Re:um (Score 1)

Wait, so you're saying a second is defined in terms of the Earth's rotation? Because, that's not constant, especially in these million year durations that cesium clocks are supposed to only lose a few seconds through. I was under the impression that 'second' was defined in terms of our most precise measurement device, which, up until now, has been cesium:

(taken from merriam-webster): "the base unit of time in the International System of Units that is equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom