Nature: Einstein passes cosmic test

[bystander]

Einstein passes cosmic test
Nature News - 2010 March 10

General relativity fits survey observations but there's still room for its rivals.

It's another victory for Einstein — albeit not a resounding one. General relativity has been confirmed at the largest scale yet. But the galactic tests used to put the theory through its paces cannot rule out all rival theories of gravity.

Cosmology: Gravity tested on cosmic scales

• Nature 464, 172-173 (11 March 2010) | doi:10.1038/464172a

Einstein's theory of general relativity has been tested — and confirmed — on scales far beyond those of our Solar System. But the results don't exclude all alternative theories of gravity.

Our understanding of the physics that underlies the dynamical evolution of the Universe and the development of cosmic structure is driven by astronomical observations. Historically, measurements on galaxy and larger cosmological scales conflicted with predictions based on a cosmological model that combined Albert Einstein's theory of gravity (general relativity) and the standard model of particle physics.

Confirmation of general relativity on large scales from weak lensing and galaxy velocities

• Nature 464, 256-258 (11 March 2010) | doi:10.1038/nature08857

Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, E_G, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to ‘galaxy bias’ (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of E_G different from the general relativistic prediction because, in these theories, the ‘gravitational slip’ (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect.

[bystander]

Study validates general relativity on cosmic scale, existence of dark matter
PhysOrg General Physics - 2010 March 10

An analysis of more than 70,000 galaxies by University of California, Berkeley, University of Zurich and Princeton University physicists demonstrates that the universe - at least up to a distance of 3.5 billion light years from Earth - plays by the rules set out 95 years ago by Albert Einstein in his General Theory of Relativity.

By calculating the clustering of these galaxies, which stretch nearly one-third of the way to the edge of the universe, and analyzing their velocities and distortion from intervening material, the researchers have shown that Einstein's theory explains the nearby universe better than alternative theories of gravity.

http://www.sciencedaily.com/releases/20 ... 134152.htm
http://www.space.com/scienceastronomy/g ... 00310.html

[bystander]

Foiling an Attack on General Relativity
Lawrence Berkeley National Laboratory - 2010 March 11

In an attempt to explain away dark matter and dark energy, some theorists have offered new theories of gravity that try to improve on Einstein’s General Theory of Relativity. A new study inspired by the work of a Berkeley Lab cosmologist indicates that at least one of these new theories is wrong.

Einstein’s General Theory of Relativity explains gravity in terms of the curvature of space by mass. Dating from the second decade of the 20th century, after more than 90 years it is still the basis of our understanding of how gravity works to shape the cosmos.

But as evidence for a universe filled with dark matter and dark energy has mounted, General Relativity’s ability to explain the structure and expansion of the universe has faced new challenges.

Some theorists deny that dark matter or dark energy exist, suggesting that there’s a problem with General Relativity’s handling of gravity. They hope to explain away the apparent gravitational effects of dark matter, and the apparent accelerating expansion of the universe caused by dark energy, with appeals to modified gravitational theories.

UC Berkeley press release