The human eye is adept at picking out the smallest glimmer of light in shadowed spaces and the faintest star in the heavens (but light pollution has made this very hard). Mysterious flashes of light have always piqued our interest — and this is perhaps where sonoluminescence was born.
When two German engineers were studying sonar — the use of sound to navigate, like bats — in 1934, they stumbled upon a strange phenomenon: when a small bubble trapped in a liquid is hit by powerful sound waves, it seems to produce a flash of light.
The cause turned out to be straightforward, if also fascinating: the alternating high- and low-pressure phases of sound waves caused the bubble to expand and collapse rapidly. During the collapse, the bubble compressed so intensely that the temperature inside soared to several thousand kelvin. The extreme temperature caused gases within the bubble to ionise and release light energy in about a trillionth of a second.
We don’t know how exactly this light is produced — yet. The world has more mysteries than we like to admit.
Sonoluminescence isn’t restricted to labs. Pistol shrimp (family Alpheidae) possess a specialised claw that it can snap shut with incredible speed. The result is a jet of water moving so fast that it creates a low-pressure bubble in the water. And when this bubble collapses, it generates a loud sound, intense heat, and, if you’re lucky (or unlucky?) to be nearby, a fleeting flash of light…
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