Cesium atomic clock: 10 GHz, one part in 10^10

I've got one in my office, I've got one in my bedroom, I've got one in my kitchen. You can buy them. Most of you in this room have an atomic clock right now on your person. Quartz and cesium — well, cesium is correct. The atomic clock is based on cesium. Before that we had quartz, and we were looking at the vibration of quartz, and we could separate time into millionths of a second with a quartz crystal oscillator. The cesium atom vibrates at 10 gigahertz, so we can separate time into ten billionths of a second. The atomic clock for time — cesium, Cs, not cerium, cesium — is 10 gigahertz, which means one part in 10 to the 10th seconds is the accuracy of our measuring time, because of the research that was done up the road here in Cambridge.