[time-nuts] Question re neutrinos and GPS

[Bill Hawkins]

Tom,

I had to look up "traveling clock synchronization" to get a
better understanding, and found this link:

http://www.newtonphysics.on.ca/einstein/chapter9.html

The idea that Qz (time on the quartz clock, no?) drops out in
the subtraction seems to me to require Qz to be invariant.
That seems beyond the capability of quartz at the required
error of one microsecond during the many hours that it will
take to transport Q between CERN and LNGS. Plenty of time
for cracks to propagate or chips fall off.

Why do you say we can ignore such effects?

Thanks for any enlightenment.

Bill Hawkins


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Sunday, January 08, 2012 9:11 AM
To: iovane at inwind.it
Cc: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Question re neutrinos and GPS

> 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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