Hey @lemouth, thanks for another interesting read!
But this does not tell us what a second is. For that, please hold on for a second. I know: I ate a clown today and here is the proof.
Lol!
After being cooled down, the atom are thrown upward, at an altitude of about a meter, and they then fall by gravity. The setup is called an atomic fountain.
I was wondering why they do this but then you got me!
They have managed in this way to improve the precision of the clocks by a factor of about 100. In other words, a leap second has to be inserted once every 300 million years!
Just wow!
By the way, apart from experiments conducted by physicists, are there any other applications that would demand precision of measured time of up to 16 to 18 digits? 10^(-18) sec is one insanely small time interval! Just wondering!
Have a good day!
GPS synchronization relies on atomic fountains. Except this, we need such a precision to test general relativity to its deepest details (some reference to @alexander.alexis). See fo instance the Pharao project.