New Atomic Clock Three Times as Accurate as Old One

Wired:

Both NIST-F2 and the standard it replaces, NIST-F1, are known as cesium-based atomic fountain clocks. This means they determine the length of a second by measuring a natural vibration inside a cesium atom. Within the clock, lasers push together a ball of 10 million cesium atoms and cool them to near absolute zero (which helps reduce noise). The ball is tossed up in a 3-foot chamber, passing through a microwave beam. The microwave beam kicks some of the cesium atoms up into a higher energy state, which causes them to emit light.
The cesium ball is tossed up and down several times, slightly changing the wavelength of the microwave beam each time. Engineers are doing this to search for a particular frequency. They know they’ve found the right one when the microwaves kick up the most of the atoms, producing the maximum amount of light. This is then known to be 9,192,631,770 Hz, a natural resonance frequency of cesium, which defines the length of the second in our modern world.
The previous generation of atomic clock was already quite good at figuring out the length of a second but had a few small sources of error. NIST-F1 operates at room temperature and so the walls of the chamber in which the cesium atom ball is tossed heat up, emitting a small amount of radiation. This interferes with the atoms, causing them to shift ever so slightly in their energy levels. By cooling NIST-F2 with liquid nitrogen, the new timepiece reaches temperatures of – 316 degrees Fahrenheit, virtually eliminating this excess radiation and reducing the shifting 100-fold.
After steady improvement since atomic clocks were invented in the 1950s, researchers think they are reaching the limit of accuracy with the technology. Any clock that is more precise would begin to feel subtle effects explained by Einstein’s theory of relativity. Clocks experience a gravitational warping from massive objects. The Earth, an extremely massive object, causes clocks closer to its surface to run slower relative to those above it.

Way too complex for me, but cool nonetheless. More on keeping time here.