[time-nuts] Question re neutrinos and GPS

Tom Van Baak tvb at LeapSecond.com
Sun Jan 8 15:11:24 UTC 2012


> what about swapping the Cs clocks between CERN and LNGS without re-
> synchronizing them, and repeating the neutrino test?
> 
> Antonio I8IOV

Right, typically when you perform a traveling clock experiment
you don't touch the clocks -- you don't need to synchronize or
resynchronize anything. The key point is the difference in time
from A to B, or A to B to A. This is accomplished with a time
interval counter and you do the subtraction with a calculator.

Imagine that you have two Rb in your house and wish to compare
their times. If they are too far apart to use a long cable, one trick
is to use a "traveling" quartz clock and TIC. You measure Rb1-Qz
and then walk to the other clock in order to measure Rb2-Qz.

Ignoring effects like drift in quartz or counter, the time of the
quartz drops out of the calculation of Rb2-Rb1. Make sense?

So there's no mathematical requirement for synchronization of
the traveling clock. And there's also a practical reason why you
don't precisely synchronize or resynchronize -- most Cs have
a 100 ns granularity on their 1PPS sync input.

/tvb





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