Abstract

In Einstein Special Relativity (ESR), each of two co-located observers with a relative motion will differ in their respective views of the time at any remote location. This is the so-called "lack of distant simultaneity" in ESR. However, the Global Positioning System (GPS) is a global network of 24 satellites carrying atomic clocks on board. All of these clocks are simultaneously and continuously synchronized with one another and with ground clocks all over the Earth, although relative velocities are high enough for ESR effects to be strongly significant. This is accomplished by ignoring relative velocities between clocks and synchronizing each clock to the underlying Earth centered inertial frame. But this is exactly the prescription first proposed by Lorentz in an alternate form of the theory of relativity (LSR). LSR still has clock slowing and meter-stick contraction and agrees with all existing experimental tests of special relativity. However, LSR retains a local preferred frame of reference and a ?universal time" standard, and does not require of nature that nothing can propagate faster than light in forward time. The GPS appears to provide the first test capable of distinguishing ESR from LSR, with results favoring the latter.