Superfluids are supposed to flow indefinitely. Physicists just watched one stop moving

Ordinary matter, when cooled, transitions from a gas into a liquid. Cool it further still, and it freezes into a solid. Quantum matter, however, can behave very differently. In the early 20th century, researchers discovered that when helium is cooled, it transitions from a seemingly ordinary gas into a so-called superfluid. Superfluids flow without losing any energy, among other quantum quirks, like an ability to climb out of containers.