Energy-concentrating phenomena

Posted April 19, 2006

Ordinarily I don't attend too many physics talks off-campus, despite a rich constellation of them in the vicinity of Cambridge. Every once in a while I run across one that is just too good to miss despite a long walk, though, and yesterday was such an occasion: Seth Putterman from UCLA came to Boston University to give a lecture on energy-concentrating phenomena, such as his work on sonoluminescence and pyrofusion.

I'd been peripherally aware of these developments for a while, but I just didn't have a good appreciation for how weirdly fascinating they actually are. The general theme was how various low-energy, slow fluid and solid processes sometimes result in high-energy, fast phenomena. For a physicist like me, this immediately piques my interest, because you usually don't expect natural processes to "focus" like that: it's the sort of thing that technology does, whereas nature more prefers to smooth things out and slow outliers down.

Examples. The sonoluminescence process takes room-temperature water subjected to normal (albeit very loud) sound waves and converts that acoustic energy to picosecond-long flashes of light from bubbles excited to thousands of degrees, if not much hotter. Stranger still, the jitter from one flash to the next cycle is also on the scale of tens of picoseconds, even though the only thing providing the timing is a kilohertz-scale continuous sound wave. Very odd.

Even odder is the example of pyroelectricity. You take a normal ferroelectric crystal, and heat it up and cool it down over time scales of minutes... and it spits out X-rays and relativistic electrons! This is deeply weird. It's like you're crumpling and uncrumpling a piece of paper and every once in a while it emits a thunderclap: the energy scale is just completely wrong for what goes in versus what comes out.

Putterman and others have investigated these phenomena from the point of view of trying to harness them for sparking off tabletop fusion, with some success. Any time you have a normal continuous-media process providing you with easy access to high energies, you want to see how you can exploit that to leapfrog yourself to other high-energy processes such as nuclear reactions. But for me, I was happy to just bask in the weirdness of physics for a little while, and revel in the fact that nature can still surprise me in wonderful ways. There are some deep questions waiting to be answered here...