eli5: I saw a post on instagram saying “Sonoluminescence – If you collapse an underwater bubble with a soundwave, light is produced, and nobody knows why” is this true?
In: Other
So here’s the reality at hand.
When things get hot, they give off light. When they get hot enough, that light is in the spectrum where we can see it.
If we use sound waves ever so carefully, we can open a tiny little vacuum in water. And when we stop applying those waves, the “bubble” will collapse from the pressure. Water filling the cavitation from all directions at the speed of sound in water, colliding with the point opposite in the bubble at twice the speed of sound.
That produces heat. Why do we know it produces heat? Because the kinetic energy has to go *somewhere*. Some becomes sound which will eventually become heat, and the rest will just be heat. And what’s heat? It’s light. Photons.
It’s not some mystery. Have we directly observed the temperature spike? Yes. Have we confirmed that it’s enough to release visible-spectrum photons? Well, no, but water is an incredibly efficient thermal insulator so it’s nearly impossible to measure the heat. And there’s no financial benefit to building an apparatus to confirm something that takes in much more energy than it puts out just because it looks cool.
Point is, we know what’s happening. It just hasn’t been confirmed empirically.
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