What are Gravitational Waves?

Gravitational waves are 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Einstein's mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that 'waves' of distorted space would radiate from the source (like the movement of waves away from a stone thrown into a pond). Furthermore, these ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself.

The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and the remnants of gravitational radiation created by the birth of the Universe itself.

However, the changes in distance caused by gravitational waves are tiny: even the gravitational wave produced by a powerful event in our vicinity, like a supernova explosion within the Milky Way, changes the total distance between Earth and Sun only by about the diameter of a hydrogen atom - and that merely for several thousandths of a second. For shorter distances the effect is correspondingly smaller: when measuring over a distance of only one kilometer a change of a thousandths of the diameter of a proton has to be detected to determine the passing of a gravitational wave. This is the effect that Gravitational-Wave Observatories measure. The great challenge is to get rid of the many disturbances, like air pressure and temperature fluctuations as well as seismic vibrations of all sorts, that would conceal a signal.