In January, Roxanne loaned me a book called The Fabric of the Cosmos by physicist Brian Greene. It was an engrossing read and although it is written in easy to understand language, it is still a lot to digest in a short time. It took me about six months to get through it reading a chapter or two every few weeks. One of the many things that I found so fascinating was the detailed discussion of the space-time continuum and how it is really like a large sheet of fabric.
When an object like the Earth or the Moon moves in space and time, it is sitting in the fabric of the continuum and causes a dip, not unlike the dip caused by standing on a bed. As the object moves, ripples are created in the fabric not unlike ripples of water that result from a stone being thrown into a pond. The only difference is that these ripples are waves of gravity moving through space and time. As these and other gravity waves travel through space and interact with all objects in their paths, the result is minute compression and expansion of the objects.
We are subject to these waves every day from distant activities occurring throughout the universe, however the changes are so miniscule they can hardly be measured. However, Greene describes a set of devices installed in the United States in different parts of the country that have the precision to measure the infinitesimal changes. The principle behind the LIGO (Laser Interferometer Gravitational-Wave Observatory) devices are interesting and can be read here. The LIGO devices are located in Hanford, WA and Livingston, LA, some 2000 miles apart, in order to filter out any erroneous data that would throw off such a small measurement. Greene goes on to mention that other such devices are being built in Europe.
Scientists at the University of Hanover in Germany have completed the GEO 600 interferometer and it is now working in conjunction with the LIGO devices in the US. They are confident that the world is months away from conclusive measurements of gravity waves which will provide confirmation of Einstein's general theory of relativity.