Gravitational Radiation

Abstract

IN recent years there has been a good deal of controversy about gravitational radiation. Historically, the position is as follows. It was shown quite soon after the publication of the general theory of relativity that the linear approximation to the field equations admits, in certain co-ordinate systems, solutions which have an obvious wave-like character; moreover, it appears from the energy pseudo-tensor that these waves carry energy away from the sources, as in the electromagnetic case. According to this linear theory, waves are emitted by systems of moving masses, and the rate of transmission of energy depends on the rate of change of the moments of inertia of the system¹. Since the field equations (1) are nonlinear, these predictions of the linearized theory have to be treated with caution, and when, in 1938, a method of approximation which took account of the non-linearity was discovered by Einstein, Infeld and Hoffmann², it seemed that the equations of motion of particles moving under their own gravitation contained no terms which corresponded to gravitational radiation. For various reasons this could not be taken as final evidence that gravitational radiation does not exist; but that work and some of its later developments³ cast serious doubts on the validity of the linearized theory.