Physicists capture first sounds of heat 'sloshing' in a superfluid, revealing how heat can move like a wave

In most materials, heat prefers to scatter. If left alone, a hotspot will gradually fade as it warms its surroundings. But in rare states of matter, heat can behave as a wave, moving back and forth somewhat like a sound wave that bounces from one end of a room to the other. In fact, this wave-like heat is what physicists call "second sound."