The second is a date, something we agree on: This is a second. “However, this designation ran into some problems with our modern technology,” Shire said.
In fact, you could start by saying, ‘What is today? From noon to noon, that’s 24 hours, and then you divide that into minutes and seconds. So you can define the second as the thousandth part of a whole day. The problem is, because our measurements are now very good I was able to see for a long time that the length of the day is not constant. Spin The Earth is actually a little slower all the time, after all, we’re slowing down because of the tides and the moon.”
“It’s very simple,” admits Scheire, “but the result would be that if you stick to that definition, a second in a hundred or a thousand years would be longer than a second today.” And you don’t really want that, because in physics to be able to think of a second as the time of the decay of an atom.”
“There are a lot of physical processes that need that second, without changing over time, so they said in the 1950s, ‘Okay, redefine, now we’re going to look at the vibrations from the outgoing radiation. Cesium can come in as an atom.” This thing vibrates, has a frequency of about 9 billion times a second, and it’s, as far as we know, pretty much constant across the universe and all of time, so we’re going to define a second as 9 billion times. Some of those vibrations are radiation from Cesium atom.”
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