The confrontation between general relativity and experiment

Abstract

Abstract. We review the experimental evidence for Einstein's general relativity. A variety of high precision null experiments confirm the Einstein Equivalence Principle, which underlies the concept that gravitation is synonymous with spacetime geometry, and must be described by a metric theory. Solar system experiments that test the weak-field, post-Newtonian limit of metric theories strongly favor general relativity. Binary pulsars test gravitational-wave damping and aspects of strong-field general relativity. During the coming decades, tests of general relativity in new regimes may be possible. Laser interferometric gravitational-wave observatories on Earth and in space may provide new tests via precise measurements of the properties of gravitational waves. Future efforts using X-ray, infrared, gamma-ray and gravitational-wave astronomy may one day test general relativity in the strong-field regime near black holes and neutron stars. Keywords. gravitation, gravitational waves, relativitySince the late 1960s, when it was frequently said that "the field of general relativity is a theorist's paradise and an experimentalist's purgatory" the field of gravitational physics has been completely transformed, and today experiment is a central, and in some ways dominant component. The breadth of current experiments, ranging from tests of classic general relativistic effects, to searches for short-range violations of the inverse-square law, to a space experiment to measure the relativistic precession of gyroscopes, attest to the ongoing vigor of experimental gravitation.The great progress in testing general relativity during the latter part of the 20th century featured three main themes:• The use of advanced technology. This included the high-precision technology associated with atomic clocks, laser and radar ranging, cryogenics, and delicate laboratory sensors, as well as access to space.• The development of general theoretical frameworks. These frameworks allowed one to think beyond the narrow confines of general relativity itself, to analyse broad classes of theories, to propose new experimental tests and to interpret the tests in an unbiased manner.• The synergy between theory and experiment. To illustrate this, one needs only to note that the LIGO-Virgo Scientific Collaboration, engaged in one of the most important general relativity investigations -the detection of gravitational radiation -consists of over 700 scientists. This is big science, reminiscent of high-energy physics, not general relativity! Today, because of its elegance and simplicity, and because of its empirical success, general relativity has become the foundation for our understanding of the gravitational interaction. Yet modern developments in particle theory suggest that it is probably not the entire story, and that modifications of the basic theory may be required at some level.