Time was once simply measured in astronomical terms, with the passage of the sun recording the passage of time. Surprisingly this can be a relatively accurate method of telling the time. Greater accuracy though occurred through the use of mechanical devices, and more latterly electronic devices.
Pendulum clocks though are well known for gaining and losing time, and even electronic clocks are subject to flaws in quartz crystal designs. The truly accurate measuring of time comes about through the use of atomic clocks.
The workings of an atomic clock have, of course, a lot to do with atomic and quantum physics, but the atomic clock is also not that far removed from a pendulum clock. Whilst the pendulum swings, or resonates, once per second, an atom may resonate many thousands of times in that period. The atomic clock works by measuring the resonating frequency of an atom, this frequency being constant. Some people erroneously believe that the atomic clock works by the decay rate of a radioactive atom, which is of course not the case.
Most atomic clocks make use of Caesium 133 atoms, these atoms having a known and constant resonation rate of 9192631770 cycles per second. Thus once that number of cycles has been counted one second has elapsed. No longer is a second simply a fraction of the time for the earth to rotate around its access, but is defined by the number of cycles.
The actual workings of an atomic clock are complex, as you would expect from atomic physics. In essence caesium atoms are put into a vacuum. Lasers are then used to move the atoms through a section where microwaves are at work, and measurements are taken.
The accuracy of an atomic clock is something which many people struggle to get their head around. A caesium clock is accurate to one second every three hundred and sixteen thousand years. Developments of atomic clocks, including hydrogen clocks, should be even more accurate, perhaps to a level of one second every ten million years.
The need for such accuracy may not be immediately evident, and indeed the atomic club doesn’t help to tell the time or date, just the passage of time. This accuracy though is an important aspect of the workings of the internet and things like GPS.
The equipment and science behind making an atomic clock work is complex, but the accuracy available is spectacular.