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I give a brief review of the recovery of semiclassical time from quantum gravity and discuss possible extrapolations of this concept to the full theory.

General Relativity and Quantum Cosmology · Physics 2007-05-23 C. Kiefer

The classical theory of gravity predicts its own demise -- singularities. We therefore attempt to quantize gravitation, and present here a new approach to the quantization of gravity wherein the concept of time is derived by imposing the…

General Relativity and Quantum Cosmology · Physics 2010-11-01 Arkady Kheyfets , Warner A. Miller

If the history of science has taught us anything, it's that persistence and creativity makes the once impossible possible. It has long been thought experimental tests of quantum gravity are impossible. But during the last decade, several…

Popular Physics · Physics 2014-11-20 Sabine Hossenfelder , Lee Smolin

It is argued that quantum gravity has an interpretation as a topological field theory provided a certain constraint from the path intergral measure is respected. The constraint forces us to couple gauge and matter fields to gravity for…

High Energy Physics - Theory · Physics 2009-10-30 Andrew Toon

`How do our ideas about quantum mechanics affect our understanding of spacetime?' This familiar question leads to quantum gravity. The complementary question is also important: `How do our ideas about spacetime affect our understanding of…

General Relativity and Quantum Cosmology · Physics 2009-11-11 James B. Hartle

Background independence is often emphasized as an important property of a quantum theory of gravity that takes seriously the geometrical nature of general relativity. In a background-independent formulation, quantum gravity should determine…

General Relativity and Quantum Cosmology · Physics 2021-08-27 Martin Bojowald

The problem of time in the quantization of gravity arises from the fact that time in Schroedinger's equation is a parameter. This sets time apart from the spatial coordinates, represented by operators in quantum mechanics (QM). Thus "time"…

General Relativity and Quantum Cosmology · Physics 2016-05-06 M. Bauer

The conceptual definition and understanding of the nature of time, both qualitatively and quantitatively is of the utmost difficulty and importance, and plays a fundamental role in physics. Physical systems seem to evolve in paths of…

General Relativity and Quantum Cosmology · Physics 2015-01-14 Francisco S. N. Lobo

We introduced with coauthors some years ago a solution to the problem of time in quantum gravity which consists in formulating the quantum theory in terms of real clocks. It combines Page and Wootters' relational proposal with Rovelli's…

General Relativity and Quantum Cosmology · Physics 2022-05-03 Rodolfo Gambini , Jorge Pullin

We discuss the relevance of quantum gravity to the frontier questions in high energy phenomenology: the problems of dark matter, dark energy, and vacuum selection as well as the problems of emergent spacetime and wormholes. Dark matter and…

Basis and limitations of singularity theorems for Gravity are examined. As singularity is a critical situation in course of time, study of time paths, in full generality of Equivalence principle, provides two mechanisms to prevent…

General Relativity and Quantum Cosmology · Physics 2007-05-23 K. H. Mariwalla

On the base of years of experience of working on the problem of the physical foundation of quantum mechanics the author offers principles of solving it. Under certain pressure of mathematical formalism there has raised a hypothesis of…

Quantum Physics · Physics 2007-05-23 V. E. Shemi-zadeh

General relativity promotes space-time to a physical, dynamical object subject to equations of motion. Quantum gravity, accordingly, must provide a quantum framework for space-time, applicable on the smallest distance scales. Just like…

General Relativity and Quantum Cosmology · Physics 2010-02-15 Martin Bojowald

There ought to exist a reformulation of quantum theory which does not depend on classical time. To achieve such a reformulation, we introduce the concept of an atom of space-time-matter (STM). An STM atom is a classical non-commutative…

General Relativity and Quantum Cosmology · Physics 2019-07-17 Shounak De , Tejinder P. Singh , Abhinav Varma

Advances in our understanding of the physical universe have impacted dramatically on how we view ourselves. Right at the core of all modern thinking about the universe is the assumption that dynamics is an elemental feature that exists…

Quantum Physics · Physics 2018-07-04 Joan A. Vaccaro

It is well known that in quantum gravity, the very geometry of space and time is subject to continual fluctuation. The mathematical formulation for this old theory is still lacking. This article formulates this more than forty-year-old…

General Relativity and Quantum Cosmology · Physics 2024-09-27 Behzad Tajahmad

The appearance of infinity together with collapsing quantum state due to the observation or interaction, which are two challenging features of quantum field theory, become very serious problems in quantum gravity as well as in quantum…

General Relativity and Quantum Cosmology · Physics 2023-04-14 M. V. Takook

It is unclear whether an observable notion of time exists in quantum gravity even in principle because spacetime itself fluctuates. We propose a form of observable time in perturbative quantum gravity. First, we define an elapsed proper…

High Energy Physics - Theory · Physics 2025-06-23 Allic Sivaramakrishnan

The expansion of our universe, when followed backward in time, implies that it emerged from a phase of huge density, the big bang. These stages are so extreme that classical general relativity combined with matter theories is not able to…

General Relativity and Quantum Cosmology · Physics 2007-05-23 Martin Bojowald

This paper is a continuation of the paper [V.S.Mashkevich, gr-qc/9409010]. Indeterministic quantum gravity is a theory that unifies general relativity and quantum theory involving indeterministic conception, i.e., quantum jumps. By the same…

General Relativity and Quantum Cosmology · Physics 2016-08-31 Vladimir S. Mashkevich