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In previous works, we showed that both time and space can emerge from entanglement within a globally constrained quantum Universe, with no background coordinates. By extending the Page and Wootters quantum time formalism to include both…

General Relativity and Quantum Cosmology · Physics 2025-09-30 Tommaso Favalli

Attempts to formulate a quantum theory of gravitation are collectively known as {\it quantum gravity}. Various approaches to quantum gravity such as string theory and loop quantum gravity, as well as black hole physics and doubly special…

High Energy Physics - Theory · Physics 2011-12-25 Ahmed Farag Ali , Saurya Das , Elias C. Vagenas

Many-particle entanglement is a fundamental concept of quantum physics that still presents conceptual challenges. While spin-squeezed and other nonclassical states of atomic ensembles were used to enhance measurement precision in quantum…

Quantum Physics · Physics 2018-11-09 Matteo Fadel , Tilman Zibold , Boris Décamps , Philipp Treutlein

We define and study kinematical observables involving fermion spin, such as the total spin of a collection of particles, in loop quantum gravity. Due to the requirement of gauge invariance, the relevant quantum states contain strong…

General Relativity and Quantum Cosmology · Physics 2021-04-07 Refik Mansuroglu , Hanno Sahlmann

This paper is a serious attempt at reconciling quantum and classical mechanics through the concept of dynamic space and the acceptance of non-zero Ricci tensor for vacuum. Starting with scalar particles, the paper shows that with those two…

General Physics · Physics 2007-05-23 Jose B. Almeida

I. The arena of quantum mechanics and quantum field theory is the abstract, unobserved and unobservable, M-dimensional formal Hilbert space [not equal to] spacetime. II. The arena of observations and, more generally, of all events (i.e.…

General Physics · Physics 2023-10-05 Johan Hansson

We review recent literature on the connection between quantum entanglement and cosmology, with an emphasis on the context of expanding universes. We discuss recent theoretical results reporting on the production of entanglement in quantum…

General Relativity and Quantum Cosmology · Physics 2015-03-20 Eduardo Martin-Martinez , Nicolas C. Menicucci

In a quantum gravity theory the entropy of entanglement $S$ between the fundamental degrees of freedom spatially divided by a surface is discussed. The classical gravity is considered as an emergent phenomenon and arguments are presented…

High Energy Physics - Theory · Physics 2008-11-26 Dmitri V. Fursaev

Central to the development of any new theory is the investigation of the observable consequences of the theory. In the search for quantum gravity, research in phenomenology has been dominated by models violating Lorentz invariance (LI) --…

General Relativity and Quantum Cosmology · Physics 2010-09-09 Lydia Philpott

It is shown that, with some reasonable assumptions, the theory of general relativity can be made compatible with quantum mechanics by using the field equations of general relativity to construct a Robertson-Walker metric for a quantum…

High Energy Physics - Theory · Physics 2007-05-23 Vu B Ho

A satisfactory theory of quantum gravity may necessitate a drastic modification of our perception of space-time, by giving it a foamy structure at distances comparable to the Planck length. It is argued in this essay that the experimental…

General Relativity and Quantum Cosmology · Physics 2009-09-11 John. Ellis , N. E. Mavromatos , D. V. Nanopoulos

We postulate that consciousness is intrinsically connected to quantum spin since the latter is the origin of quantum effects in both Bohm and Hestenes quantum formulisms and a fundamental quantum process associated with the structure of…

Quantum Physics · Physics 2007-11-08 Huping Hu , Maoxin Wu

The interface between quantum theory and gravity represents still uncharted territory. Recently, some works suggested promising alternative approaches aimed at witnessing quantum features to test the fundamental nature of gravity in…

Quantum Physics · Physics 2025-04-08 Marta Maria Marchese , Martin Plávala , Matthias Kleinmann , Stefan Nimmrichter

We consider two interacting systems when one is treated classically while the other system remains quantum. Consistent dynamics of this coupling has been shown to exist, and explored in the context of treating space-time classically. Here,…

Quantum Physics · Physics 2023-12-07 Jonathan Oppenheim , Carlo Sparaciari , Barbara Šoda , Zachary Weller-Davies

In relativistic quantum mechanics, elementary particles are described by irreducible unitary representations of the Poincare group. The same applies to the center-of-mass kinematics of a multi-particle system that is not subject to external…

General Physics · Physics 2013-03-22 Walter Smilga

We have studied a relativistically covariant Stern-Gerlach (SG) experiment for a relativistic spin and a Dirac spin. We have obtained the relativistic spin in an arbitrary frame by using the classical spin dipole tensor, which gives the…

Quantum Physics · Physics 2013-10-04 Taeseung Choi , Yeong Deok Han

It is a general belief that all fundamental interactions need to be quantized. However, all attempts to develop a quantum theory of gravity presented various problems, leading to a recent active debate about how to probe its quantum nature.…

Quantum Physics · Physics 2018-06-25 Salvatore M. Giampaolo , Tommaso Macrì

Theories of quantum gravity generically presuppose or predict that the reality underlying relativistic spacetimes they are describing is significantly non-spatiotemporal. On pain of empirical incoherence, approaches to quantum gravity must…

History and Philosophy of Physics · Physics 2018-05-03 Vincent Lam , Christian Wuthrich

The theories of quantum mechanics and relativity dramatically altered our understanding of the universe ushering in the era of modern physics. Quantum theory deals with objects probabilistically at small scales, whereas relativity deals…

General Physics · Physics 2021-04-13 John Skilling , Kevin H. Knuth

We discuss some fundamental issues underlying gravitational physics and point out some of the main shortcomings of Einstein's General Relativity. In particular, after taking into account the role of the two main objects of relativistic…

General Relativity and Quantum Cosmology · Physics 2014-09-12 S. Capozziello , G. Lambiase