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 Prediction for the cosmological constant and constraints on SUSY GUTs in resummed quantum gravity

2018 ◽  
Vol 33 (29) ◽  
pp. 1830028
Author(s):  
B. F. L. Ward
Keyword(s):  
General Theory ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Uncertainty Principle ◽  
Planck Scale ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Heisenberg Uncertainty Principle ◽  
Heisenberg Uncertainty

Working in the context of the Planck scale cosmology formulation of Bonanno and Reuter, we use our resummed quantum gravity approach to Einstein’s general theory of relativity to estimate the value of the cosmological constant as [Formula: see text]. We show that SUSY GUT models are constrained by the closeness of this estimate to experiment. We also address various consistency checks on the calculation. In particular, we use the Heisenberg uncertainty principle to remove a large part of the remaining uncertainty in our estimate of [Formula: see text].

scholarly journals Einstein–Heisenberg consistency condition interplay with cosmological constant prediction in resummed quantum gravity

2015 ◽  
Vol 30 (38) ◽  
pp. 1550206 ◽  
Author(s):  
B. F. L. Ward
Keyword(s):  
Quantum Gravity ◽  
Cosmological Constant ◽  
Promising Result ◽  
Consistency Condition ◽  
Planck Scale ◽  
Theory Of Relativity ◽  
Heisenberg Uncertainty Principle ◽  
Recent Success ◽  
Heisenberg Uncertainty ◽  
Frw Model

We argue that our recent success in using our resummed quantum gravity (RQG) approach to Einstein’s general theory of relativity, in the context of the Planck scale cosmology formulation of Bonanno and Reuter, to estimate the value of the cosmological constant [Formula: see text] supports the use of quantum mechanical consistency requirements to constrain the main uncertainty in that very promising result. This main uncertainty, which is due to the uncertainty in the value of the time [Formula: see text] at which the transition from the Planck scale cosmology to the FRW model occurs, is shown to be reduced, by requiring consistency between the Heisenberg uncertainty principle and the known properties of the solutions of Einstein’s equations, from four orders of magnitude to the level of a factor of [Formula: see text]. This lends more credibility to the overall RQG approach itself, in general, and to our estimate of [Formula: see text] in particular.

scholarly journals Spacetime Foam, Midisuperspace, and the Cosmological Constant

Universe ◽  
2021 ◽  
Vol 7 (12) ◽  
pp. 495
Author(s):  
Steven Carlip
Keyword(s):  
Cosmological Constant ◽  
Time Evolution ◽  
Planck Scale ◽  
Quantum Fluctuations ◽  
Spacetime Foam

Perhaps the cosmological constant really is huge at the Planck scale, but is “hidden” by Planck scale quantum fluctuations of spacetime. I briefly review this proposal and provide some evidence, coming from a simplified midisuperspace model, that an appropriate “foamy” structure can do the job of hiding a large cosmological constant, and can persist under time evolution.

scholarly journals Dark energy and quantum gravity

2019 ◽  
Vol 28 (14) ◽  
pp. 1944018 ◽  
Author(s):  
Per Berglund ◽  
Tristan Hübsch ◽  
Djordje Minić
Keyword(s):  
Dark Energy ◽  
String Theory ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Particle Physics ◽  
Dual Space ◽  
Planck Scale ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Sitter Spacetime

Realizing dark energy and the observed de Sitter spacetime in quantum gravity has proven to be obstructed in almost every usual approach. We argue that additional degrees of freedom of the left- and right-movers in string theory and a resulting doubled, noncommutatively generalized geometric formulation thereof can lead to an effective model of dark energy consistent with de Sitter spacetime. In this approach, the curvature of the canonically conjugate dual space provides for the dark energy inducing a positive cosmological constant in the observed spacetime, whereas the size of the above dual space is the gravitational constant in the same observed de Sitter spacetime. As a hallmark relation owing to a unique feature of string theory which relates short distances to long distances, the cosmological constant scale, the Planck scale and the effective TeV-sized particle physics scale must satisfy a see-saw-like formula — precisely the generic prediction of certain stringy cosmic brane type models.

