Physics of Relativistic Objects in Compact Binaries: from Birth to Coalescence

Book Preface

A very attractive feature of the theory of general relativity is that it is a perfect example of a “falsifiable” theory: no tunable parameter is present in the theory and therefore even a single experiment incompatible with a prediction of the theory would immediately lead to its inevitable rejection, at least in the physical regime of application of the aforementioned experiment. This achievements of the human intellect ever, and motivates a wealth of efforts in designing and implementing tests aimed at the falsification of the theory.

The first historical test on the theory has been the deflection of light grazing the solar surface (Eddington 1919): the compatibility of the theory with this first experiment together with its ability to explain the magnitude of the perihelion advance of Mercury contributed strongly to boost acceptance and worldwide knowledge. However, technological limitations prevented physicists from setting up more constraining tests for several decades after the formulation of the theory. In fact, a relevant problem with experimental general relativity is that the predicted deviations from the Newtonian theory of gravity are very small when the experiments are carried out in terrestrial laboratories. A rough estimate of the expected magnitude of general relativity corrections can be drawn from a comparison between the classical gravitational potential energy Egrav ∼ −GM2/R of a body of mass M and radius R and the rest mass energy of the same body, Erest = Mc2 (G being the gravitational constant and c the speed of light in vacuum). On Earth, the dimensionless ratio = |Egrav/Erest| is of only ∼ 10−10 and, as a consequence, very sensitive experimental apparatuses are necessary for detecting the tiny discrepancies resulting from the application of Einstein’s theory with respect to the predictions of Newtonian gravity.