scholarly journals Metrics with Zero and Almost-zero Einstein Action in Quantum Gravity

2019 ◽  
Author(s):  
Giovanni Modanese
Keyword(s):  
Gravitational Field ◽  
Quantum Gravity ◽  
Scalar Curvature ◽  
Spontaneous Polarization ◽  
Spherical Symmetry ◽  
Metropolis Algorithm ◽  
Vacuum Fluctuations ◽  
Spacetime Foam

We generate numerically on a lattice an ensemble of stationary metrics, with spherical symmetry, which have Einstein action SE « ħ. This is obtained through a Metropolis algorithm with weight exp(-β2SE2) and β » ħ-1. The squared action in the exponential allows to circumvene the problem of the non-positivity of SE. The discretized metrics obtained exhibit a spontaneous polarization in regions of positive and negative scalar curvature. We compare this ensemble with a class of continuous metrics previously found, which satisfy the condition SE=0 exactly, or in certain cases even the stronger condition R(x)=0 for any x. All these gravitational field configurations are of considerable interest in quantum gravity, because they represent possible vacuum fluctuations and are markedly different from Wheeler's ''spacetime foam''.

scholarly journals Metrics with Zero and Almost-Zero Einstein Action in Quantum Gravity

Symmetry ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1288 ◽  
Author(s):  
Giovanni Modanese
Keyword(s):  
Gravitational Field ◽  
Quantum Gravity ◽  
Scalar Curvature ◽  
Spontaneous Polarization ◽  
Spherical Symmetry ◽  
Metropolis Algorithm ◽  
Vacuum Fluctuations ◽  
Spacetime Foam

We generate numerically on a lattice an ensemble of stationary metrics, with spherical symmetry, which have Einstein action SE « ћ. This is obtained through a Metropolis algorithm with weight exp(−β2S2E) and β » ћ−1. The squared action in the exponential allows to circumvene the problem of the non-positivity of SE. The discretized metrics obtained exhibit a spontaneous polarization in regions of positive and negative scalar curvature. We compare this ensemble with a class of continuous metrics previously found, which satisfy the condition SE = 0 exactly, or in certain cases even the stronger condition R(x) = 0 for any x. All these gravitational field configurations are of considerable interest in quantum gravity, because they represent possible vacuum fluctuations and are markedly different from Wheeler’s “spacetime foam”.

scholarly journals Midisuperspace foam and the cosmological constant

2021 ◽  
Author(s):  
Steven Carlip
Keyword(s):  
Initial Data ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Spherical Symmetry ◽  
Planck Scale ◽  
Stationary States ◽  
Infinite Class ◽  
Probability Current ◽  
Spacetime Foam ◽  
Large Quantum

Abstract Wheeler's conjectured "spacetime foam" -- large quantum fluctuations of spacetime at the Planck scale -- could have important implications for quantum gravity, perhaps even explaining why the cosmological constant seems so small. Here I explore this problem in a midisuperspace model consisting of metrics with local spherical symmetry. Classically, an infinite class of ``foamy'' initial data can be constructed, in which cancellations between expanding and contracting regions lead to a small average expansion even if Λ is large. Quantum mechanically, the model admits corresponding stationary states, for which the probability current is also nearly zero. These states appear to describe a self-reproducing spacetime foam with very small average expansion, effectively hiding the cosmological constant.

scholarly journals INTERFACE OF GRAVITATIONAL AND QUANTUM REALMS

2002 ◽  
Vol 17 (15n17) ◽  
pp. 1135-1145 ◽  
Author(s):  
D. V. AHLUWALIA
Keyword(s):  
Quantum Gravity ◽  
Quantum Interference ◽  
Physical Reality ◽  
Superconducting Quantum Interference Devices ◽  
Superconducting Quantum Interference ◽  
Quantum Gravity Phenomenology ◽  
Wave Particle Duality ◽  
General Relativistic ◽  
Relativistic Description ◽  
Spacetime Foam

The talk centers around the question: Can general-relativistic description of physical reality be considered complete? On the way I argue how – unknown to many a physicists, even today – the "forty orders of magnitude argument" against quantum gravity phenomenology was defeated more than a quarter of a century ago, and how we now stand at the possible verge of detecting a signal for the spacetime foam, and studying the gravitationally-modified wave particle duality using superconducting quantum interference devices.

