Gautam Satishchandran, Robert M Wald We show that if a massive (or charged) body is put in a quantum superposition of spatially separated states in the exterior of a black hole, the mere presence of the black hole will eventually destroy the coherence of the superposition. This occurs because, in effect, the long-range fields sourced by the body radiate soft gravitons/photons through the horizon, allowing the black hole to harvest "which path" information about the superposition. The electromagnetic decoherence arises only when the superposed particle carries electric charge. However, since all matter sources gravity, the quantum gravitational decoherence applies to all superpositions. We provide estimates of the decoherence time for such quantum superpositions. |
Monday, April 17, 2023 10:57AM - 11:09AM |
M08.00002: Horizons are Watching You Gautam Satishchandran, Daine L Danielson, Robert M Wald We show, quite generally, that if a massive (or charged) body is put in a quantum spatial superposition, the mere presence of a Killing horizon in its vicinity will eventually decohere the superposition. This occurs because, in effect, the long-range field of the body is registered on the Killing horizon which, we show, necessitates a flux of ``soft horizon gravitons/photons'' through the horizon. The Killing horizon thereby harvests ``which path'' information of quantum superpositions and will decohere any quantum superposition in a finite time. In particular, we fully analyze the case of uniformly accelerating superposition in flat spacetime. From the Rindler perspective, this superposition is decohered due to a flux of "soft gravitons/photons" through the Rindler horizon with negligible (Rindler) energy. We show that, from the inertial perspective, the decoherence is due to radiation of high-frequency gravitons/photons to null infinity. Furthermore, this decoherence is distinct from — and larger than — the decoherence resulting from the presence of Unruh radiation. We also analyze decoherence due to the presence of the cosmological horizon in de Sitter spacetime. We provide estimates of the decoherence time for such quantum superpositions in both the Rindler and cosmological cases. |
Monday, April 17, 2023 11:09AM - 11:21AM |
M08.00003: Path Sums for Propagators on Causal Sets Samuel A Shuman A major challenge in Causal Set research is that theories need only to match general relativity and quantum field theory in the appropriate limits. This means that there should be many different ways to calculate the scalar field propagator that match the known limits, but may give significantly different results on the small scale. In this work, we explore under what conditions a path sum will correspond to a scalar field propagator in such a way that it matches the known value in the continuum limit. A general solution for the path sum is found and is verified numerically in a specific case. |
Monday, April 17, 2023 11:21AM - 11:33AM |
M08.00004: Dynamics of Causal Sets and Discrete Variational Principles He Liu, Luca Bombelli The causal sets program is an approach to discrete quantum gravity. One core task is finding a way of evolving causal sets that leads to manifoldlike structures. This talk will begin with results of the classical sequential growth (CSG) dynamics. In a CSG process, elements are added one at a time, and the new element's past structure is determined by a sequence of parameters. I will show the properties of our simulated early ``universe'' based on the chain abundancy. The second part is our attempt to a discrete variation of action for causal sets in a sequential growth process in general. We apply the variation scheme on different types of dynamical processes, and will show some preliminary results. |
Monday, April 17, 2023 11:33AM - 11:45AM |
M08.00005: Quantization of the Simplest Grain of Space: Quantum Geometry, Picard-Fuchs Equations, and Perturbative/Non-Perturbative Relations Hal M Haggard, Santanu Antu, Charles F Doran Quantization of the geometrical observables of spacetime is a key feature of quantum gravity. However, the area spectrum stands alone as having a complete analytic treatment. Even for the simplest, tetrahedral grain of space, research on other observables, like the volume, usually proceeds either completely numerically or via strong approximations. We methods that allow you to find the spectrum of a tetrahedral grain of space to arbitrary orders in hbar. These results are achieved through complexification of the underlying dynamical system and provide an accessible introduction to Picard-Fuchs equations and to new methods in non-perturbative quantization. In particular, this application provides a novel example of the non-perturbative quantization of a modular geometry that is not of the kinetic-plus-potential form and exhibits several features of the quantization of a nonlinear system that will be of general interest. |
