[time-nuts] What's the time Mr Wolf...

M. Warner Losh imp at bsdimp.com
Thu Oct 30 19:27:54 UTC 2008


In message: <1231b6a80810301141j70c5d1d4oa088e6827c8dccd at mail.gmail.com>
            "Steve Rooke" <sar10538 at gmail.com> writes:
: 2008/10/31 Tom Van Baak <tvb at leapsecond.com>:
: >
: >> 11) Extrapolating this, a point on the Equator would be moving faster
: >> that a point at the poles or even Greenwich, for that matter. So would
: >> a clock at each location move out of synchronisation with each other?
: >
: > Yes, and this also is taken into account. When you get down
: > to measuring absolute frequency at 1e-14 and 1e-15 levels one
: > always takes the local gravitational field into account, which is
: > mostly a function of altitude, but also latitude.
: 
: Guess I've been dumb here but this must mean that not only is time
: affected by relativistic effects but also oscillators as well then.

Yes.  Oscillators will still resonate in their frame of reference at
their normal rate.  If that frame of reference is slightly different
than the defined standard frame of reference, then you need to take
that into account when you are comparing frequency data with others in
a two-way time exchange.  The objective is to tick at the same rate as
the standard frame, when the standard frame is measured from your
frame of reference...

: If gravity affects frequency, can this effect be seen as a daily
: change in the EFC voltage of a GPS locked standard as caused by the
: Moon? Does this also affect the frequency of the atomic standards used
: to measure time? All this must make the measuring of absolute
: frequency to the high orders of accuracy quite complex.

Gravity affects time.  The problem devolves into the classic case of
trying to keep things in sync between different frames of reference.

The tidal effects are much smaller than those from position.  I don't
think that these effects are visible at the 10-14 or 10-15 level, but
since I don't know what level they are visible at, I can't be sure.
I'm sure that someone on this list, maybe as part of their PhD thesis,
has measured this and can report it :-)

Warner



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