Aspects of General Relativity

Abstract

While the effects of Einstein’s general relativity are not observationally significant for the every day physics of terestial gravity, nor (in almost all cases) for the motion of planets about the sun, nor (as far as we know) for stars within galaxies, nor for galaxies about one another, the theory does give some observed (or observable) corrections to Newtonian theory in suitable circumstances. In addition to the ‘classical’ observed perihelion advance of Mercury (and, to a lesser extent of other planets as well) and the observed bending of light by the sun’s gravitational field, general relativity contributes significantly to the structure of neutron stars, to the stability of stellar models and to dynamical effects in close binary systems owing to energy loss in gravitational radiation. There are also effects which, though small in general relativity, are absent altogether in standard Newtonian theory, such as the slowing down of clocks in a gravitational potential, the time delay in light signals passing near the limb of the sun (both observed effects) and the very existence of energy-carrying gravitational waves (whose observational status is more dubious). Moreover, there are situations in which general relativity, effectively, provides a gross new effect, such as in the structure of black holes (an example of which apparently resides in the X-ray source Cygnus X-1).