* Astronomy

Precise Radio-Telescope Measurements Advance Frontier Gravitational Physics
Scientists using a continent-wide array of radio telescopes have made an extremely precise measurement of the curvature of space caused by the Sun's gravity, and their technique promises a major contribution to a frontier area of basic physics.

"Measuring the curvature of space caused by gravity is one of the most sensitive ways to learn how Einstein's theory of General Relativity relates to quantum physics. Uniting gravity theory with quantum theory is a major goal of 21st-Century physics, and these astronomical measurements are a key to understanding the relationship between the two" - Sergei Kopeikin of the University of Missouri.

Kopeikin and his colleagues used the National Science Foundation's Very Long Baseline Array (VLBA) radio-telescope system to measure the bending of light caused by the Sun's gravity to within one part in 30,000. With further observations, the scientists say their precision technique can make the most accurate measure ever of this phenomenon.

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(18 Dec 2007)
Time is running out - literally, says scientist
Scientists have come up with the radical suggestion that the universe's end may come not with a bang but a standstill - that time could be literally running out and could, one day, stop altogether.
The idea that time itself could cease to be in billions of years - and everything will grind to a halt - has been set out by Professor José Senovilla, Marc Mars and Raül Vera of the University of the Basque Country, Bilbao, and University of Salamanca, Spain.

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Title: Ultraviolet Behaviour of [script N]=8 Supergravity at Four Loops
Authors: Z. Bern, J. J. M. Carrasco, L. J. Dixon, H. Johansson, and R. Roiban

We describe the construction of the complete four-loop four-particle amplitude of [script N]=8 supergravity. The amplitude is ultraviolet finite, not only in four dimensions, but in five dimensions as well. The observed extra cancellations provide additional nontrivial evidence that [script N]=8 supergravity in four dimensions may be ultraviolet finite to all orders of perturbation theory.

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Title: Prospects for constraining quantum gravity dispersion with near term observations
Authors: Giovanni Amelino-Camelia, Lee Smolin
(Version v3)

We discuss the prospects for bounding and perhaps even measuring quantum gravity effects on the dispersion of light using the highest energy photons produced in gamma ray bursts measured by the Fermi telescope. These prospects are brighter than might have been expected as in the first 10 months of operation Fermi has reported so far eight events with photons over 100 MeV seen by its Large Area Telescope (LAT). We review features of these events which may bear on Planck scale phenomenology and we discuss the possible implications for the alternative scenarios for in-vacua dispersion coming from breaking or deforming of Poincare invariance. Among these are semi-conservative bounds, which rely on some relatively weak assumptions about the sources, on subluminal and superluminal in-vacuo dispersion. We also propose that it may be possible to look for the arrival of still higher energy photons and neutrinos from GRB's with energies in the range 10^14 - 10^17 eV. In some cases the quantum gravity dispersion effect would predict these arrivals to be delayed or advanced by days to months from the GRB, giving a clean separation of astrophysical source and spacetime propagation effects.

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