At a lab here, 3,300 feet underground, Dr. Paling is searching for one of the most elusive objects in the universe: a wimp, or weakly interacting massive particle. Wimps are leading candidates for dark matter, which is believed to account for up to 95% of the mass of the universe. Something that big would be easy to spot except for the fact that dark matter is invisible. That doesn’t stop the elusive mass from making its presence felt by the immense gravitational tug it exerts on stars, galaxies and other cosmic bodies.

Mining for Dark Matter, Some Go Wimp-Hunting – WSJ.com