The clock is ticking

Clocks slay time... time is dead as long as it is being clicked off by little wheels; only when the clock stops does time come to life. - William Faulkner

In August 1967, a signal from the heavens was detected. It appeared to come from a radio source in outer space, and it was in the form of extremely regular radio pulses. Their period, that is the time difference between two consecutive pulses, was measured to be 1.3373011512 second. To quote the period to an accuracy of 10 decimal places was unprecedented. Were these signals from an advanced extra-terrestrial civilization?

Science fiction buffs were to be disappointed. The signals were from a pulsar, christened with the name "CP 1919" - CP standing for "Cambridge Pulsar" and 1919 representing its coordinates in the sky (sidereal time 19h 19m). Since 1967, many more pulsars have been detected, but we still do not have a clear picture of exactly how they work, although we know that they must be neutron stars. Perhaps the most accepted model of a pulsar was proposed by astrophysicist Tommy Gold. It is of a spinning neutron star, with the pulse period being the period of rotation of the star about its axis. You see, a neutron star is surrounded by an "atmosphere" of charged particles, and as it spins so does the atmosphere, carried along by the star's gravitational pull. These particles may move at close to speed of light, and may generate electromagnetic waves in the presence of magnetic fields. However, with the passage of time, a neutron star's spin slows down, causing its pulse period to increase ... but that takes a long time.

On Earth, we define universal time in terms of the caesium clock, where one second is defined as the time it takes for 9192631770 cycles of radiation emitted during the transition two specified energy levels of a caesium-133 atom. The time intervals of such transitions are not always the same but, by averaging over several such transitions, we can arrive at a steady period.

How does the accuracy of "pulsar clock" measure up against a caesium clock? To measure the stability of clocks, we use the Allan variance. Such measurements show that, over short time scales (e.g. a month), the pulsar's period is not as stable, but over longer time scales (years), the pulsar is much more stable.

The late great Carl Sagan wrote in his book "Billions and Billions":
Our civilization runs by burning the remains of humble creatures who inhabited the Earth hundreds of millions of years before the first humans came on the scene. Like some ghastly cannibal cult, we subsist on the dead bodies of our ancestors and distant relatives.
Our civilization also dances to the tune of a few atoms changing state but one day, the machinations of our well-oiled societies will be be dictated to by faded stars in their death throes.
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