Dark matter is an enigmatic beast. We can't see it, yet we know it makes up most of our universe. Finding the mysterious particle (or particles) the exotic matter is composed of has puzzled and intrigued scientists for decades.
On June 6 at the Planck 2019 conference, an international meeting highlighting frontier physics research, John Terning and Christopher Verhaaren, theoretical physicists at the University of California, Davis, presented a new theory for what makes up dark matter and how we might detect it. A preprint paper of their study was uploaded to the arXiv directory on May 31.
Dark matter and dark energy, two theoretical forms of matter, are thought to make up more than 85% of the known universe. When we look out into, the evidence for the existence of dark matter is plentiful -- we can see the effect it has on gravity and the expansion of the universe. We know something, an invisible particle perhaps, is lurking out of sight and responsible for the way our universe works.
Scientists have long struggled to find the elusive, exotic particle that makes up dark matter, and more theories abound every year. In December, an Oxford scientist proposed that theOthers have suggested hunting for dark matter in cutting-edge new ways. Still, we have failed to detect it.
Which brings us to Terning and Verhaaren's idea. They argue for a new "type" of dark matter and a way to detect it, a one-two punch of theory and experimental validation. However, the authors of the study caution that verifying it could take quite some time.
The new type of dark matter is different from previous theories, which suggest the exotic, invisible particles may be made up of weakling interacting massive particles, or WIMPs. No experiments have been able to find these particles, though scientists have built large, shielded laboratories that hope to reveal them.
"We still don't know what dark matter is," said Terning in a press release. "The primary candidate for a long time was the WIMP, but it looks like that's almost completely ruled out."
The researchers looked at an opposing theory for dark matter with an equally fantastical name: "dark electromagnetism." It says there's a subatomic particle known as a dark photon which sometimes interacts with regular photons that we can already detect. The duo added their own spin to the idea by showing dark matter might be caused by "dark monopoles," which are based on quantum theory.
It all gets very tangled here, especially for us mere mortals struggling with everyday physics. The bottom line? We've got a new theory which proposes the "dark monopole" could be detected in an experiment thanks to its interactions with regular photons and the Aharonov-Bohm effect, which has been proven experimentally.
However, the observable effect would be incredibly small -- even smaller than gravitational waves -- and we don't yet have the technology to detect such minute signals right now. Alan Duffy, a dark matter researcher at Swinburne University in Australia, notes how the first detection of gravitational waves (itself only a theory until recently) took "a century of heroic scientific and engineering effort" suggesting that might be "a worry for the testability of the [new] prediction."
Where does that leave Terning and Verhaaren's theory? Well, as a theory, of course. But that's where all good science starts.