Monthly Archives: May 2014

Testing the weak equivalence principle with atom interferometry in space

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Clifford Will

Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity

The Weak Equivalence Principle (WEP) is one of the three pillars that support all metric theories of gravity, and testing it to high precision has occupied experimentalists for over 100 years. Although many successful tests have been performed, there is still room for new experiments (see this recent CQG focus issue on tests of WEP).

This paper describes in detail a concept called STE-QUEST for testing WEP in space. What makes this different from other space experiments, such as MICROSCOPE, due for launch in 2016, and STEP, still only a design concept, is that those experiments use macroscopic bodies, while STE-QUEST will use fundamentally quantum-mechanical systems: Bose-Einstein condensates of rubidium isotopes. Using atom Continue reading →

A unified description of the second order cosmological density contrast

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In this paper the authors introduce a new way of expressing the relativistic density contrast of matter perturbations in four commonly used gauges, both at first and second orders.

Julien Larena

Dr Julien Larena is a senior lecturer in the Department of Mathematics at Rhodes University, South Africa. His research is centred on relativistic corrections to cosmology, tests of the Copernican principle, and the backreaction issue in cosmology.

This new method is very interesting, since it provides a unified treatment of the density contrast in the various gauges, thus allowing a straightforward comparison of results obtained by other authors in different gauges. This should be useful when computing non-trivial effects such as the properties Continue reading →

A spacetime route to positive mass

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Brien Nolan

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

This paper provides an important, unexpected and very satisfying route to positivity of mass in General Relativity. It shows positivity of the Trautman-Bondi mass in a way that avoids both the heavy differential geometric machinery of the work of Schoen and Yau, and the Continue reading →