At 06:25 PM 2/23/2010, David C. Partridge wrote...
No they cannot be - yet. At the point where (e.g.) the second is
re-defined
in terms of the aluminium quantum clock, then the aluminium quantum
clocks
are then by definition the primary standards of time, and all the Cs
clocks
are now secondary standards as the second is no longer defined in
terms of
the Cs beam clock.
I disagree. A Cs clock is not a primary because it uses Cs, but because
it's the pragmatic state-of-the-art. A Cs clock which determines time
based on the definition simply doesn't exist, it meets only 1 of 3
criteria. If a demonstrably more stable clock, using any technology,
can be shown to exist, it too qualifies as a primary standard. Better
is better.
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