A New Generation of Atomic Clocks Could Help Find Dark Matter

Detecting Dark Matter

For years, researchers have been hunting for dark matter, which is thought to make up about 27 percent of the entire known universe. Now, an innovative team of scientists says they may have figured out a new way to detect the elusive substance using an international network of atomic clocks.

In 1998, with observations from the Hubble Space Telescope, scientists found that the universe was expanding faster and faster, which contradicted the expectation that gravity would slow it down. Based on that discovery, scientists believe there must be a mysterious material (now known as dark matter) that is pushing the universe to expand faster. But dark matter has yet to be detected or even understood.

With a new generation of super-precise atomic clocks, an international team of researchers says they may have a new way to catch dark matter as it interacts with regular matter — something that scientists assume must happen, but haven’t yet been able to see.

Atomic Clocks

All clocks rely on stable oscillators, like the pendulum in a grandfather clock or the earth’s rotation for a sundial. In an optical lattice atomic clock, a type of atomic clock that’s still being developed and perfected, atoms act as the oscillator.

In these clocks, a laser is shined through a cloud of atoms — usually of strontium or ytterbium. This laser excites the atoms to oscillate, or move back and forth hundreds of trillions of times per second. The oscillating atoms act like the hand on a watch, if a watch had a hand that ticked insanely fast. Atomic clocks of this design are supremely accurate — the current generation won’t lose a second for billions of years to come.

That accuracy makes them ideal for making very small, very precise measurements, including, perhaps, of dark matter. Without any interference from dark matter, the atoms in an optical lattice atomic clock will oscillate at an expected frequency. The presence of dark matter would affect this frequency through the interactions between dark matter particles and regular matter. Any observed frequency dips or spikes would then be evidence for dark matter.

Creating a Network

In this study, researchers used four optical lattice atomic clocks, placed in Colorado, France, Poland, and Japan. This is the first time that a network of these atomic clocks has been created. By having more than one atomic clock in a network, scientists can make more observations and help tune out some of the noise that comes from having only a single data source, said physicist Piotr Wcisło, who led the study, in an email.

Additionally, having the atomic clocks in different countries is advantageous. As Wcisło explained, “the clocks are separated therefore we do expect to see any correlations in signal other than some global physical effects.”

The first version of the network allowed the researchers to place further constraints on the size of the expected effects any dark matter interaction might have. That is, they didn’t find anything yet, but they’re narrowing the search down.

This work is detailed in the journal Science Advances.