Journal Club

Seminar Room

If you want to propose a paper, you can contact Supratim Das Bakshi (sdb AT ugr.es)

Tuesday 15th of February, 2022

Gravitational wave memory and the wave equation

Gravitational wave memory and its electromagnetic analog are shown to be straightforward consequences of the wave equation. From Maxwell's equations one can derive a wave equation for the electric field, while from the Bianchi identity one can derive a wave equation for the Riemann tensor in linearized gravity. Memory in both cases is derived from the structure of the source of those wave equations.
Subjects: General Relativity and Quantum Cosmology (gr-qc)
Cite as: arXiv:2201.05543 [gr-qc]
  (or arXiv:2201.05543v1 [gr-qc] for this version)

Submission history

From: David Garfinkle [view email
[v1] Fri, 14 Jan 2022 16:29:16 UTC (9 KB)
 

Memory effect explained for the general public in: 
https://www.quantamagazine.org/gravitational-waves-should-permanently-distort-space-time-20211208/


presented by Javi Olmedo

 

A Gravitational Entropy Proposal

We propose a thermodynamically motivated measure of gravitational entropy based on the Bel-Robinson tensor, which has a natural interpretation as the effective super-energy-momentum tensor of free gravitational fields. The specific form of this measure differs depending on whether the gravitational field is Coulomb-like or wave-like, and reduces to the Bekenstein-Hawking value when integrated over the interior of a Schwarzschild black hole. For scalar perturbations of a Robertson-Walker geometry we find that the entropy goes like the Hubble weighted anisotropy of the gravitational field, and therefore increases as structure formation occurs. This is in keeping with our expectations for the behaviour of gravitational entropy in cosmology, and provides a thermodynamically motivated arrow of time for cosmological solutions of Einstein's field equations. It is also in keeping with Penrose's Weyl curvature hypothesis.
Comments: 17 pages
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
Journal reference: Class. Quant. Grav. 30 (2013) 125009
DOI: 10.1088/0264-9381/30/12/125009
Cite as: arXiv:1303.5612 [gr-qc]
  (or arXiv:1303.5612v2 [gr-qc] for this version)

Submission history

From: Timothy Clifton [view email
[v1] Fri, 22 Mar 2013 13:29:55 UTC (17 KB)
[v2] Mon, 20 May 2013 08:54:13 UTC (18 KB)

presented by Antonio Manso