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My question concerns Sonoluminescence. I was amazed to learn that collapsing cavitations in liquids generate temperatures greater than 20,000 Kelvin. Is it possible that the vast amount of energy emitted by sonoluminescence is the result of the Casimir effect?

The bubbles are small and the walls are reflective. Could a standing wave exist for a short time within the confines of the oscillating cavity? Light emission could then be the result of fluctuations within the Zero Point Field, amplifying the standing wave to energy levels high enough to create virtual particles that are then annihilated, releasing the light and heat we see in sonoluminescence.

See for example:

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    $\begingroup$ Interesting hypothesis. That's been an even more fundamental question I've long been wanting to ask - is it even possible to sustain a standing wave resonance within a spherical cavity? If so, for the sonoluminescence one would think of a rapidly increasing frequency as the bubble goes through collapse, and an ever increasing localization of energy. $\endgroup$
    – docscience
    Nov 8, 2016 at 15:36
  • $\begingroup$ calculations of Casimir energies in spheres show that it becomes repulsive rather than attractive, so a collapsing bubble would actually make work against the cavity potential, which means that superficially it looks like a plausible explanation. The devil as always is in the details $\endgroup$
    – lurscher
    Mar 14, 2018 at 19:32

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Sonoluminescence is more likely due to the dynamical Casimir effect which is a case where vacuum oscillations are synchronized and made coherent with an oscillating conducting surface. The sound causes isotropic pressure variations inside the small bubbles causing them to change radius.

Why electric vacuum oscillations would become coherent for the specific frequency associated with the sound frequency in the surrounding medium is due to positive and negative feedback from the surface motion. It can be illustrated with synchronization of metronomes on a freely moving plate. The plate oscillation compares to the oscillating bubble radius. The effect is also similar to phase-locked loops and to astronomical orbital resonances. Multiples of vacuum frequencies can also similarly become coherent.

In most cases sound pressure and sound frequency is too small to change the pressure inside the bubble.

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