One of science's biggest puzzles is figuring out how interacting objects behave collectively. Take water, for example. "It's a molecule, but it's also a liquid with specific properties," says Daniel Sheehy, an assistant professor of physics at Louisiana State University. "How does the liquid come from the microscopic action of these water molecules?"
Sheehy doesn't study water, but he likes to use it to describe what he does study, which is many-particle quantum mechanics, that is, how atoms organize themselves at very low temperatures when they become trapped in beams of laser light, and whether they reach a superfluid state, a phenomenon that occurs only when it is extremely cold.
In a superconductor, the electrons form a superfluid which "is like a liquid, but better," Sheehy says. "It never slows down and the electrical resistance is zero, meaning none of the energy is lost."