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.” Signs of second sound have been observed in only a handful of materials. Now MIT physicists have captured direct images of second sound for the first time….
