Here’s what you’ll learn when you read this story:
Dark matter is thought to make up a little over a quarter of the universe, but it has never actually been detected.
Researchers repurposed an experiment originally intended to detect gravity, which involved a floating magnet in a superconductive trap, predicting that gravity exerted by dark matter would interact with the magnet.
The experiment is now being upgraded from a gravity detector to a dark matter detector, so expect version 2.0 soon.
What we think of as ‘the unknown’ isn’t always some hypothetical wormhole or alternate dimension. A lot of times, the ‘unknown’ is something real, but whose existence is impossible to prove even with the most advanced technology. We’re talking about dark matter, which remains infamously elusive.
From huge, hypersensitive underground detectors to the search for bizarre signatures in comic rays, it seems we have tried everything within our current capacity to directly observe even one particle of dark matter. But we do know a few things about this mystery matter—namely, that it exerts gravity, and therefore (supposedly) has mass. When gravitational forces exerted by bodies in space are beyond what is expected, dark matter is the explanation (but never the evidence).
Maybe, however, dark matter could make its presence known another way. Astroparticle physicist Christopher Tunnell, of Rice University in Houston, saw an alternative method of detecting ultralight dark matter by repurposing what was originally a precise method of measuring gravity. This method uses a magnet floating in a chamber made of superconductive material. When cooled enough to transition to a state in which they can conduct electricity without resistance, superconductors expel magnetic fields and therefore repel magnets. This explains why a magnet in the middle of a superconductive trap will float right in the middle. It is being repelled in every direction, and there is nowhere else it can possibly go.
Tunnell and his research team predicted that dark matter could be detected this way because of its quantum nature, meaning that it is thought to behave as both a particle and a wave. Dark matter can only interact with baryonic (normal) matter through gravity. If any dark matter came close to the levitating magnet—whether it behaved like a particle meandering around or a wave flowing through—the force of gravity it exerted should give the magnet an almost negligible shake. A quantum device known as a SQUID (Superconducting Quantum Interference Device) was used to detect any shifting of magnetic fields that would happen if gravity from an unseen source interacted with the magnet.
“We detect the motion of the particle using a superconducting pick-up loop at the top of the trap,” Tunnell said in a study recently published in Physical Review Letters. “The motion of the magnet induces a change in flux in the loop, causing a superconducting current to run in the circuit.”
Spoiler alert: dark matter has not been detected with this method so far. But it has potential. Tunnell plans to update the experiment and optimize it specifically for detecting dark matter instead of gravity. Some of the changes that could make it more sensitive include maximizing sensitivity to mass while reducing noise, using a heavier magnet, reducing vibrations in the trap, and upgrading the SQUID so it can more accurately detect changes in the magnetic field. This new proposed experiment will be named POLONAISE, after a Polish dance Tunnell and a colleague were doing to keep warm at an outdoor climate protest.
“Our result highlights the promise of this quantum sensing technology in the hunt for dark matter,” he said. “We hope that it fuels initiatives in advancing experimental designs of magnetically levitated setups for astroparticle physics.”
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