On Wed, 3 Jan 2007, Magnus Danielson wrote:
>
> Assuming you have corrected for another gravitational field, yes. The
> current SI second indirectly assumes a certain gravitational force, we
> is assumed to be "at sea level" whatever level that is.
Wrong. The SI second is independent of your reference frame, and is
defined according to Einstein's principle of equivalence. What *does*
depend on the gravitational potential at the geoid is TAI (and TT), since
a timescale (unlike a fundamental unit) is relative to a reference frame.
> We still depend on geophysics to some degree.
Note that the standard relativistic transformations between TT, TCG, and
TCB is (since 2000) independent of the geoid. So although the realization
of these timescales is dependent on geophysics (because the atomic clocks
they are ultimately based on are sited on the planet) the mathematical
models try to avoid it.
Tony.
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Received on Wed Jan 03 2007 - 09:55:31 PST