Re: What is so sacred about 9,192,631,770?
The idea is to stop using physical items that can chance shape, size, density, etc. and have to be adjusted for the ambient conditions at the time of measurement. Seconds used to be defined as a 1/86,400th of a mean solar day. But of course, the Earth is very much a physical item that changes based on ambient. Notice the use of "mean" in the old definition of second. More importantly, with a slowing rotation, anything that uses second as a unit will change over time. That means that you would have to constantly update measurements of fundamental phenomena, like the speed of light. Today it might be 299,792,458 meters/second, but using an Earth-derived second means it might be 299,792,458.5 meters/second in a couple years. Defining seconds by the number of vibrations of a Cesium atom means it's tied to a fundamental property of nature, though one that can be still influenced by external forces, like local gravity.
Even today the margin of error for an atomic clock is enough to add uncertainty to the true speed of light, and we have other. Adding a leap second for the sake of coordinating time is purely for those of us Earth-bound souls. And since most of us only measure time down to the second (with some people going to ms), that resolution is good enough. But perhaps we need to stop thinking about time from an earth-derived value.