scholarly journals How to hide a cosmological constant

2019 ◽  
Vol 28 (14) ◽  
pp. 1943004 ◽  
Author(s):  
Steven Carlip
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Cosmological Constant ◽  
Planck Scale ◽  
Quantum Field ◽  
Vacuum Fluctuations ◽  
And Topology ◽  
Spacetime Foam

Naive calculations in quantum field theory suggest that vacuum fluctuations should induce an enormous cosmological constant. What if these estimates are right? I argue that even a huge cosmological constant might be hidden in Planck-scale fluctuations of geometry and topology — what Wheeler called “spacetime foam” — while remaining virtually invisible macroscopically.

scholarly journals Noncommutative Relativistic Spacetimes and Worldlines from 2 + 1 Quantum (Anti-)de Sitter Groups

2017 ◽  
Vol 2017 ◽  
pp. 1-19 ◽  
Author(s):  
Ángel Ballesteros ◽  
N. Rossano Bruno ◽  
Francisco J. Herranz
Keyword(s):  
Quantum Gravity ◽  
Cosmological Constant ◽  
Lie Algebras ◽  
Deformation Parameter ◽  
Planck Scale ◽  
Quantum Deformation ◽  
De Sitter ◽  
Planck Length ◽  
Unified Approach ◽  
Drinfel’D Double

Theκ-deformation of the (2 + 1)D anti-de Sitter, Poincaré, and de Sitter groups is presented through a unified approach in which the curvature of the spacetime (or the cosmological constant) is considered as an explicit parameter. The Drinfel’d-double and the Poisson–Lie structure underlying theκ-deformation are explicitly given, and the three quantum kinematical groups are obtained as quantizations of such Poisson–Lie algebras. As a consequence, the noncommutative (2 + 1)D spacetimes that generalize theκ-Minkowski space to the (anti-)de Sitter ones are obtained. Moreover, noncommutative 4D spaces of (time-like) geodesics can be defined, and they can be interpreted as a novel possibility to introduce noncommutative worldlines. Furthermore, quantum (anti-)de Sitter algebras are presented both in the known basis related to 2 + 1 quantum gravity and in a new one which generalizes the bicrossproduct one. In this framework, the quantum deformation parameter is related to the Planck length, and the existence of a kind of “duality” between the cosmological constant and the Planck scale is also envisaged.

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 Prediction for the cosmological constant in resummed quantum gravity and constraints on susy GUTs

2015 ◽  
Vol 24 (03) ◽  
pp. 1530009
Author(s):  
B. F. L. Ward
Keyword(s):  
General Theory ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Planck Scale ◽  
Theoretical Uncertainty ◽  
Unified Theory ◽  
Grand Unified Theory ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Theoretical Issues

We use our resummed quantum gravity approach to Einstein's general theory of relativity in the context of the Planck scale cosmology formulation of Bonanno and Reuter to estimate the value of the cosmological constant such that ρΛ = (0.0024 eV)4. We argue that the closeness of this estimate to experiment constrains Supersymmetric Grand Unified Theory (susy GUT) models. We discuss in turn various theoretical issues that have been raised about the approach itself as well as about the application to estimate the cosmological constant. Given the closeness of the estimate to the currently observed value, we also discuss the theoretical uncertainty in the estimate-at this time, we argue it is still large.

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 MEASUREMENTS AND INFORMATION IN SPIN FOAM MODELS

2012 ◽  
Vol 27 (28) ◽  
pp. 1250164
Author(s):  
J. MANUEL GARCÍA-ISLAS
Keyword(s):  
Information Theory ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Shannon Entropy ◽  
Three Dimensional ◽  
Spin Network ◽  
Spin Foam Models ◽  
Foam Model ◽  
Spin Foam Model ◽  
Spin Foam

In the three-dimensional spin foam model of quantum gravity with a cosmological constant, there exists a set of observables associated with spin network graphs. A set of probabilities is calculated from these observables, and hence the associated Shannon entropy can be defined. We present the Shannon entropy associated with these observables and find some interesting bounded inequalities. The problem relates measurements, entropy and information theory in a simple way which we explain.

Sign in / Sign up

Export Citation Format

Share Document