Sunday, October 16, 2011

Neutrinos on the brain-10

C.I.P. points to this article from Technology Review. There is a discussion of a claim by Ronald van Elburg that the motion of GPS satellites is not factored into the time of flight calculations at OPERA.

My reply is that per this note the GPS satellite designers have thought of all of that. A key excerpt:

The concept of coordinate time in a local inertial frame is established for the GPS as follows. In the local Earth-Centered Inertial frame, imagine a network of atomic clocks at rest and synchronized using constancy of c. To each real, moving clock apply corrections to yield a paper clock which then agrees with one of these hypothetical clocks in the underlying inertial frame, with which the moving clock instantaneously coincides. The time resulting from such corrections is then a coordinate time, free from inconsistencies, whose rate is determined by clocks at rest on the earth's rotating geoid.