Two German physicists first discovered that sound could actually be transformed into light more than 50 years ago, although they achieved sonoluminescence only erratically. Putterman, who specializes in continuum mechanics, especially acoustics, low-temperature physics and fluids, had never given the notion a thought until a colleague challenged him to explain how sound could be transformed into light. Putterman and one of his students took this as a dare and set about putting together their own makeshift sound-to-light system, using an oscilloscope, a sound generator and a home stereo amplifier.

The result can be seen in Putterman's lab. sitting in the dark and staring at a water-filled flask, you will see a tiny, faint blue speck of light, a remarkable, almost magical sight. In some ways, it is reminiscent of the light shows of the '60s, in which strobe lights were coordinated to the pulsating music. But those sound waves, of course, were not being converted into light waves, which is what is happening inside Putterman's flask.

As one of Putterman's students put it: "It's a star in a jar."

The "star" is actually a gas-filled bubble lit by a sound wave. As Putterman explains it, sound waves of about 110 decibels at a frequency just beyond the range of human hearing are sent through water. In the water is a small piece of toaster wire and, as a current is generated to heat it, the water nearly boils and forms an air bubble.

The bubble then becomes trapped in the center of the flask because the buoyancy force that would send it to the top is balanced by the force of the sound waves.

The demonstration is much more than a scientific sideshow. Putterman is a busy UCLA professor who must make time for research. born in Brooklyn, he earned his Ph.D. at Rockefeller University, then came to UCLA 25 years ago. The physicist admits that on "research days" he throws out unexpected mail—even Federal Express packages—if he doesn't recognize the sender's name. "As a scientist, I'm interested in my own curiosity," he says. "To accomplish research one must be single-minded."

The steady light Putterman has achieved has raised a raft of questions about the mechanism behind the phenomenon and sparked newfound interest in sonoluminescence among scientists around the country.

Besides determining the exact hows and whys of sonoluminescence—Putterman believes it's connected to the shock wave produced by the imploding air bubble—scientists are now trying to discover practical uses for it.

 "For one thing, this is a cheap source of pico-second flashes of light, which are used to study the fluorescent properties of molecules," says Putterman. "Our $200 apparatus will do what a $30,000 laser can do."

Researchers are also exploring other potential uses of collapsing bubbles, from delivering drugs to tumor sites via sound-light bubbles to testing whether concentrated sound can destroy toxic chemicals. The really big coup, though, would be if sonoluminescence could help produce nuclear fusion energy—a notion that is still highly speculative, and which is difficult to test because nature mysteriously doesn't provide stable sonoluminescence from bubbles filled with deuterium.

Putterman is confident sonoluminescence will bear practical fruit. In fact, he's already accomplished one goal just by raising interest. "A physicist needs to be well-grounded in the philosophy of science," he says. "Theories which do not have predictive value have no value. The best experiment is one that falsifies a clear theory. That's because when you disprove it, you raise questions—and we're always looking to raise questions."