From 1876 to 2001, the Homestake mine in South Dakota yielded almost 1400 tons of gold. It shut down when costs went up and gold prices went down. Today, though, the mine is just about as busy as ever. Hundreds of scientists use its tunnels as laboratories. Shielded from radiation from space, it’s a good site for trying to catch exotic particles — especially dark matter. In fact, the world’s most sensitive dark-matter detector finished its first test run this year. It didn’t find any dark matter, but it did show that it’s ready to look for it. Dark matter exerts a gravitational pull on the normal matter around it. And it appears to account for about 85 percent of all the matter in the universe. But it produces no energy, so we don’t know what it is. The leading idea has been that it’s a type of heavy particle. But no experiment has seen any such particles. The new experiment is LUX-ZEPLIN — L-Z for short. It’s almost a mile below the surface. It consists of a tank filled with seven ton
