We're rarely reminded that everyday matter is made of atoms bound tightly to one another by their charged electrons. Slicing bread doesn't feel like splitting atoms, or driving a wedge between the electric forces of molecules. Slicing bread isn't, in fact, splitting atoms; though the drag on the knife as it moves is the ghostly grip of displaced electrons as they redistribute themselves among molecules parting from one another under the blade.
But crack ice or bite a wintergreen Lifesaver, and they will flash with light visible in a darkened room. These are fluorescent lights in miniature, activated by electrons stranded on the wrong side of a broken atomic bond where crystals of water or sugar fracture, then suddenly crossing the microscopic gap to ionize intruding molecules of air, in numbers and force enough to be seen by the unaided eye. It is the subatomic realm reaching up violently to the macroscopic world with no more urging than the mechanical energy that one hand can muster.
These are exotic phenomena, but they are not yet answers to the dream of great forces from the gentlest summons. The energy released in these forms of unexpected luminescence is limited by that available in the chemical bonds along the plane of fracture alone. It is energy of the slice and not the whole.
Sonoluminescence releases, literally, power of another dimension. When ultrasound passes through a liquid medium – water will do just fine – it can sparkle with light from the transient bubbles induced. Like the light from ice, it is of a lower order. But as a laser is only fluorescent light that has been purified and made orderly, the energy liberated by nothing but bubbles can be extravagantly increased by simplifying its driving forces. Make the sound a single accurate frequency, say 20,000 Hertz; and restrict the effect to a single bubble, perfectly formed thereby. The first time both of these were done at once was at the University of Mississippi. The ultrasound creates and sustains a bubble that expands and contracts symmetrically with the same frequency as the standing wave it's embedded in. In one twenty-thousandth of a second the bubble collapses in size by a factor of 50, and the implosive force is correspondingly extreme. Within the bubble trapped gas turns to plasma that easily exceeds the temperature of the sun's surface. It's not even necessary to dim the laboratory lights to see the glow from a single bubble a twentieth of a millimeter in diameter.
The measure of that energy release has just recently been taken by UIUC researchers. And at the bubble's quickly contracting core, where photons cannot escape to be detected, things may be hotter yet. Sufficiently provoked, it may even cross the threshold of fusion. If so, the bubble would not just be a bright light, but a miniature sun.
Exactly how this happens is still unknown. Mysteriously, adding noble gases to the water multiples the intensity of the effect. A dash of sulfuric acid increases it further still. What other increases may be possible is anyone's guess. It's a new science, with far to go. Even if it falls short of fusion, it's still the most powerful mechanically-induced energy known — extraordinary force from ordinary means.
Latest measurements, background on sonoluminescence, and wintergreen Lifesavers explained