Evrim Yazgin
Cosmos science journalist
The quest to find dark matter is one of the ultimate pursuits of modern physics. Scientists have dug deep – literally – to try and find this elusive matter. But now some are thinking of a change in direction.
Dark matter is theorised to make up about 85 percent of the matter in the universe, with the other 15 percent accounted by visible matter.
Cosmologists are pretty sure it exists because of how they have observed stars in other galaxies orbiting the galactic centres. The orbits of stars far from the centre don’t make sense unless there is more matter in the galaxies than can be seen. A lot more.
Dark matter has dodged direct detection for decades, though.
Experiments searching for dark matter are already being built or underway. Such tests must be deep underground to reduce the “noise” from other particles, like muons, which zip through the apparatus. One such lab is the “Genius Lair”, housed in a gold mine under the Victorian town of Stawell.
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But, what if instead of looking down beneath our feet in the search for dark matter, we were to look up?
Physicists are now proposing a new way to look for dark matter by sending an atomic clock to the sun to act as a “quantum sensor”.
Dark matter distribution in the solar system is dictated by gravity. The sun makes up around 99.8-99.9 percent of our solar system’s total mass. Hence, in theory, we should be more likely to find dark matter around our central star, where the sun’s gravitational pull makes dark matter most dense.
Researchers from Japan’s Kavli Institute for the Physics and Mathematics of the Universe (IPMU), as well as University of California (UC), Irvine, and the University of Delaware – both in the US – have published a paper in Nature Astronomy outlining their proposed new dark matter detection method.
The team say they were partly inspired by NASA’s Deep Space Atomic Clock and the organisation’s Parker Solar Probe.
Parker has demonstrated that NASA’s new solar shielding enables spacecraft to get closer than ever to our sun. The Deep Space Atomic Clock represents the next generation of high-sensitivity atomic clocks which are used to navigate in space.
Read more: Underground ‘genius lab’ one step closer to finding dark matter
It’s not just any old dark matter that the team is hoping to find. Their method is specifically designed to seek out dark matter particles with extremely small masses.
Light dark matter is predicted to induce oscillations in certain universal constants, like the electron mass and the fine-structure constant which measures the strength of the electromagnetic force. Such fluctuations in these fundamental constants of nature would in turn affect the transition energies in atoms.
Atomic clocks work by measuring the frequency of photons emitted when atoms transition between different states. Any oscillations caused by dark matter would be detected as a different frequency photon being emitted.
“The more dark matter there is around the experiment, the larger these oscillations are, so the local density of dark matter matters a lot when analysing the signal,” says co-author Dr Joshua Eby from Kavli IPMU.
There is currently no plan to enact the concept. However, the researchers believe that future space missions using atomic clocks could double up as dark matter detection experiments.
“Long-distance space missions, including possible future missions to Mars, will require exceptional timekeeping as would be provided by atomic clocks in space,” says Eby. “A possible future mission, with shielding and trajectory very similar to the Parker Solar Probe, but carrying an atomic clock apparatus, could be sufficient to carry out the search.”