Monthly Archives: January 2015

Improved constraint on the primordial gravitational-wave density

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Florent Robinet and Sophie Henrot-Versille

Sophie Henrot-Versillé and Florent Robinet are research associates at the Laboratoire de l’Accélérateur Linéaire d’Orsay

Many cosmological models predict the existence of a stochastic Gravitational-Wave (GW) background produced just after the universe was born. As gravitational waves do not interact with matter, their detection would give us a unique and pristine probe to study the very first instants of the Universe: when it was 50 orders of magnitude younger than its age at the epoch of the photon decoupling. Such a detection would be as important as the discovery of the Cosmological Microwave Background (CMB). CMB studies tell us what the universe looked like when it became optically thin (~300,000 years after the Big Bang). They help us to establish the standard ΛCDM model of cosmology and to understand the important role of inflation. Continue reading →

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 →