Videos demonstrating the sudden production of ice from supercooled water and the movie Frozen have come together to inspire a new way to search for dark matter while allowing us to better understand its nature.
YouTube hosts many videos demonstrating how you can put very pure water in an icebox and have it not freeze, only to very suddenly turn to ice with a single sharp bang. Some even explain the science behind it. Professor Matthew Szydagis of the University of Albany saw in these videos something no one else had; a way to explore one of physics' great unknowns.
"All of my work is motivated by the search for dark matter, a form of matter we're sure is out there because we can observe its indirect gravitational effects," Szydagis said in a statement. "It makes up a significant fraction of the universe, but we have yet to uncover direct, conclusive and unambiguous evidence of it within the lab." Physicists have been searching for such evidence for a long time, and progress has been surprisingly slow compared to many comparable areas of research.
Szydagis was reminded by the videos that water can be cooled far below its freezing point of 0ºC (32ºF) and stay liquid if it does not have something to nucleate around. The nucleation site that causes freezing can be almost any impurity, but as the videos show it can also be a physical disturbance. Watching Elsa provide the nucleation in Frozen made Szydagis think of the effect again, and wonder if subatomic particles, like the ones that hypothetically make up dark matter, could act as nucleation sites.
After cooling purified tap water to -20ºC (-4ºF), Szydagis tested whether radiation can cause freezing. Some types can, but the product is more like snowflakes than solid ice. Szydagis dubbed his test equipment a “snowball chamber”, making a trifecta with existing “bubble” and “cloud” chambers also used for subatomic particle detection.
Super-cooled water turning into snow in slow-motion. Joshua E. Martin
"To our great surprise, we found that some particles (neutrons) but not others (gamma rays) trigger freezing,” Szydagis said, presenting his work at the American Physical Society Meeting.
The findings confirm that cosmic rays can trigger cloud formation in the upper atmosphere, even in the absence of aerosols like dust. The chambers could be useful for identifying specific types of radiation, such as those from smuggled uranium, but Szydagis will not let the dark matter go.
Dark matter was discovered when Vera Rubin established galaxies' rotation rates require far more gravitational force than their stars alone provide. However, the particles that are thought to make up much of dark matter don’t behave like more familiar material in other ways, which is why they are so hard to detect. On arXiv, Szydagis argues these snowball chambers provide “inexpensive, scalable detectors for low mass [particles]” outside the energy range where the dark matter search has concentrated.