The world on time, the same time

A key technology necessary to permit globally synchronized sensors is a well-defined global clock.  There are multiple ways to synchronize clocks (see Time Transfer entry in Wikipedia) where the best uses GPS technology.

While GPS is widely recognized as giving position information, this is only possible because GPS has extremely precise global timing information with the best systems attaining down to 10 ns global accuracy. 

To see how remarkable this is, consider that the speed of light and electromagtic signals is roughly 300 000 km/s or 30 cm pr. ns.  Thus the time delays for radio signals to propagate from one side of a small room to the other side (let’s say a 3 m wide room) is 10 ns, the same amount of time differences it is possible to maintain globally using GPS signals.  I regard this as one of the most remarkable technological feats in many years, yet it is one of the “better kept secrets” of GPS.

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