Unweaving the cosmic web: Relativity goes large

[n2doc]

12 October 2010 by Pedro Ferreira

AS WE near the centenary of Einstein's general theory of relativity, a quiet revolution is under way. A number of groups around the world are attempting to test the validity of general relativity on the scale of the universe. So far the tests are inconclusive, yet they herald a striking shift in the way that Einstein's theory is perceived. And testing general relativity is rapidly becoming one of the core endeavours for some of the most powerful satellite and ground-based experiments being developed.

Einstein's general theory of relativity has served us well. Yet what if he was off the mark? Don't get me wrong, the theory is remarkably successful at explaining many different phenomena: it allows us to calculate the orbits of all the planets of the solar system with extraordinary accuracy. It also enables us to work out how light is deflected by the deformed space-time around stars and planets. But could we have taken general relativity too far in attempting to predict the evolution of the universe?

It is a striking fact that general relativity has remained unchanged since Einstein first proposed it in 1915. At its heart is our understanding of the force of gravity. Einstein put forward the idea that there is no force of gravity per se. Instead, what we perceive as gravity results from the geometry of space-time. If we place an object - a planet or a star, or indeed anything with mass - into space, it will deform it. Einstein's general theory of relativity gives us unique and exact rules for calculating the extent of this deformation.

Those same rules are with us today, and we have long been mining them, extracting predictions that range from black holes to the big bang. One of the first predictions to emerge was the notion that the universe is expanding. Distant galaxies are moving away from us, and each other, at speeds of tens or hundreds of thousands of kilometres per second. The expansion of the universe was spectacularly confirmed by Edwin Hubble in 1929 and, since then, ever improving observations have enabled us to unravel the history of the expanding universe with increasing precision.

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http://www.newscientist.com/article/mg20827811.500-unweaving-the-cosmic-web-relativity-goes-large.html