Scientist have built a pair of clocks that keep time with staggering accuracy using the vibrations of atoms trapped in laser beams. Their agreement was so good that if they had started running when the universe was born, they would now be out of time with each other by less than a second.
The capacity to keep accurate time has been one of the most important technological quests in human history. In fact, tens of thousands of sailors owe their lives to the marine chronometer that provided accurate measurements of time at sea.
The quest to track time so precisely that a clock would lose one second in 16 billion years—three times the age of the sun—however, might come across as merely perverse. The caesium atomic clocks we have used for the last 60 years have inaccuracies of a second every 30 million years, small enough that if you were relying on one built by dinosaurs, no one would notice your tardiness for coffee.
However, exceptionally precise time measurements are important to GPS and communications networks. Professor Hidetoshi Katori of the University of Tokyo says the work takes us close to the point where we can use comparisons between clocks to measure tiny relativistic effects caused by changes in gravity. This would allow us to observe geological movements that could help us track, and maybe one day predict, earthquakes or find variations in the Earth's gravitational field that could be used to locate mineral resources.
Announcing his success in Nature Photonics, Katori says the major source of uncertainty in existing high-precision clocks has been the influence of blackbody radiation, known as the Dick Effect and once thought to set a limit on how perfectly clocks could keep time.
Katori's optical lattice clocks operate by trapping strontium atoms in a grid of lasers. The clocks rely on the fact that the wavelength of laser light used does not disturb the atoms, leaving them to vibrate at their natural frequency. Several teams have been working on similar technologies, some choosing other elements such as ytterbium. The combination of the laser grid and cooling to -180°C has allowed Katori to not only produce such extraordinary timing precision, but to keep it going for a month where other experiments only lasted hours.
This is not the final word in chronological precision, however. Katori measured disagreements between the two clocks as 7.2 x 10-18, and in some trials to 2 x 10-18, but calls “the low 10-18 level” to be his goal. The work may even allow us to redefine time, with the research team issuing a statement saying, "Through improved precision, we hold high hopes for accelerated discussions on redefinition of the 'second'."
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