Researchers are peering deep under the Canadian Shield, in the hopes of unlocking one of the secrets of the universe.

Physicists have long suspected that the universe is composed of more than meets the naked eye.

The biggest clue is the spin of galaxies. Based on observations, scientists say that, to spin the way they do, galaxies should be much bigger than they appear to be.

To explain the discrepancy, most scientists suggest every galaxy in the universe is surrounded by a swirl of nonbaryonic matter.

In theory, it's the influence of this heavy, but essentially invisible matter that exerts a gravitational influence on galaxies.

"There is a lot more mass than literally meets the eye," Associate Professor in Physics Juan Collar said in a statement. "When you look at the matter budget of the universe, we have a big void there that we can't explain."

Scientists have dubbed it dark matter.

You can't see it, or touch it, but scientists theorize that dark matter accounts for nearly 90 per cent of all matter in the universe. Compare that to the relatively paltry 4.6 per cent credited to visible or baryonic matter.

Determining the exact nature of this missing mass is one of the biggest problems confronting modern cosmology and particle physics.

Collar, with the University of Chicago, is a big player in the highly competitive race to confirm the presence of dark matter. The race has taken his team of researchers to a chamber deep under Sudbury, Ontario this summer.

Collar is the spokesperson for the Chicagoland Observatory for Underground Particle Physics (COUPP), a collaboration of scientists and students from the University of Chicago, Indiana University South Bend and the U.S. Department of Energy's Fermi National Accelerator Laboratory (Fermilab).

This month, Collar and his team are deploying the first of two dark matter detectors at SNOLab, the underground facility at the Sudbury Neutrino Observatory.

Built at a depth of 2 kilometres in Vale Inco's Creighton mine, SNOLab is the world's deepest permanent underground lab. That much rock overhead shields the same amount of natural radiation, including cosmic rays from deep space, as 6 kilometres of water.

Collar's team hopes to record evidence of a Weakly Interacting Massive Particle (WIMP), the leading candidate for cold dark matter.

Characteristics of WIMPs include:

• do not interact with each other, except through gravity
• have a large mass, compared to standard particles
• are relatively slow-moving

If they do exist, WIMPs should be constantly bombarding the planet. The only problem is, they rarely interact with ordinary matter.

In their efforts to record evidence of dark matter, some researchers use crystals, while others use liquefied gases.

Collar's team uses a tool familiar to mid-century particle physicists: the bubble chamber.

Essentially a jar of pressurized liquid, COUPP fills its chamber with the fire-extinguishing liquid iodotrifluoromethane, which boils at a single spot if struck by a high-energy particle.

By carefully adjusting the temperature and pressure of the liquid inside, the chamber can be tuned to ignore everything except WIMPs.

In theory, as WIMPs pass through the liquid they would leave tiny bubbles in their wake.

Waiting for bubbles

Once the bubbles are big enough, scientists can look for statistical variations that signal whether they were caused by background radiation or by dark matter.

So far, the standard model of particle physics doesn't account for dark matter. But Collar hopes to change that.

Collar is an old hand at the hunt, having deployed similar detection chambers in a series underground locations since establishing his research group in 2004.

So far, the COUPP collaboration has tested prototype detectors 330 feet underground in Chicago's Tunnel and Reservoir Project, 350 feet below Fermilab in Batavia, Illinois and in a sub-basement of the Laboratory for Astrophysics and Space Research on the UChicago campus.

"We started with a detector the size of a test tube and now have increased the mass by a factor of more than a thousand," Fermilab physicist Andrew Sonnenschein said in a statement.

The detector going into SNOLab this month weighs in at 4 kilograms. The second chamber due later this year is a whopping 60-kilograms.

While Collar and his peers hope their bubble chambers produce direct evidence of dark matter, other scientists are making and studying dark matter in particle accelerators.

But in the end, Collar expects it could be years before the physicists of the world can be convinced dark matter particles actually exist.

"It's going to take a lot of information from very many different points of view and entirely independent techniques," Collar said in a statement.

"One day we'll figure it out."