The numerical relativity breakthrough in 2005 has provided waveforms of the gravitational wave signal emitted by a compact binary sources that describe the coalescence, the merger of the two compact objects and the ring-down of the newborn object. These waveforms are now more and more often used in gravitational wave searches carried out with interferometric detectors (LIGO, Virgo, GEO and eventually KAGRA), instead of analytical waveforms from Post Newtonian expansion that Continue reading
Whether the gravitational collapse of an astrophysical object leads to a black hole or a naked singularity is one of the most intriguing issues in Einstein’s theory of General Relativity. In many astrophysical situations, the initial conditions are such that a trapped region forms and the gravitational collapse ends in a black hole, in confirmation with the Cosmic Censorship conjecture. However, in recent years Continue reading
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
This paper leads to a discrete action functional on causets.
Lisa Glaser presents some tidy results in the definition of the discrete d’Alembertian operator on a causet in any dimension.
The causet approach to quantum gravity was pioneered by Rafael Sorkin in the 1980s. It approximates the space-time continuum by a discrete structure–a set with a partial order. The causet approach is marked by its minimalist philosophy, capturing Lorentzian manifolds in a discrete net with just Continue reading
This is a very nice article which deserves to be studied carefully by anyone interested in finding solutions to the constraints. In particular, they show how to construct a solution which is far from maximal, and, at the same time, is asymptotically flat. Readers should be aware that the first theorem, Theorem 1.1, covers a much broader range of data than the second theorem, Theorem 1.2. Further, they should be aware that the titles of the theorems ‘Far-from-CMC’ (Theorem 1.1), and ‘Near-CMC’ (Theorem 1.2), especially the second one, are not particularly illuminating.
There are conditions which are surprising. No restriction is placed on Τ2 (other than the AF condition), but we are asked Continue reading