This discovery could help to reveal the dynamics of space itself
PHYSICISTS and astronomers are agog. Experimenters have reported the first detection of a phenomenon that has been long predicted: bursts of gravitational waves generated by cosmic collisions of black holes. It is not unknown for hyped-up scientific claims to be mistaken or exaggerated. I count myself a sceptic, but what was claimed last week was the culmination of decades of effort by scientists and engineers with high credentials – and this time I was fully convinced. This detection is indeed a big deal: one of the great discoveries of the decade – up there with the detection of the Higgs particle, which was a capstone to the so-called standard model of particle physics, developed over several decades. Likewise, gravitational waves – vibrations in the fabric of space itself – are a crucial and distinctive consequence of Einstein’s theory of general relativity. This theory tells us the force of gravity is best understood as a “warping” of space itself. When gravitating objects move, they generate a “ripple” in space itself. When such a ripple passes Earth, our local space is alternately stretched and compressed, rather as, when a stone is thrown into a pond, the induced outward-moving wave causes the water at any point to cyclically rise and fall – but by a tiny amount. The detection has been delayed because the quest involves detecting a very elusive effect and again requires large-scale and expensive instruments. Why is the effect so small and elusive? It’s basically because gravity is such a weak force. Even planets orbiting stars, or pairs of stars orbiting each other, don’t emit at a detectable level. Quite apart from offering a completely new vindication of Einstein’s theory, these results will deepen our understanding of stars and galaxies. Astronomical evidence on black holes and massive stars is limited – it was hard to predict how many would be within range. Pessimists thought the events might be so rare that even the new and improved Ligo wouldn’t detect anything for a year or two. But unless the experimenters have had exceptional luck, it looks as though a new kind of astronomy has opened up, revealing the dynamics of space itself, rather than the material that pervades it. Two European detectors are joining the search, and these discoveries will stimulate wider efforts to exploit this fundamentally new channel of information about cosmic phenomena.