The most precise clocks in the world will lose only one second every 300 billion years—and someday they might fit in your ...

The length of a second was initially determined astronomically, using Earth's rotation. One second was defined as 1/86,400th ...

at least — is 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of a stationary cesium-133 atom at a temperature of 0K.

The different types of states are separated, and the high energy atoms decay to the low state, emitting light of the same characteristic frequency, which for cesium-133 atoms is precisely ...