The Global Positioning System and the Lorentz Transformation

The Global Positioning System has been hailed as one of the great triumphs of relativity theory. It is based on the principle that the rates of atomic clocks are affected in a well-defined manner by changes in their relative velocity to the Earth and their position in a gravitational field. It also is consistent with the modern definition of the meter as the distance light travels in free space in c-1 seconds. Two experiments carried out on GPS satellites are considered that provide further crucial tests of Einstein's special theory of relativity (STR), in particular of its prediction of the non-simultaneity of physical events and Fitzgerald-Lorentz contraction (FLC) of objects in relative motion to the observer. Each of them leads to a contradiction of the Lorentz space-time transformation that is generally considered to be the fundamental basis of STR. The results are consistent with the relativistic velocity transformation, however, and also do not stand in contradiction to the Lorentz invariance of the electromagnetic field, both of which have a clear experimental basis in contrast to the FLC and non-simultaneity. They also do not violate either of Einstein's two fundamental postulates, Galileo's relativity principle and the constancy of the speed of light in free space. Based on these arguments, it is concluded that the laws of physics are indeed the same in all inertial systems, but that the fundamental units in which they are expressed vary with both the state of motion of the observer and his position in a gravitational field.