[time-nuts] NPR Story I heard this morning

Peter Monta pmonta at gmail.com
Mon Nov 3 14:54:41 EST 2014

Chris Albertson writes:

> But you are right, no two clocks will ever agree at that level because they
> will experience different gravitational fields.  At this level the reason
> to have a clock is no longer to tell time.  It is to measure the
> gravitational field.

I have a question about that.  If I understand correctly, recent IAU
resolutions have decoupled the definition of the SI second from the
terrestrial geoid, which is too fuzzy to be used for a definition.  Instead
the geoid potential is held fixed by (or defined by) a constant.  Potential
with respect to what exactly?  "At infinity" is all very well, but there
are local gravity sources (solar, even galactic) that would seem to
complicate any operational realization of this definition.

Sorry if this is a bit off-topic.  I'd like a simple, clear explanation for
the layman that drills down on exactly how the current definitional scheme
can be realized to arbitrary precision.  For example, assume that we must
go off-earth at some point to get a better timescale.  How fuzzy is the
solar potential ("soloid")?


More information about the time-nuts mailing list