WC Archive

It's one of those assertions that a reasonable person might immediately dismiss -- sound waves can make bubbles in liquid blow up in such a way that they produce temperatures and pressures equivalent to the inside of the sun. But sonoluminescence is a well-known phenomenon (here is an intro to the subject from Lawrence Livermore National Laboratories); since 1934, physicists have known that pulsing low-density sound waves through a liquid medium can causes flashes of light. Now, a group of physicists at Purdue university have concluded that, under the right conditions, pulsing sound through liquid can result in sufficient energy to produce nuclear fusion.

The device is a clear glass canister about the height of two coffee mugs stacked on top of one another. Inside the canister is a liquid called deuterated acetone. The acetone contains a form of hydrogen called deuterium, or heavy hydrogen, which contains one proton and one neutron in its nucleus. Normal hydrogen contains only one proton in its nucleus.

The researchers expose the clear canister of liquid to pulses of neutrons every five milliseconds, or thousandths of a second, causing tiny cavities to form. At the same time, the liquid is bombarded with a specific frequency of ultrasound, which causes the cavities to form into bubbles that are about 60 nanometers - or billionths of a meter - in diameter. The bubbles then expand to a much larger size, about 6,000 microns, or millionths of a meter - large enough to be seen with the unaided eye.

"The process is analogous to stretching a slingshot from Earth to the nearest star, our sun, thereby building up a huge amount of energy when released," Taleyarkhan said.

Within nanoseconds these large bubbles contract with tremendous force, returning to roughly their original size, and release flashes of light in a well-known phenomenon known as sonoluminescence. Because the bubbles grow to such a relatively large size before they implode, their contraction causes extreme temperatures and pressures comparable to those found in the interiors of stars. Researches estimate that temperatures inside the imploding bubbles reach 10 million degrees Celsius and pressures comparable to 1,000 million earth atmospheres at sea level.

There are still plenty of questions about the discovery, but the paper reporting the work apparently went through a far greater-than-usual checking process at Physical Review E, where it will be published. Unlike Cold Fusion, the sonofusion work seems to have both good data and an explanation for the mechanism that doesn't require rewriting any physical laws. Skeptics are (quite correctly) waiting for other labs to be able to replicate the experiment before celebrating the find.

Assuming the discovery is validated, what does it mean for the world? At minimum, much more work. The sonofusion research is still in the earliest of stages, and requires much more power to produce the effect than is produced -- the so-called "breakeven" level required for fusion energy to be useful. Even if breakeven is achieved, there's no guarantee that it could scale to a point where it would be competitive with other methods.

But what this discovery does do right now is provide us with a friendly reminder that we can't assume that all the tools we'll have for fighting global problems have already been invented. New discoveries, new technological or social innovations add to our response capabilities. While we certainly shouldn't assume that a deus ex machina is going to save us all, neither should we despair that our current abilities are insufficient for the task at hand.