Tiny Ticks

Cesium Clock

 In our everyday real world we view change as an analog process. That is, it occurs continuously. Change is unlike a of chain with individual links forming the entirety chain rather than like a cable with no individual lengths. Change is not as a series of events happening end to end, one after the other, without breaks as in a chain. Analog change is continuous event from beginning to end. 

But in the quantum world, change is not continuous but occurs as individual events like the links in a chain jointed together to form a whole. Quantum change occurs in a connected series discrete chunks. And these chunks can be used as the "ticks" in a clock. 

Today the clock of last resort is an atomic clock which use the quantum "ticks" of a quantum event in that occurs in Cesium -133 atoms (the microwave electromagnetic radiation emitted or absorbed by the quantum transition (energy change) of  the ground state of Cesium-133 atoms). We define a total of  9,192,631,770 changes of the ground state of the Cesium-133 atom as 1 second. So it is that our smallest measure of change is one tick (1/9,192,631,770) of the Cesium-133 atomic clock. All other changes we observe and measure are measured relative to the "ticks" of this clock.

So how small is one "tick"? Well, the Cesium-133 atom clock ticks about 795 trillion "ticks" every time the earth makes a complete rotation ("day"). If you were sitting on the equator you would travel about  25 thousand  miles in a circle around the axis of the earth every rotation. And so it is that you would travel about 2 thousandths (0.002) of an inch per "click" of the atomic clock. That amounts a change in position that is equal to the thickness of two human hairs in 25,000 miles.

Yes, we can count the number of ticks. And, yes, we do use atomic clocks and their tiny ticks in real world applications. A familiar one is their use in Global Position Satellites (GPS) so that your cell phone can accurately tell you where in the whole wide world you are within in a few feet.