NavList:

David Iwancio, you wrote:
"I would have thought that multi-billion-dollar tech companies could have simply bought some laser gyroscopes and measured UT1 directly and autonomously."

They neither need nor want UT1. And really, that's the whole point. They want atomic time going forward since it is completely deterministic. At present UTC is based on atomic time but with occasional seconds added in (and potentially removed in the event of a "negative" leap second) in order to keep the UTC standard relatively close to UT1. And these "leap seconds" are not deterministic. They depend on the variations of the Earth's rotation rate, which while highly stable by standards that existed a century ago, now seem as variable as a light afternoon breeze. So astronomers and the keepers of time standards have to throw in a leap second now and then to keep the difference between UT1 and UTC below 0.9 seconds. This is by definition of UTC dating back half a century ago. But why do we care? Why worry if UT1 gets three seconds, or a minute, or 15 minutes, or an hour or more out of step with UT1?

You wrote:
"We just recently abandoned the use of a physical, manufactured artifact to define the kilogram, so why does it feel like we're doubling down on using one to define our epoch/timestamps?"

I think you have got it backwards. Dropping leap seconds implies that UTC becomes a pure count of seconds. This is as near as possible to "true time", the underlying time variable in the laws of Nature, as we can possibly get. The "artifact" --in this case the great rotating mass of the Earth itself-- is removed from the picture. By dropping leap seconds, UTC becomes an echo of atomic time with no further connection to the orientation of the Earth.

Frank Reed