Gravitational radiation

Abstract

If we ask what characterizes radiation, our answers might include the transmission of energy and information through space, or the existence of a wave equation which some quantity satisfies. These aspects are, of course, related, in that there is a characteristic speed of transmission which is determined by the wave equation. In Newtonian gravitational theory energy (and information) is transmitted via the gravitational field which is determined by the gravitational potential V. In empty space V satisfies ∇²V = 0, which is not a wave equation, but might be regarded as the limit of a wave equation in which the characteristic speed of transmission tends to infinity. Put another way, gravitational effects are, according to Newton’s theory, transmitted instantaneously, which is thoroughly unsatisfactory from the relativistic point of view. Moreover, with an infinite speed of transmission it is impossible to associate a wavelength with a given frequency of oscillation.