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Rare Element Could Make Timekeeping So Precise We Could Detect Dark Matter

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A neglected element languishing at the bottom of the periodic table could be used to build clocks so precise they could be used to find dark matter.

Physicists at the National University of Singapore have found that lutetium (Lu) holds promise for building extremely precise clocks. Currently, the world uses cesium atomic clocks to tell time. An atomic clock makes only one mistake in 300 million years, which means one that would have been built when dinosaurs were still around would still be on the dot up to this day.

But scientists do not really see lutetium as a replacement for everyday timekeeping. Scientists have a grander vision than that. They believe that ultra-precise clocks could open up possibilities for applications that are not possible with current technologies. These include detecting mini time warps caused by changes in the Earth's gravity field, thus allowing us to find dark matter and dark energy.

How A Cesium Atomic Clock Works

Ancient timekeepers have defined the second as 1/86,400 of a day. However, fluctuations in the Earth's rotation caused irregularities in how people all over the world tell time.

To create a global standard, the International Committee for Weights and Measures has decided to define a second by the frequency of microwave energy needed to move a cesium atom into an excited state. It takes exactly 9,192,631,770 pulses of microwaves to do that.

The Case For Lutetium Optical Clocks

In recent years, however, researchers have discovered that atoms such as aluminum and ytterbium can be used to build even more precise clocks. They use high-frequency visible light, adding more data points to the definition of a second.

However, these so-called optical clocks are highly sensitive to changes in temperature. This is why the less precise cesium clocks are still preferred. The discovery of lutetium as a timekeeper could be a game-changer as it is far less sensitive to changes in the temperature of its environment.

"We have definitively shown that Lu is the least sensitive to temperature of all established atomic clocks," says first author Kyle Arnold in a statement.

"The ultimate performance of a clock comes down to the properties of the atom — how insensitive the atom is to its environment," adds lead researcher Murray Barrett. "I would call lutetium top in its class."

What Is Dark Matter?

Dark matter is that part of the universe we can't observe. It has a gravitational pull but does not emit ordinary light. The theory is some 28 percent of the entire universe is made up of dark matter. Another 68 percent is said to be made up of dark energy, a mysterious force believed to cause the universe's rapid expansion.

The problem is there is currently no way of finding out if this theory is true. Lutetium optical clocks could possibly change that. According to Einstein's theory of relativity, gravity distorts time. And because there are differences in gravity in various parts of the world, time varies ever so slightly depending on where the clock is located.

Currently, atomic clocks cannot detect these time fluctuations. Lutetium clocks, which are a hundred times more precise, can help researchers map out the entire Earth's gravitational field by detecting the time differences around the world. And because dark matter exerts gravity, lutetium clocks could also be used to detect it and dark energy.

"Some theories that say dark matter is around us, so if we cross a chunk of dark matter, this would perturb the clock," Jérome Lodewyck, physicist at the Paris Observatory who was not part of the study, says.

The research is published in the journal Nature Communications.

Photo: Lane Pearman | Flickr

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