Another interesting occurrence that has yet to be directly detected is the phenomenon known as gravitational waves. As we know from Einstein’s general theory of relativity, we live in a four dimensional universe called space-time and the fabric of this universe, the very dimensions of space-time itself, is curved by the presence of matter. For more on general relativity and space time see What is Gravity Page 7.
According to current theory, gravitational waves are vibrations that travel through space time. Think of them as similar to ripples on the surface of a pond if you like. What causes these ripples you ask? Technically, the movement of any matter can create them. However, because space-time is such an incredibly rigid medium through which to transmit waves (it is millions of times more difficult to bend than solid steel for example) it takes a very powerful occurrence to actually generate real gravitational waves. Such large scale events could include super novas or even the mutual orbits of binary pulsars. In fact, through the latter we have already obtained indirect evidence of the existence of gravity waves.
Binary pulsars are two neutron stars which orbit around each other at rates sometimes approaching one revolution per day. Recently, scientists have observed such a system wherein the stars’ orbits are quickly becoming smaller and smaller, a sign that they are losing energy. But the only way we know of to explain such a rapid loss of energy is that the stars are creating gravitational waves.
Despite these types of clues however, astronomers have not actually been able to detect gravitational waves thus far. This is probably because our current technology is simply not sensitive enough. Currently the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (Caltech) are constructing a huge, two-part gravitational telescope known as the Laser Interferometer Gravitational-wave Observatory (LIGO) with which they hope to be able to detect these elusive waves.
