The secret to direct detection of dark matter may be gone with the wind.
Even though this mysterious substance has a weight ratio of about 8 to 1 visible matter in the universe, scientists continue to elude it. All laboratory attempts to directly detect dark matter — visible only indirectly through its gravitational effects on the motions of stars and galaxies — have gone unfinished.
These attempts rely on dark matter having at least some other interactions Ordinary matter other than gravity (Serial Number: 10/25/16). But a proposed experiment called Windchime, while still decades away, will try something new: It will use the only force it can guarantee to feel—gravity—to search for dark matter.
“The core idea is very simple,” said theoretical physicist Daniel Carney, who described the plan at the American Physical Society’s Division of Atomic, Molecular and Optical Physics meeting in Orlando, Florida, in May.As easy as the rattling of the windchime on the porch, the Windchime detector will Attempts to sense dark matter ‘winds’“As the solar system revolves around the Milky Way, it blows past Earth.
If the Milky Way is primarily a blob of dark matter, as astronomical measurements suggest, then we should be sailing through it at around 200 kilometers per second. This creates dark matter winds, like the wind you feel when you stick your hand out the window of a moving car.
The Windchime detector is based on the concept that a set of pendulums swing in the breeze. In the case of a backyard wind chime, it could be a metal rod or a hanging bell jingling in the flowing air. For dark matter detectors, the pendulum is an array of tiny, ultrasensitive detectors that are jostled by the gravitational force felt by the dark matter fragments they pass through. Instead of air molecules bouncing off a metal bell, the gravitational pull of the particles that make up the dark matter wind creates unique ripples as it blows past the billion or so sensors in a box about a meter on each side.
While it seems logical to use gravity to search for dark matter, in the nearly 40 years that scientists have been searching for dark matter in the lab, no one has tried it. That’s because, relatively speaking, gravity is a very weak force that is difficult to separate in experiments.
“You’re looking for dark matter [cause] Gravitational signals in sensors,” said Carney of the Lawrence Berkeley National Laboratory in California. “And you just ask. . . can I see this gravitational signal? When you first make an estimate, the answer is no. This will actually be very difficult. “
That didn’t stop Carney and a small group of colleagues Explore this idea anyway in 2020. “30 years ago, this suggestion was completely crazy,” he said. “It’s still a bit crazy, but it’s borderline crazy.”
The Windchime project collaboration has grown to include 20 physicists. They have a prototype Windchime built from a commercial accelerometer and are using it to develop the software and analysis to produce the final version of the detector, but it’s far from the final design. Carney estimates that it may be several more decades before sensors sufficient to measure gravity, even from heavy dark matter, are developed.
Carney bases the schedule on Laser Interferometer Gravitational Wave Interferometeror LIGO, which seeks to find gravitational ripples from black hole collisions (SN: 2/11/16). When LIGO was first conceived, it was clear the technology needed a 100 million-fold improvement, he said. Decades of development have created an observatory that can observe the sky through gravitational waves. For Windchime, “We’re in the same boat,” he said.
Even in its final form, the wind chime is only sensitive to fragments of dark matter roughly the mass of a tiny grain of dust. That’s huge on the spectrum of known particles — more than a trillion trillion times the mass of a proton.
“There are a lot of very interesting dark matter candidates [that scale] It’s definitely worth looking for … including primordial black holes from the early universe,” said physicist Kathryn Fries of the University of Michigan, Ann Arbor, who was not part of the Windchime collaboration. She noted that black holes slowly evaporate, leaking mass back into space, which could Will leave many vestiges on the mass detectable by Windchime shortly after the Big Bang.
But if it doesn’t detect anything at all, the experiment would still stand out from other dark matter detection schemes, said Dan Hooper, a physicist at Fermilab in Batavia, Illinois, who is also not affiliated with the project. That’s because this will be the first experiment that can completely rule out certain types of dark matter.
Even if the experiment turned out nothing, Hooper said, “It’s amazing that [Windchime] …isn’t, independent of anything else you know about dark matter particles, they’re not in this mass range. ” and Existing experimentsthe failure to detect anything could be due to wrong guesses about the forces affecting dark matter (SN: 7/7/22).
Windchime will be the only experiment so far that hasn’t seen anything that would definitively tell researchers what dark matter isn’t. With any luck, though, it might spot a tiny wind of black holes, or even more exotic fragments of dark matter, blowing by as we fly around the Milky Way.