Sonoluminescence is a mysterious phenomenon caused when ultrasonic waves excite a liquid, creating small bubbles that emit light as they collapse. The effect is magnified when the bubbles contain a noble gas. The term sonoluminescence means “sound light”.
There are various theories of sonoluminescence, none of which have finally emerged. Temperatures in excess of 20,000 K have been measured at the centers of these small bubbles. This is hot enough to cook diamond.
The phenomenon of sonoluminescence was popularized in the movie Chain Reaction star Keanu Reeves. In the film, sonoluminescence is used to kickstart a nuclear fusion reaction. The bubbles created by sonoluminescence have been observed to generate temperatures that measure in kilocalories or tens of thousands of degrees. The temperature threshold for starting nuclear fusion reactions is in the millions of degrees, or mega-wins. There is a bit of a discrepancy here, a discrepancy adding up to three orders of magnitude. Sonoluminescence is hot, but it’s not that hot.
Scientists from the laboratory of Purdue scientist RP Taleyarkhan argued that during sonoluminescence, an acetone-filled vessel releases neutrons at a statistically significant level, the characteristic footprint of fusion. However, these results have never been duplicated and were dismissed in an article in Nature in 2006. The Taleyarkhan patent for the device was rejected and an analysis was published by B. Naranjo showing that his data was misinterpreted.
The effect of sonoluminescence was first discovered by German scientists H. Frenzel and H. Schultes at the University of Cologne in 1934. They attempted to accelerate the process of developing images, but ended up observing luminous bubbles instead. Because the effect was so random and uncontrollable, it was not scientifically studied until much later.
In 1989, Felipe Gaitan and Lawrence Crum were able to create a bubble of sonoluminescence that stayed in a constant location – an ultrasonic standing wave periodically generated a bubble, and then collapsed. This was a major step forward, and it allowed the phenomenon to be analyzed in a laboratory setting. The bubbles were found to be very small when the light was released – about a micrometer wide, or about the size of a bacterium. The duration of the flashes of light is extremely short, although in aggregate they can be observed with the naked eye – each flash of light lasts a few tens to a few hundred picoseconds, the time it takes for the light to move a few centimeters.
Even sonoluminescence is an incredible effect, as it currently has no specific applications and will probably never be exploited for fusion power. Remarkably, there are shrimp that snap the claws so fast that they show sonoluminescence. Scientists with a sense of humor called this effect shrimpoluminescence.
- Sonoluminescence is caused when ultrasonic waves excite a liquid, creating small bubbles that emit light as they collapse.