system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why was Cesium-133 atom chosen for defining "1 second" under Standard International?

I remember years ago in high school my physics teacher explained to us that Standard International defines 1 second as "the time needed for Cesium-133 to vibrate 9.192.631.770 times". Is there any particular reason why Cesium-133 was the element chosen for this purpose?

Edit: wow, my first silver award! Thank you!
gpt
Accuracy & consistency are the most important things for SI determination. Caesium has a very, very high resonant frequency.

A quartz clock is accurate to something like 1 second in a couple of years.

A caesium atomic clock is accurate to something like 1 second in a million years.