The search for gravitational waves

A recent news article from the BBC on the GEO 600 gravitational wave observatory prompted me to do a bit of reading up on gravitational waves and current research into them.

What are gravity waves ?


The easiest way to think of gravitational waves is as ripples in the fabric of space-time. If you throw a pebble into a lake you get ripples in the water surface - waves. Einstein's Theory of General Relativity predicts analogous ripples in space if large quantities of mass/energy are rapidly accelerated. Because gravity is a comparably weak force only huge events like the collision of two neutron stars or black holes are likely to generate gravitational waves of sufficient intensity to be detected on Earth.

How can we detect gravitational waves?

The effect of gravitational waves is very small and hence difficult to measure. A waves passing through the Earth would be expected to contract space in one dimension and expand it in another. But only by a factor of 1 in 10^21.

Detectors use laser interferometry to measure changes in distance over large distances. The Laser Interferometer Gravitational Observatory (LIGO) in the US uses two vacuum tunnels 4km (2.5miles) long at right angles to each other. A laser bean is split and directed up and back down each tunnel then brought back together. Any small change in the distance of either laser path is revealed by an interference pattern.

Over this distance the detectors are looking for changes in length of less than the diameter of a proton !

In order to remove false readings from local events like seismic activity etc two or more detectors separated by thousands of miles are needed. The LIGO facility has two sites in the US separated by two thousand miles. Add to that the GEO 600 facility in Germany and VIRGO in Italy and we have a good array of detectors, capable of detecting gravitational waves.

What could gravitational waves tell us?

Detection of gravitational waves would be further confirmation of Einstein's Theory of General relativity, and would tell us something about the predicted fundamental particle associated with gravity, the graviton.

We could also learn more about the universe, especially those catastrophic events such as colliding black holes. Perhaps the effects of the big bang itself will be detectable through gravitational waves still propagated through the universe (analogous to the microwave background radiation).

Gravitational waves observatories will potentially tell us more about the universe we live in and the laws that govern it. Unfortunately it will not provide spectacular images that capture the publics imagination, like Hubble does.

How you can help?

You can get involved in this research by signing up for the einstein@home project. Just like the well known SETI@home the idea is to use spare processor capacity on your home PC to analyse data from LIGO / GEO 600 and look for anomalies in the data. The processed data is returned to the project team for further analysis if necessary.

Links
LIGO Homepage
GEO 600 Homepage
Wikipedia Gravitational Waves
Einstein@home