Atomic clock at NIST (NIST)
What's interesting about atomic clocks?
Measuring distances is something that we have been doing for thousands of years, but precisely measuring time is relatively new. Did you know that the first (sort of) accurate clock wasn't invented until 1656?
Calendars have been around for much longer, but really, do you ever measure your daily appointments in days or, perhaps, milli-seasons? Calendars, as well as sundials -- another early time-system -- are also no good for measuring time between events. A sundial can tell you whether it is 3 o'clock of 4 o'clock, but it can't tell you when 30 seconds have passed, or how long it took you to get to work.
The maker of the first accurate clock was a fascinating and extremely important early enlightenment figure: Christian Huygens (pronunciation
). He designed a pendulum clock. It works because a pendulum always takes the same amount of time to swing back and forth, regardless of how high it swings. (This sounds weird, but it's true.) This clock only lost a few seconds per day, while previous clocks lost a second almost every minute!
Pendulum clocks were the best in the world until the advent of electronic clocks, first built in 1927 at the famous Bell Labs. Quartz clocks work because the crystal structure of quartz crystal is piezoelectric, which means that when you run electricity through it, the crystal itself expands or contracts. This contraction can be linked to a system of gears to drive a clock. Most wristwatches, wall-clocks, alarm clocks, stop watches and kitchen timers use a quartz mechanism.
Quartz clocks vary in accuracy, generally losing between a second per day and a second per week. This is good enough for timing the roast or being at the meeting at 10:30 sharp. Who cares about making something more accurate?
Well, do you like your smartphone and your car GPS? When you set your watch to the "official time", how do you think that's kept accurate? Without the far greater precision of atomic clocks, these things would not work. More precise, futuristic atomic clocks, based on recent advances could have even more amazing applications.
They could measure gravity by the change in the speed of time, allowing the detection of lava, metal, or oil beneath the surface of the earth. They might even be able to test the salinity of water, the shape of the sea floor, or the movement of plates beneath the earth that cause earthquakes.
So how do atomic clocks tick?
Because of quantum mechanics, we know that electrons can only exist in certain very particular states around atoms. They can only be in one energy level and place, or another, but NOT between. When an electron is pushed from a lower energy level to a higher energy level, it generally will only stay there for a certain amount of time before it falls down again. It turns out that the electron stays there for an extremely precise amount of time (.000000000108782775708 seconds for a common cesium atom clock). If you kick the electron up, let it fall down, then immediately kick it back up again, it will go up and down 9,192,631,770 times in one second. Each time the electron falls down, it emits light. The clock works by measuring light waves, and counting one second every time that 9,192,631,770 light waves are seen.
A clock like this only loses a second over something like one million years!
These extremely precise clocks are a fundamental part of our present. The work that won the prize actually makes possible a clock many times more accurate than that.