Monday, April 17, 2023 11:45AM - 11:57AM |
M08.00006: The WKB Wavefunctions of Simplicial Grains of Space Santanu Bosu B Antu, Hal M Haggard, Charles F Doran Quantization of space is a key theme in quantum gravity. Here, we discuss the dynamics, volume spectrum, and the wavefunctions of the simplest grain of space---a tetrahedron. We take a semiclassical approach to the problem, which gives a more intuitive perspective on the quantum nature of space. In particular, we apply some classical geometrical results and a Poisson structure on the phase space to derive the dynamics of a Euclidean tetrahedron, and then derive the WKB eigenfunctions of these Euclidean simplices (which are of the form exp(iS/h), where S is the action integral) and compare them with the standard results. The action integral on our phase space naturally gives rise to elliptic integrals, which hints towards a very rich mathematical structure in the problem. |
Monday, April 17, 2023 11:57AM - 12:09PM |
M08.00007: Investigations into the relationship between loop quantum gravity and string theory John Joseph J Marchetta, Gerald B Cleaver A direct description of quantum gravity, which limits to Einstein's gravity at low energies, is one of the biggest open problems in physics. Two most prominent approaches are string theory, which has the proper low energy perturbative limit but lacks a full non-perturbative quantum gravity formulation, and loop quantum gravity, which is a non-perturbative and background independent quantum theory of holonomies of Ashtekar connections but has yet to reproduce classical general relativity. Various string dualities indicate that different string theories are all unified in a non-perturbative way by a more fundamental M-theory. It turns out that a long wavelength action of topological M theory expressed in terms of three forms reduces to 4-dimensional self-dual loop quantum gravity. It is then enticing to conjecture a duality between loop quantum gravity and string theory, to which we summarize the progress in this direction along with future outlooks. |
Monday, April 17, 2023 12:09PM - 12:21PM |
M08.00008: Universal Invariant Schrödinger Equation and Physical Foundation of Quantum Mechanics Siavash H Sohrab Scale-invariant Schrödinger equation is derived from invariant Bernoulli equation for incompressible potential flow with quantum mechanics wave function defined as velocity potential of atomic peculiar velocity [1]. Implications of the theory to the resolution and modified interpretation of quantum mechanics problems, namely (1) Nature of wave function Y (2) Wave-particle duality (3) Entanglement (4) Double-slit (5) EPR and action-at-a-distance (6) Quantum-jump and Trajectory (7) Schrödinger cat problems are discussed. The results are shown to be in accordance with classical quantum gravity as dissipative deterministic dynamic system [2], de Broglie-Bohm pilot wave model of quantum mechanics [3]. Some implications of the model to quantum cosmology and perceptions of Everett regarding existence of multiverse are also examined. |
Monday, April 17, 2023 12:21PM - 12:33PM |
M08.00009: A Review of Casimir Supported Traversable Wormhole and Warp Drive Spacetimes Patrick M Brown, Gerald B Cleaver The idea of super-luminal travel has been explored ever since the laws of special and general relativity were proposed [Davis, Prog.Astronaut.Aeronaut. (2009)]. There are two primary classes of solutions to Einstein’s equations that produce super-luminal travel; traversable wormholes and warp drives. Traversable wormholes were first explored by Morris and Thorne [American Journal of Physics 56, 395 (1988)] under static and spherically symmetric conditions, but have since been expanded to more general solutions [Visser, Lorentzian Wormholes (1996)]. Warp drives were first proposed by Alcubierre [Class.Quant.Grav.11:L73-L77,1994] and then expanded on by others, in particular Natario [Class.Quant.Grav. 19 (2002)], Lobo [Fundam.Theor.Phys. 189 (2017)], and Van De Broek [Class.Quant.Grav. 16 (1999)]; but still remain a poorly understood class of solutions. |
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