Yearly Archives: 2014

Even a tiny cosmological constant casts a long shadow

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Aruna Kesavan

Aruna Kesavan is a graduate student at the Pennsylvania State University

How safe is it to ignore the cosmological constant in the study of isolated systems and gravitational waves?

Analysis of isolated systems, such as stars, black holes and compact binaries, has dominated gravitational science, spanning diverse areas that include geometric analysis, computational relativity, gravitational waves, relativistic astrophysics and quantum black-holes. For example, over the past four decades, powerful positive energy theorems were proved, a theory of gravitational radiation in exact general relativity was developed, computational simulations were carried out to extract energy-momentum emitted during binary mergers, and evaporation of black holes was analyzed using appropriate Hilbert spaces of asymptotic states.

These advances are based on the Bondi-Penrose framework for zero cosmological constant \Lambda. But by now observations have Continue reading →

Non-CMC solutions to the Einstein constraint equations on asymptotically Euclidean manifolds with apparent horizon boundaries

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Juan A. Valiente Kroon

Juan A. Valiente Kroon works on various aspects of mathematical Relativity and, in particular, on applications of conformal methods to analyse the global properties of spacetimes.

The construction of physically realistic data for the Einstein field equations is one of the great challenges of the Cauchy problem in General Relativity. In this paper C. Meier and M. Holst show how to construct solutions to the constraint equations of General Relativity representing data which will evolve, assuming that a certain form of weak cosmic censorship holds, into a spacetime containing one or more black holes.

The most studied procedure for solving the constraint equations is the so-called conformal method. This approach can be traced back to the pioneering work of Continue reading →

Video: Hunting for gravitational waves using pulsars

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Louise Mayor

Louise Mayor is features editor of Physics World

As features editor of Physics World magazine, my search for stories to share with our readers takes me far and wide – from nuclear reactors to the quietest lab in the world. But sometimes I need look no further than the very office in which I work. That’s because I share my workplace with the staff behind nearly 70 journals published by IOP Publishing. So it was that one lunchtime earlier this year, I got chatting to Adam Day, publisher of Classical and Quantum Gravity (CQG).

Day began telling me about a method of detecting gravitational waves I’d not heard of before, and in no time at all I was hooked. First proposed in the 1970s, the method involves Continue reading →

Achieving resonance in the Advanced LIGO gravitational-wave interferometer

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Alexa Staley

Alexa Staley is a PhD candidate at Columbia University in the City of New York, and has been working as a graduate student at the LIGO Hanford Observatory in Richland, WA.

The next generation gravitational wave interferometers, known as Advanced LIGO, located in Hanford, WA and Livingston, LA have been installed and are in the process of achieving a sensitivity required for the first direct detection of a gravitational wave. The goal of their design is to measure a gravitational strain as small as 4×10–24/√Hz, requiring a length resolution of approximately 10–19 rms within a 100 Hz bandwidth. This high sensitivity demands multiple optical cavities to enhance the response Continue reading →

Focus issue: Astrophysics and general relativity of dense stellar systems

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Clifford Will and Pau Amaro-Seoane

Guest Editors: Clifford Will and Pau Amaro-Seoane

We invite you to read the latest CQG focus issue on “Astrophysics and General Relativity of dense stellar systems“, which is available to read now.

Dense stellar systems such as galactic nuclei and stellar clusters are unique laboratories, not only for astrophysics, but also for general relativity. The complexity of these systems is such that, in spite of a huge theoretical, observational and numerical effort there are still a large number of open key questions. This focus issue on the “Astrophysics and General Relativity of Dense Stellar Systems” brings together an array of invited articles on important aspects of these questions.

We hope that you will enjoy reading the articles in the focus issue; all of which are free for a period of time following publication.

Black holes against the universe – particle and photon orbits in McVittie spacetimes

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Brien Nolan

Brien Nolan is a Senior Lecturer in the School of Mathematical Sciences, Dublin City University

Black holes have a potential technological application that is frequently overlooked: they allow you to look at the back of your own head. This could be useful for checking that your tie is properly tucked into your shirt collar, or – perhaps more relevant for physicists – that your pony tail is straight. This technology relies on the fact that there exist circular photon orbits in all members of the Kerr-Newman-de Sitter family of spacetimes for which the parameters (mass, charge and cosmological constant) correspond to a black hole.

The question arises as to whether this characteristic feature of electro-vac Continue reading →

Focus issue: Relativistic effects in cosmology

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Kazuya Koyama

Kazuya Koyama is a Reader in Cosmology in the Institute of Cosmology and Gravitation, at the University of Portsmouth,

I am very pleased to bring you this focus issue summarising the recent developments in computing relativistic effects in cosmology.

The issue consists of two parts, with the first part examining general relativistic formulations of the observed over-density of galaxies.

The second part discusses relativistic effects on the formation of large scale structures.

The authors pioneered the development of our understanding of general relativistic effects in cosmological observations and we hope that this focus issue will be a basis for further advancement of the field. Continue reading →

Movie Review of Interstellar, by Richard Price

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See more Interstellar posters

Image copyright Warner Bros and Paramount Pictures

CQG has never published a movie review before. It is therefore with appropriate humility that I offer a review of Interstellar.  This scifi epic wins the historic honor because it lists a physicist, Kip Thorne, as an executive producer, and is advertised as based on his theories. Indeed, the movie plot and graphics do involve ideas of relativity in very important ways.

In the spirit of disclosure I state, right up front, that I am not a fan of science fiction, but am a fan of Kip Thorne; like many of his former students I have remained a friend.  My fan/antifan biases should cancel and leave me to do the objective job that a scientist is expected to do.

This is not, of course, a review for the general public. CQG is seldom found in the waiting room of dentists. If you Continue reading →

Holographic entanglement obeys strong subadditivity

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Aron Wall

Aron Wall is a member of the School of Natural Sciences at the Institute for Advanced Study. In his spare time he blogs at Undivided Looking. He was the 2013 recipient of the Bergmann-Wheeler thesis prize, which is sponsored by Classical and Quantum Gravity.

Gauge-gravity duality allows us to calculate properties of certain quantum field theories (QFT) from classical general relativity. One famous piece of this conjecture, due to Ryu and Takayanagi, relates the entanglement entropy in a QFT region to the area of a surface in the gravitational theory. In addition to being a clue about quantum gravity, this proposal is one of the few tools which allow us to calculate entanglement entropy analytically. Since the entanglement entropy is of increasing interest for field theory and condensed matter applications, it is important to check if the conjecture is true.

One important property of the entropy is strong subadditivity (SSA). This quantum inequality says that the sum of the entropies in two regions is always greater than the sum of the entropies of their union and intersection. My article uses proof Continue reading →

Black holes as beads on cosmic strings

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Amjad Ashoorioon and Robert Mann

Amjad Ashoorioon (left) is a Senior Research Associate at the physics department of Lancaster University in the United Kingdom. Robert B. Mann (right) is a Professor of Physics and Applied Mathematics at the University of Waterloo, Ontario, Canada.

Cosmic strings have been a source of fascination in cosmology since Tom Kibble first proposed their existence 40 years ago. Like an imperfection in a solidifying crystal, a cosmic string is a thread of energy that might have formed in the early universe during a symmetry breaking phase transition. Twenty years ago Ruth Gregory pointed out that a black hole could have a cosmic string as a single “hair”.   Turning this idea around, in this article we have proposed that a Continue reading →