Grappling with gravity

• 09 October 2004
• Stephen Battersby
• Magazine issue 2468

SHAKE your fist and you shake the universe. Just by moving the mass of your hand back and forth, you are sending out ripples in space and time - pieces of travelling gravity that distort everything they meet.

The wobble in your hand's gravitational influence spreads out in all directions, moving at the speed of light. Because these waves are actually changes in space-time, they warp any object they meet, alternately squashing and stretching it in different directions.

But only a little bit. Astrophysicists reckon that to spot the gravity waves from events such as black hole collisions, detectors might need to spot distortions of about one part in 1021 - equivalent to a change in the distance from London to New York by the width of a uranium nucleus. Seeing the gravity waves created by the inflating universe will be even trickier.

To reach such astonishing sensitivity, physicists and ...