“Prehistoric” Quantum Gravity

2020 ◽  
pp. 41-70
Author(s):  
Dean Rickles
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Gravitational Field ◽  
Quantum Gravity ◽  
Philosophical Nature

In this chapter we examine the very earliest work on the problem of quantum gravity (understood very liberally). We show that, even before the concept of the quantization of the gravitational field in 1929, there was a fairly lively investigation of the relationships between gravity and quantum stretching as far back as 1916, and certainly no suggestion that such a theory would not be forthcoming. Indeed, there are, rather, many suggestions explicitly advocating that an integration of quantum theory and general relativity (or gravitation, at least) is essential for future physics, in order to construct a satisfactory foundation. We also see how this belief was guided by a diverse family of underlying agendas and constraints, often of a highly philosophical nature.

Quantum superposition of massive bodies

2020 ◽  
Vol 29 (11) ◽  
pp. 2041003
Author(s):  
Robert M. Wald
Keyword(s):  
Gravitational Field ◽  
Gravitational Radiation ◽  
The Body ◽  
Vacuum Fluctuations ◽  
Quantum Superposition ◽  
Gedanken Experiment ◽  
Work Done

I describe the work done in collaboration with A. Belenchia, F. Giacomini, E. Castro-Ruiz, C. Bruckner and M. Aspelmeyer that analyzes a gedanken experiment involving a massive body that is put into a quantum superposition. Remarkably, even for a nonrelativistic body, both vacuum fluctuations of the gravitational field and the quantization of gravitational radiation are essential in order to avoid inconsistencies. In addition, it is essential that the quantum body be viewed as entangled with its own Newtonian-like gravitational field in order to understand how the body may become entangled with other massive bodies via gravitational interactions.

scholarly journals Chiral Vacuum Fluctuations in Quantum Gravity

2011 ◽  
Vol 106 (12) ◽  
Author(s):  
João Magueijo ◽  
Dionigi M. T. Benincasa
Keyword(s):  
Quantum Gravity ◽  
Vacuum Fluctuations

DIMENSION EMERGENCE, HOLOGRAPHY AND QUANTUM GRAVITY

2011 ◽  
Vol 26 (21) ◽  
pp. 3679-3696
Author(s):  
YU-LEI FENG ◽  
LI-XIN XU ◽  
YU-TING WANG
Keyword(s):  
Quantum Mechanics ◽  
Gravitational Field ◽  
Quantum Gravity ◽  
Quantum System ◽  
Alternative Interpretation ◽  
Reduction Mechanism ◽  
Dimensional Theory ◽  
Shift Vector ◽  
Higher Dimensional ◽  
Holography Principle

In this paper, we try to give an alternative interpretation of the holography principle. We argue that the space or time may be regarded as emerging from quantum mechanics as an evolutive parameter. The lower D-dimensional theory is related to a corresponding (D+1)-theory by a mysterious quantum system. Then from the higher-dimensional theory, under a new dimension reduction mechanism we obtain the corresponding results. We also try to incorporate the gauge field into the reduction, roughly identifying Aμ with Nμ which is the shift vector in the ADM-like decomposition of space–time metric. In the end, we extend to the gravitational field, and obtain a relation [Formula: see text] with a cutoff factor κ, from a different view.

scholarly journals CMB ANISOTROPIES REVEAL QUANTIZED GRAVITY

2005 ◽  
Vol 20 (07) ◽  
pp. 509-517 ◽  
Author(s):  
KEN-JI HAMADA ◽  
TETSUYUKI YUKAWA
Keyword(s):  
Quantum Gravity ◽  
Scalar Curvature ◽  
Early Universe ◽  
Time Constant ◽  
Power Spectra ◽  
Induced Gravity ◽  
Sharp Fall ◽  
Conformal Field ◽  
Expansion Time ◽  
Renormalizable Model

A novel primordial spectrum with a dynamical scale of quantum gravity origin is proposed to explain the sharp fall off of the angular power spectra at low multipoles in the COBE and WMAP observations. The spectrum is derived from quantum fluctuations of the scalar curvature in a renormalizable model of induced gravity. This model describes the very early universe by the conformal field fluctuating about an inflationary background with the expansion time constant of order of the Planck mass.

Negative scalar curvature as a characteristic of the elasticity of the gravitational field

2008 ◽  
Vol 53 (8) ◽  
pp. 425-427
Author(s):  
S. S. Gershteĭn ◽  
A. A. Logunov ◽  
M. A. Mestvirishvili
Keyword(s):  
Gravitational Field ◽  
Scalar Curvature
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