General Relativity and Gravitation, Vol. 7, No. 4 (1976), pp. 333-337 A New Test of General Relativity*] ROBERT V. WAGONER Institute of TheoreticaI Physics, Department of Physics, Stanford University, Stanford, California 94305 Abstract The emission of gravitational radiation by the recently discovered binary pulsar system will cause its orbital period P to decrease at a rate which can now be predicted to be P-ldP/dt = - (3 +- 2) X 10.9 yr -1 if the only orbital perturbations are of general-relativisticorigin. It is shown that other sources of period change are probably less important. The accuracy of this prediction as well as the possibility of its verification will improve greatly over the next few years. This is the Ftrst observation that can test general relativity beyond the post-Newtonian approximation. In the study of gravitation, the struggle for each new experimental result is arduous, but the rewards are great, since we have so little evidence concerning the relativistic properties of the gravitational interaction. In the past, these ex- periments have been carried out in the laboratory of the solar system, because only there have we been able to disentangle the gravitational from the astro- physical effects. However, the recent discovery [1] of a pulsar (PSR 1913+16) in a binary system has provided us with another system relatively free of astro- physical complications. It is the purpose of this essay to show that this system may make possible a new test of general relativity, one that is unique in three ways. First, it is the only new test that has a chance of being accurately carried out on this system. Second, it is the first test of general relativity that probes its structure beyond the first post-Newtonian level of approximation. Third, it is based upon the effects of gravitational radiation. *Work supported in part by National Science Foundation under grant No. MPS 74-15524. ~This essay received the fifth award from the Gravity Research Foundation for 1975 (Editor). 333 9 1976 Plenum Publishing Corporation, 227 West I7th Street, New York, N.Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without the written permission of the publisher.