There’s something wrong with the Universe

Galaxy: Galaxies spin at tremendous speed. Scientists speculate an unseen gravity source—<em>dark matter</em>—keeps them from flying apart
Galaxy: Galaxies spin at tremendous speed. Scientists speculate an unseen gravity source—dark matter—keeps them from flying apart
Courtesy Courtesy NASA/JPL-Caltech

The stars shimmering in the night sky are constantly moving. As they pass one another, the pull of their gravity makes them circle, like skaters grabbing hands as they pass.

The strength of this gravity depends on the mass of the stars. But when scientists add up all the stars in a galaxy, they find there’s not enough mass to keep them together. At the speed the stars move, they should have flown apart eons ago. Something else must be helping keep them together.

Scientists speculate that something else is dark matter—exotic material that has mass (and thus gravity), but which otherwise scarcely interacts with atoms. This makes it almost impossible to detect.

We call this theoretical material WIMPs—Weakly Interacting Massive Particles. If each galaxy was filled with a cloud of invisible WIMPs, it would explain the movements of the heavens.

But only if they actually exist.

Digging deep to solve nature’s mysteries

In the inky blackness at the bottom of an abandoned mine, Cushman and her team have built one of the most sensitive devices ever conceived.

They hope to detect the movement created when a WIMP collides with an atom. But WIMPs are so small in theory that most of them pass between atoms—only one in ten billion would score a direct hit.

Entrance to Soudan mine
Entrance to Soudan mine
Courtesy Fermilab

To sense these rare events, the scientists must eliminate all other factors that might make an atom move. They cool the instrument to the point where the atoms themselves sit almost perfectly still. A half mile of rock blocks cosmic rays that might spoil the experiment, and 200-year-old lead from a French shipwreck shields the device from radioactivity.

With the detector at the ready, scientists watch to see if any WIMPs are bold enough to make their presence known.

Click here for an animation of the experiment, and an effort to turn scientific data into music!