What the world’s most accurate clock can tell us about Earth and the cosmos

It would take 15 billion years for the clock that occupies Jun Ye’s basement lab at the University of Colorado to waste a second, roughly how long the universe has been around.

For this invention, the Chinese-American scientist, along with Hidetoshi Katori from Japan, will share $ 3 million as co-winners of the 2022 Breakthrough Prize in Fundamental Physics.

Working independently, the two developed techniques using lasers to trap and cool atoms, then harness their vibrations to drive what are known as “optical lattice clocks,” the most precise timing parts ever built.

In comparison, today’s atomic clocks lose one second every 100 million years.

But what do we gain from greater precision?

“It really is an instrument for you to probe the basic fabric of space-time in the universe,” Ye told AFP.

In Ye’s lab, researchers have shown that time passes more slowly when the clock is brought a few inches closer to the ground, in line with Einstein’s predictions of relativity.

Applied to current technology, these clocks could improve the accuracy of GPS navigation by a factor of a thousand, or help make an unmanned space plane land smoothly on Mars.

A brief history of time

Improving the precision and accuracy of timekeeping has been a goal since the ancient sundials made by the Egyptians and Chinese.

A key breakthrough came with the invention of the pendulum clock in 1656, which relies on an oscillating weight to keep time, and a few decades later, stopwatches were accurate enough to determine a ship’s longitude in sea.

The beginning of the 20th century saw the advent of quartz clocks, which, when shaken by electricity, resonate at very specific, high frequencies or at a number of tics per second.

Quartz clocks are ubiquitous in modern electronics, but are still somewhat sensitive to variations caused by the manufacturing process or conditions such as temperature.

The next big leap in timekeeping came to harness the movements of energized atoms to develop atomic clocks, which are immune to the effects of such environmental variations.

Physicists know that a single, very high frequency will cause particles called electrons orbiting the nucleus of a specific type of atom to pass into a higher energy state, finding an orbit further away from the nucleus.

Atomic clocks generate the approximate frequency that causes atoms of the element cesium to switch to this higher energy state.

Then a detector counts the number of these energized atoms, adjusting the frequency if necessary to make the clock more accurate.

So precise that since 1967, a second has been defined as 9,192,631,770 oscillations of a cesium atom.

Explore the universe and the Earth

The laboratories of Katori and Ye have found ways to further improve atomic clocks by shifting oscillations towards the visible end of the electromagnetic spectrum, with frequencies a hundred thousand times higher than those used in current atomic clocks, to make them even more precise.

They realized they needed a way to trap atoms – in this case, the element strontium – and keep them still at ultra-low temperatures to help measure time correctly.

If the atoms fall due to gravity or otherwise move, there would be a loss of precision and relativity would cause distorting effects on the timing.

To trap the atoms, the inventors created an “optical network” made by laser waves moving in opposite directions to form a stationary shape in the shape of an egg box.

Ye is excited about the potential use of his clock. For example, synchronizing the clocks of the world’s best observatories to the smallest fraction of a second would allow astronomers to better conceptualize black holes.

Better clocks can also shed new light on Earth’s geological processes.

Relativity tells us that time slows down as it approaches a massive body, so a sufficiently accurate clock could tell the difference between solid rock and volcanic lava below the surface, helping to predict an eruption.

Or, measure the levels of the oceans, or how much water is flowing under a desert.

The next big challenge, according to Ye, will be to miniaturize the technology so that it can be moved outside of a lab.

The scientist admits that it is sometimes difficult to explain the fundamental concepts of physics to the public.

“But when they hear about clocks, they can feel it’s a tangible thing, they can relate to it, and it’s very rewarding,” he said.

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© 2021 AFP