Although Gravitational Signals from Supernovae and Black Holes

I i",y rctating binary ccvnc acd thr rio:.as arigir,al!y motivated by the chalnian "actioil a t a distailce." li,emaiklent evtints occuiring in quasars a i d lengt. of measuring ihe Rie~nann curvaably, the theory, withoui an arbitrary I galactic nuclei, has opened a new era lure tensor, an abstract mathematical parameter, made predictions of deparof general-relativity physics. In the object that, we will soon see, plays a tures from Newtonian gravity that 1960's nearly all workers in the field central role in Einstein's geometrical were subsequently verified. considered the detection of gravitatheory of gravity. Weber pursued his I t is ironic, however, that the part of I tional radiation "exceedingly unlikegoal in spite of widespread skepticism, Einstein's theory that would seem i ly."l Froin this pessimistic estimate although he acknowledges strong enmost essential to its field nature, the the balance of opinion has shifted to couragement from such supporters as prediction of gravitational radiation, the optimistic view that gravitational P. A. M. Dirac, Freeman J. Dyson, J. was the farthest from direct experiI radiation, a crucial prediction of EinRobert Oppenheimer and John A. mental verification; furthermore, there stein's general theory of relativity, is Wheeler. ensued until quite recently debate now within reach of current experiWeber's experiment sets an imporamong workers in the field as to the mental techniques. tant upper bound a t 1660 Hz, the resovery existence of gravitational radianant frequency of his detector. Prestion within the structure of the theory. Pioneering work ent detectors are capable of measuring The issue of the theoretical existence of Joseph Weber, the pioneer in the relative displacements of less than gravitational waves concerns us only in field of gravitational wave detection, 10-l5 cm (two orders of magnitude less its resolution. Relativists have come has been reporting coincident events in than nuclear diameters) between the to realize that the proper measure of his detectors since 1969. An internaends of a bar meters long. Improvethe existence of gravitational waves is tional effort to duplicate Weber's exments during the next decade should the Riemann curvature, R a b t d , a fourperiment has so far failed to confirm allow measurement of strains as small indexed tensor, which describes the his results, although Weber continues as & l / l = This is a good opporlocal tidal forces. Previously, such to measure coincidences. Nonetheless, tunity to examine the prospects of gratechnical problems as nonlinearity, gravitational-wave detectors are imvitational-wave detection, putting into lack of local gravitational energy densiproving dramatically and may soon be perspective the theoretical basis, possity, and the general coordinate transforsensitive enough to detect gravitational ble astrophysical sources, and the state mation group admitted by general rela. radiation from known astrophysical of the experimental art of gravitativity obscured the meaning of gravita-