When coupling to matter matters

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Claudia De Rham

Claudia de Rham is an assistant professor at Case Western Reserve University working on cosmology and particle physics and is particularly interested in models of modified gravity and their embedding within consistent field theory frameworks.

How does matter couple in theories involving several metrics? We unveil the possibility for a new effective metric.

While the theory of general relativity will mark its 100 year anniversary next fall, the realization that the expansion of our universe may currently be accelerating has opened up the door for a series of investigations to understand the behavior of gravity at large distances – as large as the current observable Universe or about 1010 light years. Among the different possible modifications of gravity explored in the past decade, theories of gravity which involve several metrics have played a crucial role. The idea that gravity could be the outcome of several interacting metrics is of course not a new concept and such theories have been explored for more than 70 years, but their consistent realization has only been derived very recently in the past few years, and we are finally reaching a stage where we can understand more precisely how matter couples to gravity in such theories. Continue reading →

Movie review of The Theory of Everything by Eric Poisson

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Eric Poisson

Eric Poisson is a professor of physics at the University of Guelph.

The Theory of Everything directed by James Marsh, starring Eddie Redmayne and Felicity Jones.

We physicists can count ourselves lucky these days. We enjoy an unprecedented presence in popular culture, having central characters in today’s most popular sitcom (The Big Bang Theory) and two recent high-profile movies, Interstellar (previously reviewed for CQG+ by Richard Price) and the subject of this review, The Theory of Everything. Science has become cool. Let’s enjoy this while it lasts!

The Theory of Everything relates the life of today’s most famous physicist,  Stephen Hawking. The movie focuses mostly on Stephen’s relationship with his first wife, Jane Wilde Hawking, whose book “Travelling to Infinity” provided the basis for Continue reading →

IOP Gravity Thesis Prize 2015

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Timothy_Clifton

Dr Timothy Clifton is the Secretary of the Gravitational Physics Group, at the Institute of Physics

Submissions are now invited for the £500 prize.

The Gravitational Physics Group at the IOP is inviting submissions for their annual thesis prize.  Recent graduates from PhD programs in any area of gravitational physics, or other related areas, are strongly encouraged to apply.  Details are as follows:

Terms of reference, and elligibility
The prize is awarded for excellence in research and communication skills, as demonstrated by the candidate’s thesis.  All members of the IOP Gravitational Physics Group who passed their viva voce exam during the period 1st January 2012 and 31st December 2014 are elligible.

How to enter
Candidates should email an electronic copy of their thesis to Timothy Clifton, and complete the application form.  All sumissions should be made before the 31st of January 2015.

Furthermore, the winner will be invited to submit a paper to Classical and Quantum Gravity based on the winning thesis which, if accepted, will be made a ‘select article’ in CQG.  They will also be given the opportunity to present their work at one of the UK ‘BritGrav’ meetings. Continue reading →

A new algorithm for gravitational wave propagation

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Casey Handmer and Bela Szilagyi

Casey Handmer (graduate student at Caltech) and Bela Szilagyi (senior research fellow at Caltech) discuss the finer points of null cone geometry.

Gravitational wave evolution – spectral style.

Colliding black holes create powerful ripples in spacetime. Of this we are certain. Directly detecting these ripples, or gravitational waves, is one of the hardest unsolved problems in physics. Inferring physical characteristics of black hole binaries and other gravitationally energetic events from their radiation requires accurate numerical simulation for matched filtering.

But gravitational wave simulations are typically plagued by a lack of gauge invariance. Waveform precision and validity is undermined by coordinate choice and movement. Simulations require an extraction methodology to obtain gauge invariant waveforms. These waveforms are Continue reading →

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 →