Uncertain Principles: Relativity on a Human Scale

Precision clock measurements from NIST, directly observing both gravitational and kinematic time dilation, all without leaving the lab.

You can do this type of experiment with less precise devices, but you’d have to have a more robust apparatus to accumulate the data because you’d need to do a longer experiment. I’ve detailed how commercially available clocks have done the kinematic dilation measurement, though at ~30 m/s rather than 10 m/s, which required an experiment lasting several days. Similarly, one could do an experiment with clocks on different floors of a building over the course of a few weeks and see a gravitational redshift. It’s probably not worth the effort to go out of your way to do so, given the level of confirmation we already have for relativity — GPS works, for example.

The trick here is that these measurements were made in a relatively short period of time, but that’s generally the nature of cutting-edge science like this — it takes a lot of effort to get all the parts to run, and the experiment yields data for a limited time. So Chad is correct in asking whether they really count as “official clocks” — they don’t insofar as timekeeping is concerned. They probably don’t run long enough to really impact a true clock ensemble. The value here is that what’s hard to do today will be easier to do tomorrow, and eventually this (or a competing) kind of technology will become “true” clocks that are more compact and run continuously for extended periods and do have a significant impact on timekeeping.

(I should be listening to similarly-themed talks this week — I was supposed to go the Frequency Control Symposium. But I managed to get sick — not vodka-induced, BTW — as the weekend drew to a close. No way I was getting on a plane at that point. Bleh.)