Physicists capture 'second sound' for the first time — after nearly 100 years of searching - Live Science

First theorized in 1938, heat's wave-like flow through superfluids, known as "second sound", has proven difficult to directly observe. Now, a new technique has finally done it, and could be used to stScientists have captured direct images of heat behaving like sound — an elusive phenomenon called 'second sound' — for the very first time. Imaged within an exotic superfluid state of cold lithium-6…