[ntp:questions] Leap second to be introduced in June

William Unruh unruh at invalid.ca
Mon Jan 26 20:48:01 UTC 2015

On 2015-01-26, David Woolley <david at ex.djwhome.demon.invalid> wrote:
> On 26/01/15 17:11, William Unruh wrote:
>>> physical principle ( the frequency of oscillation of a cesium atom in a
>                                           XXXXXXXXXXXXXX
>>> >certain transition) and the rotation of the earth. It used to be defined
>>                           ^not
>>> >
> It's a quantum spin flip.  There is no physical oscillation. Not that 
> that really changes anything about UTC or TAI.

Tell that to the electromagnetic wave that comes out of the atom. The
energy of that spin flip corresponds directly to a frequency via
Planck's constant. And yes, an actual frequency of oscillation of the EM

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