100 Years of Relativity Space-Time Structure: Einstein and Beyond ...

CHAPTER 8WAS EINSTEIN RIGHT? TESTING RELATIVITYAT THE CENTENARYCLIFFORD M. WILLDepartment of Physics and McDonnell Center for the Space Sciences,Washington University, St. Louis, MO 63130, USAcmw@wuphys.wustl.eduWe review the experimental evidence for Einstein’s special and generalrelativity. A variety of high precision null experiments verify the weakequivalence principle and local Lorentz invariance, while gravitationalredshift and other clock experiments support local position invariance.Together these results confirm the Einstein Equivalence Principle whichunderlies the concept that gravitation is synonymous with spacetimegeometry, and must be described by a metric theory. Solar system experimentsthat test the weak-field, post-Newtonian limit of metric theoriesstrongly favor general relativity. The Binary Pulsar provides testsof gravitational-wave damping and of strong-field general relativity. Recentlydiscovered binary pulsar systems may provide additional tests.Future and ongoing experiments, such as the Gravity Probe B GyroscopeExperiment, satellite tests of the Equivalence principle, and tests of gravityat short distance to look for extra spatial dimensions could constrainextensions of general relativity. Laser interferometric gravitational-waveobservatories on Earth and in space may provide new tests of gravitationaltheory via detailed measurements of the properties of gravitationalwaves.1. IntroductionWhen I was a first-term graduate student some 36 years ago, it was saidthat the field of general relativity is “a theorist’s paradise and an experimentalist’spurgatory”. To be sure, there were some experiments: IrwinShapiro, then at MIT, had just measured the relativistic retardation ofradar waves passing the Sun (an effect that now bears his name), RobertDicke of Princeton was claiming that the Sun was flattened in an amountthat would mess up general relativity’s success with Mercury’s perihelion205