Instead, researchers rely on their ability to track the ethereal substance’s effect on its surroundings—an unexpected shift in gravity’s pull or seemingly inexplicable bending of the very light waves we rely on for sight.
“Light is impacted by gravity, it feels its influence,” said Rainer Dick, a professor in the University of Saskatchewan’s Department of Physics and Engineering Physics. “When light comes close to a very large mass, it’s also bent in its path. There’s actually a way to put galaxies and galaxy clusters on scales and to weigh them, by measuring the bending of the light around them. The larger than expected bending of light among galaxies and galaxy clusters is evidence of dark matter.”
Dick is one of many researchers around the world who are on the hunt for dark matter, exploring new and exciting ways to try to pin it down and prove once and for all that it actually exists. The material, which experts estimate makes up roughly 80 per cent of the mass in galaxies, plays a vital role in keeping galaxies from ripping apart as they spin through the cosmos.
“It’s the stuff that binds together galaxies through the effect of gravity,” said Dick. “Without this dark matter, the outermost stars would actually leave the galaxy because they have such high velocities.”
The substance draws its name from its unusual relationship with light, which renders it invisible to all but the most precise of instrumental measurements.
“It does not reflect light. It does not emit light, it does not absorb light and it does not reflect light, so we cannot see it with our eyes,” Dick said. “It’s perfectly dark, from that perspective.”
Dark matter straddles an unusual line in physics, Dick said, in that it technically has not been proven to actually exist, despite over- whelming evidence to the contrary.
“The outskirts of galaxies would not look the way they do without the existence of dark matter,” he said. “The universe is close to 14 billion years old and it’s filled with large-scale structures like galaxies, huge structures of many galaxies and filaments of galaxies connecting each other. Ordinary matter would not have the time, even in 14 billion years, to generate these large-scale structures. It needs a large amount of dark matter.”
Any potential application for dark matter would be purely theoretical at this point, as it interacts with everyday matter only in extremely weak, barely noticeable ways. But Dick is hesitant to write off technical uses entirely, citing electromagnetic waves as just one famous example of research similarly presumed useless prior to its confirmation by researcher Heinrich Hertz.
“Hertz had to write a funding application for that to the Prussian Academy of Science, and they wrote back that it would never be good for anything, but would be so important for science that it should be funded anyways,” Dick said. “Twenty or thirty years later, people use that on a technical scale every day for radio and signal transmission across the Atlantic.”
Dick has produced three peer-reviewed papers on quantum theory in the past 12 months and will lead a discussion on new dark matter research at an international conference later this month. For researchers around the world like Dick, who is currently in the process of publishing new results on dark matter research, the search for answers continues.
“There’s actually dark matter in this room,” Dick said. “Every now and then—very rarely—they interact with ordinary matter extremely weakly. They bounce off an atomic nucleus and generate a tiny little recoil in it. That’s what people are looking for.”