Heat is not supposed to behave like this. In everyday life, warmth seeps and diffuses, spreading from hot to cold in a slow, smearing process that never looks anything like a crisp sound wave. Yet ...

Sound is usually treated as the most familiar of physical phenomena, the background noise of daily life rather than a ...

"Second sound is the hallmark of superfluidity, but in ultracold gases so far you could only see it in this faint reflection of the density ripples that go along with it," study senior-author Martin ...