The atomic clock is so accurate that, had it been running since the Big Bang, 13+ billion years ago, it would only be off of "real" time by four seconds.
Scientists at the Georgia Institute of Technology want to build a nuclear clock that, when asked for comment on the atomic clock's accuracy, shrugs and says, "that's totally b-list."
[The idea would be to use the atomic nucleus like a tuning fork. A nucleus will jump to a higher energy state, then fall back down, and jump up again, only if it is hit with a very specific frequency of light. Tuning a laser so that it prompts these jumps is a way to set its frequency with a phenomenal level of precision. The frequency can then be used like a clock's tick to keep time.
A thorium clock controlled in this way would drift by just 1 second in 200 billion years, the team claims - that is more than 14 times the age of the universe.
So in the face of all this jaw-dropping accuracy, I'm gonna keep saying, "It's, like, mid-afternoon, I think."