Direct Proof of Dark Matter Found! - Page 4

It is completely false that the design of the GPS system ignores relativity theory. Relativistic effects in the GPS system are vitally important. The total difference in the rate of atomic clocks on board a GPS satellite and the reference clock at the USNO amounts to some 38,600 nanoseconds per day. (This is mostly due to a combination of the Sagnac effect for a clock which is moving wrt the GPS receiver, and the relative gravitational time dilation between a stationary clock on the Earth's surface and a stationary clock 20,200 km above the surface, as mentioned in the above quoted paragraph from Ashby's paper; frequency shifts in clocks on the ground wrt UTC due to inhomogeneties in the shape of the Earth also play a role.) In contrast, in order to maintain the accuracies listed above, the GPS system must maintain a timekeeping synchrony within 10 nanoseconds variation per day, indefinitely! The major way in which the 38,600 nanosecond per day discrepancy due to relativistic effects is accounted for is by building into the GPS software used to keep the satellite clocks in synch with each other and to synchronize GPS time with UTC an effective downward frequency shift of 446.47 parts per trillion in the orbiting atomic clocks. In addition to this basic conversion factor, GPS receivers are programmed to take account for the fact that slight eccentricities in the satellite orbits result in tiny periodic changes in the frequency of the orbiting clocks.

On August 22 2006 11:48 maoam wrote:
You're right it does get quite technical, but I'd rather you didn't take my word for it.