21 June 2010

The Second

Have you ever wondered who decided how long one second is... Ever wonder if there is an actual definition of "one second?"

I didn't think so.

But there IS a definition. It is, after all, the fundamental unit of time and the one science uses to measure everything. In the good old days, when women covered their knees and listened to their husbands, scientists defined the "second" in terms of the time it took for the earth to rotate once on its axis, commonly known as "a day."

1 hour = 1/24 day
1 minute = 1/60 hour
1 second = 1/60 minute

So a second was 1/86,400th of a day. Unfortunately, the length of a day changes over time so this definition was not precise enough. So in 1967 a group calling itself the General Conference on Weights and Measures (also the name of my new band) came up with this jaw-droppingly precise new definition of a "second," the one which is used by the world today:

The duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of cesium-133 atoms in their ground state undisturbed by external fields.

Aaah, that clears it up!


Mark said...

Isaac Asimov wrote about a hundred columns about the science of measurement. Seconds were a vague for a very long time but even days weren't exact until fairly recently.

Wes said...

I'm just glad they chose Cesium-133, because it's stable. Can you imagine how wacky our clocks would be if they'd picked Cesium-132 or -134? Or, God help us, -144??

Madness, I says. Madness!