Abstract

Of the ten independent classes of experiments testing various aspects of special relativity (SR), half appeared at first to contradict the frame reciprocity prediction of SR in favor of the earlier non-reciprocal relativity theory proposed by Lorentz (LR). However, these were all eventually reconciled by giving new interpretations to SR. and are now cited as experimental corroboration of Sa. One of these apparently contradictory. now reconciled experiments is the Global Positioning System (GPS). GPS shows that clocks in many different reference frames can be simultaneously synchronized and syntonized. and remain that way even as satellite clocks orbit and ground clocks rotate around the Earth?s spin axis. This experimental fact is alien to the spirit of SR. but can be reconciled with it by confining one's attention to the Earth-centered inertial frame. thereby ignoring reciprocity issues. Apparently. only the finding of a natural phenomenon that propagates much faster than light in forward time would unambiguously distinguish between SR and LR in favor of the latter. We present the results of several lines of experimental evidence. both direct and indirect, showing that the speed of gravity is a natural phenomenon of that type. The strongest experiment uses binary pulsar orbits to place a lower limit to the speed of gravity of 20.000,000,000 times the speed of light. Far from upsetting physics, this resolves several current dilemmas, such as explaining how the external gravity fields of binary black holes get updated. and why some recent quantum physics experiments appear to violate the locality condition.