Two tiny dots encircled and projected on a screen in the University of Minnesota's physics building Friday afternoon signaled a potentially monumental discovery.
As a roomful of sometimes skeptical scientists looked on, a researcher stated his case for why a group of physicists believe that in a northern Minnesota lab at the bottom of an old iron mine a half-mile underground, they may have discovered a key to understanding the universe:
It is believed to account for most of the universe's total matter. If its existence can be proven, it would go a long way toward unlocking celestial mysteries that have baffled scientists.
"There is not enough gravity in observable matter to keep stars and galaxies together," said Marvin Marshak, the University of Minnesota physics professor who directs the lab at the Soudan underground mine near Ely. The fact that these spiraling entities don't fly apart suggests that something else holds them together, something humans can't see.
How they've searched for it reads like science fiction: Deep underground, away from the worst interference from cosmic rays, they installed 30 cryogenic detectors out of germanium and silicon and cooled them to nearly absolute zero -- minus 459.69 degrees Fahrenheit.
Then, those part of the Cryogenic Dark Matter Search experiment monitored the detectors for signs of collisions caused by weakly interacting massive particles [WIMPs], which could be a type of dark matter created just before the Big Bang.
Particle physics theories suggest that WIMPs would rarely interact with normal matter but may occasionally bounce off or scatter from an atomic nucleus like billiard balls, leaving a small amount of energy that is detectable under the right conditions. The Soudan lab has been searching for WIMPs since 2003.
"What they're looking for is the simultaneous release of electrical energy and heat," Marshak said. "Heat is hard to detect. So you chill the detector so that very little heat makes a measurable temperature rise."
Recently, they detected what they believed could be two such collisions, described by officials at the federal government's Fermilab, which is part of the experiment, as "two events that have characteristics consistent with the particles that physicists believe make up dark matter."
Oleg Kamaev, a postdoctoral researcher at the lab, projected an image of how those collisions looked -- the two tiny dots -- at Friday's event at the U. The results await corroboration by the collection of more data more sensitively measured by bigger detectors, as well as other independent studies.
"Within a year of two, we should have a pretty good idea if this is right," said Marshak.
If the collisions, each monitored in a separate detector, hold up to scrutiny, it will be Earth-shaking, but that remains a big if. Chances of the dark matter readings being false positives are roughly one in four, Kamaev explained.
But one reason for optimism is that the results came deep underground. The Soudan lab hosts some of the world's most sensitive equipment, Marshak said.
"Half-a-mile of Earth is the filter" for many of the cosmic rays and other fallout that could contaminate findings, he added. "The problem is you can never get rid of everything else. If they were unlucky and got a lot of outside stuff, then this is a lot of nothing."
Marshak and Fermilab officials remain cautiously optimistic. A breakthrough could eventually add exponentially to understanding the universe, scientists say.
"This kind of basic research underlies the technology that affects our lives," explained Marshak, who gave an example of how science gets applied. "I'm sitting in Los Angeles right now talking to you by talking into my laptop."
The applications of dark matter to technology are years, if not decades off.
Marshak said searchers plan to install larger detectors in an even deeper lab in Canada. The larger equipment hopefully will measure more of the disturbances of the type witnessed at Soudan, statistically ruling out chances of a false positive, Marshak explained. Also, other scientists will try to duplicate the results from Soudan. Finally, Marshak said, theoretical physicists "will decide if this thing that has been measured is enough to hold the galaxy together."
As Kamaev told his colleagues at the University of Minnesota Friday afternoon, "Stay tuned."
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