Astronomers back up Einstein

An international team of astronomers has confirmed that the universe, at least within a distance of 3.5 billion light years of Earth, obeys Albert Einstein's general theory of relativity."

An international team of astronomers has confirmed that the universe, at least within a distance of 3.5 billion light years of Earth, obeys Albert Einstein's general theory of relativity.

This galaxy cluster from the Sloan Digital Sky Survey contains some of the 70,000 galaxies that were analyzed to test general relativity on the large scale. ((Sloan Digital Sky Survey))

The study, published this week in Nature, throws cold water on some alternative theories of gravity physicists have advanced that don't require the existence of dark matter.

Astronomers have observed that galaxies and clusters of galaxies move as if they're under the influence of a great amount of mass that doesn't give off light, as stars do.

The nature of this mass, called dark matter, still eludes scientists, and some theoreticians have put forth new models of gravity that get rid of it altogether.

Astronomers at the University of California, Berkeley, the University of Zurich and Princeton University analyzed data from more than 70,000 galaxies to test whether the predictions of Einstein's theory or the alternative theories of gravity hold true.

"The nice thing about going to the cosmological scale is that we can test any full, alternative theory of gravity, because it should predict the things we observe," said Uros Seljak, a professor of physics at UC Berkeley and the University of Zurich.

"Those alternative theories that do not require dark matter fail these tests," said Seljak, in a statement.

In particular, the experiment gave a failing grade to a gravity model called the tensor-vector-scalar (TeVeS) theory that tweaked Einstein's theory to get rid of dark matter.

The General Theory of Relativity, a manuscript published by Einstein in 1915, holds that gravity arises because matter warps space and time, meaning that light bends near massive objects, such as the core of a galaxy.

Previous experiments have validated the theory on the scale of the solar system, but not over the large distance of galaxy clusters.

The experiment published this week examined the amount of clustering in observed galaxies and the amount of distortion causing by light bending as it passed through galaxies, expressed in a quantity called EG.

Different models of the universe have different predictions for this amount and the prediction of EG derived from Einstein's theory (0.4) was in close agreement with the observed results (0.39).