These atomic clocks are so accurate that they measure the distortion of space-time – Science News

These clocks are so accurate that they would only lose a half-second if they lasted at the age of the universe. It is 14 billion years old.

But they will not be used to keep the trains on time. The exquisite precision of the clocks, described in Nature today, means that they can measure the distortion of space-time caused by the forces of gravity.

Finally, astrophysicists could ask for their help to detect a mysterious dark matter.

More immediately, the clocks could tell us what's going on inside the Earth by accurately mapping the bumps and bumps of our planet – if the clocks are narrowed, that's it.

The co-author of the study, Will McGrew, a PhD student at the US National Institute of Standards and Technology, said that "ticking" clocks is produced by the oscillations of radiation emitted when electrons in ytterbium atoms are excited by lasers.

It turns out that they tick, almost in unison, 500 trillion times a second.

"Measuring time and frequency with such incredible accuracy provides a really powerful lens for visualizing the natural world," McGrew said.

Atomic Time 101

The measurement time was based on astronomy. For example, the duration of a day was determined by a turn of the Earth on its axis.

But astronomical phenomena tend to slow down or accelerate.

Our days are getting longer by 1.7 milliseconds a century, thanks to our attractive tango with the moon.

So, while astronomical time can do things like that, science requires precision.

And that's where the atomic time shines.

Rather than looking skyward, this form of time measurement penetrates waves of radiation rejected by atoms as they bathe in laser light.

They look super futuristic, but atomic clocks have been around for more than 60 years.

The first atomic clock accurate enough to be used to set the time was built in 1955 at the National Physical Laboratory of the United Kingdom.

It was accurate to one second in 300 years.

Some 12 years later, the cesium atomic clock has become the international standard and, over time, atomic clocks have become much more precise.

Modern atomic clocks that use strontium or ytterbium instead of cesium lose a second every 300 million years.

More than timekeepers

The accuracy of atomic clocks means that they have tested Albert Einstein's theory of general relativity, which predicts that time turns faster or slower under the influence of different gravitational forces.

In other words, a clock placed on a satellite orbiting the Earth, whose "gravitational potential" is higher, will be faster than the clock at sea level.

And there are already atomic clocks whizzing around the Earth on satellites that take advantage of this temporal dilation effect.

We would not have the global positioning system, or GPS, without them.

Another use of satellite-mounted atomic clocks is to accurately map the size, shape, orientation in space and mbad distribution of the Earth, collectively called "geodesy".

Satellite geodesy typically involves determining the time it takes for light to move between distant points, for example, turning a laser on a satellite and the time it takes for it to bounce off a receiver. earthly.

GPS geodesy is accurate to the nearest centimeter, said Matt King, who uses satellite geodesy at the University of Tasmania and did not participate in the study.

But clocks with a higher "tick" rate – that is, a higher frequency – would not have to use light at all. They could use the relativistic effects of gravity.

That's what Mr. McGrew and his colleagues wanted to achieve with their atomic clock.

Instead of cesium, they used ytterbium. The radiation waves emitted by the ytterbium atoms oscillate nearly five orders of magnitude more rapidly than those of cesium atoms.

In their document, the team showed that the clocks were exceptionally stable – that they lost or gained time almost imperceptibly – worked almost in unison.

Thus, by comparing the difference in ticking between two ytterbium clocks placed on separate continents, a person could measure the difference in height between clocks to less than one centimeter.

Exploiting the precision of ultra-sensitive atomic clocks would be like "having a telescope looking in," said Professor King.

"Say you have an earthquake," he said.

"If you can really measure that accurately, you will be able to learn about the fundamentals of the Earth's interior, such as its viscosity or rigidity."

The way the Earth bounces when glaciers melt or sink when groundwater is pumped can also be followed with atomic clocks.

And seeing how the soil around a volcano rises and sinks, even on a scale less than a centimeter, could tell volcanologists how the magma moves beneath it, added Professor King.

"Combine that with seismology, and you get a real picture of what's going on inside."

Large applications, compact clock

So, what prevents atomic clocks from being broadcast in volcanic and earthquake risk locations around the world?

Simply, ytterbium clocks are great to move.

"[The clocks] basically a pretty big lab, "said McGrew.

That's because they need a bunch of big lasers to work.

A couple of lasers cool the ytterbium atoms to a fraction of the absolute zero (-273 degrees Celsius), while others keep the cooled atoms in place.

Mr. McGrew and his colleagues have already started working on systems reduction.

Professor King is optimistic that ultra-precise atomic clocks will one day be compact enough for use on Earth as well as in space.

"Computers also filled whole rooms.

"We may be in 20 years, maybe it will be sooner, but if these [ytterbium clocks] can be miniaturized and if the accuracy continues to increase, applications are not lacking. "

Weird and wonderful

Downstream of the track, atomic clocks could be used for experiments involving the measurement of smaller spatio-temporal distortions, such as the extremely subtle stretching and crushing of matter caused by a gravitational wave.

Take dark matter, for example. Astrophysicists know that dark matter is present and that it forms about a quarter of the entire mbad and energy of the universe.

But its "dark" nature – that it does not seem to reflect, absorb or emit radiation – means that it is very difficult to detect.

A dark matter model suggests that it might interact with ordinary matter by changing the fundamental constants of nature, McGrew said.

And this is where atomic clocks could help astrophysicists learn a little more about these elusive objects.

"Suppose that a large dark matter object pbades through a lab equipped with a ytterbium clock and a strontium clock," said Mr. McGrew.

"[The dark matter] would affect ytterbium by one factor, then strontium by another factor.

"By measuring the difference between the two clocks, you can detect the presence of the dark matter object.

"These are extremely subtle effects, but when you can do measurements with 18-digit precision, you can detect them."

And, of course, there are goals we have not dreamed of yet.

"The people who made the first atomic clocks did not know that they were building a GPS device," McGrew said.

"I think there is something similar to say about atomic clocks – that their most salient, most important applications have not yet been thought of."