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2-Aug-2005 14:17:25 UT

Background Science

Einstein's general relativity, published in 1915-16, revealed that cosmic space is not a mere void, but takes part in the work of the Universe. The Sun, the Earth and other massive bodies deform the space around them, so that nearby objects alter course. This is the force of gravity. But if a massive body changes, for example when stars revolve around one another, or an exploding star collapses untidily to make a black hole, the deformation of space also changes. The local alteration affects farther regions. A disturbance travels outwards at the speed of light, as a gravitational wave that alternately stretches space and squeezes it.

Indirect evidence for gravitational waves comes from a pair of pulsars (pulsating radio stars) that orbit around one another. They are losing energy at exactly the rate expected if they are emitting gravitational waves in accordance with Einstein's predictions. The astronomers who made this discovery won the Nobel physics prize. Similar recognition can be expected for the direct detection of the waves.

Two big benefits to science, and to human understanding of the Universe we live in, will come from the discovery of gravitational waves. It will confirm, or perhaps modify, Einstein's great theory, which is currently under attack because it seems to disagree with quantum theory, another pillar of modern physics.

Secondly, the discovery will open a completely new window on the Universe, using neither light nor its invisible counterparts (X-rays, radio etc.) but the tremors of space itself. Sources of gravitational waves detectable by LISA should include newly forming black holes, colliding black holes and, as a matter for routine observation, pairs of stars orbiting close together. There may even be gravitational waves from the origin of the Universe.

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