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The changing times: from sundial to quantum clock



The American National Institute of Standards and Technology has an atomic clock. It only gains or loses a second once every 300 million years. That’s an immense improvement from the sundial, from the pendulum clock, and from the chronometer. Can time be even more precise? Scientists think so, with the advancement of a quantum clock.

The sundial, now more of a garden ornament than a time teller, uses a vertical pointer that casts a shadow on a flat surface to indicate the time of day. It was the earliest known time keeping device, but the disadvantage was that the shadow could not be seen on a cloudy day, or at night. And it was not portable.


The pendulum clock, the invention of Dutchman Christiaan Huygens (1629-1695), measured time both day and night. It was quite reliable but the pendulum swung faster at lower altitudes and at the Earth’s North and South Pole. Hence gravity affected the precision of the time recorded, and the precision of its parts. Again, it was not portable, and it was most inaccurate at sea—at a time when explorers were navigating the oceans.


To enable sailors to calculate longitude, Englishman John Harrison (1693-1776) designed and produced a chronometer in 1730. It was an accurate timepiece that could determine longitude to within half a degree. It kept time to within 0.8 seconds per day—and it was portable. This is the version of the watch that is very familiar to all of us.


Established in 1901 the National Institute of Standards and Technology created the first atomic clock in 1949. It determined time by measuring the duration of atomic processes. In 1967 NIST determined that 9.2 billion oscillations of microwave radiation emanating from a system of cesium atoms is the definition of one second. It is accurate to within one second every 300 million years.

Now scientists are proposing a quantum clock (according to a study published in Nature Physics). It is actually a network of atomic clocks already on global satellites and they will be stationed at locations around the Earth (in laboratories). Each of them would instantly relay its time to one central node, which would then average the times to give one definitive time. This quantum clock would be called a superclock. It is expected to be accurate to within one second every 13.8 billion years.

Scientists maintain that such a clock would enable them to accurately measure continental shifts (shifting land) and thus natural disasters, such as earthquakes and tsunamis.


Discover, December 2014, www.discovermagazine.com



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