Laser Interferometer Gravitational Wave Detectors

Abstract

In the last few years an increasing effort has gone into the development of gravitational radiation detectors based on laser interferometers and to introduce the subject it might be useful first to consider some of the reasons for attempting to detect gravitational radiation at all. One objective is clearly just to observe the radiation and confirm its existence, and thus provide a check of one of the more interesting predictions of general relativity. The beautiful observations of changes in orbital period of the binary pulsar are of course giving good evidence for loss of energy corresponding to that expected by emission of gravitational radiation from the system. However, it would be very significant to detect the radiation directly. And if more than mere detection is achievable, many of the predicted properties of the radiation might be experimentally checked. For example, simultaneous observation of a single gravitational wave burst by a number of wide-band gravity wave detectors at widely separated locations on the earth could give information on the velocity of the radiation, and possibly on polarization properties. If a gravitational wave pulse could be associated with another observed astronomical event, such as a supernova outburst, more precise information on the velocity could be obtained. Other possibilities arise if continuous gravitational waves, such as from a pulsar or a fast binary system, are detected and observed for an extended period. Measurements of periodic changes in amplitude of signal recorded by a detector rotating with the earth, and of changes in its phase due to the earth’s orbital motion, could give fairly precise data on polarization and on velocity of propagation. Such experiments might be regarded as analogous to the discovery and experimental study of a new predicted particle in high energy particle physics. And although one may think one knows what the results will be, the experiments are still extremely important.