Sonoluminescence¿the physical phenomenon by which sound turns into light¿is as mystifying as a magic trick. Despite 70 years of trying, scientists still cannot fully explain how a bubble of air in water focuses acoustic energy a trillionfold to spit out picosecond bursts of ultraviolet radiation. Initially physicists attributed the flashes to friction. In the late 1980s, though, they came to see that bubbles in a sound wave's path expanded and rapidly collapsed¿heating the gas inside them to temperatures hotter than the sun's surface. This collapse and heat, they determined, created a glowing plasma. In this week's issue of Physical Review Letters, Gary A.
