Under certain circumstances, sound waves can generate light. Find out which circumstances, explore the debate about how the phenomenon works, and learn how to make your own sonoluminescence generator.
The first instances of sonoluminescence were documented in the mid-nineteen-thirties, when scientists experimenting with naval sonar noticed that sound waves, when traveling through water, could sometimes create a bluish glow. Small bubbles would emit flashes of light in ways that could only be termed ‘aces'. As the thirties wore on scientists found that they had more important things on their minds than the study of mood lighting.
It wasn't until the late nineteen eighties, when the nuclear arsenals were good and stocked, and the popularity of neon clothing made bluish glowing things potentially big business. Scientists managed to repeatedly create single-bubble sonoluminescence; single bubbles that would glow with bluish bursts of light.
There are a few things about sonoluminescence that everyone agrees on. It happens because small bubbles are created, and because the sound waves applied to water cause those bubbles to expand and contract rapidly. That rapid expansion and contraction, in such a small space, causes a massive concentration of the energy of the sound waves causes the flashes of light. Most papers about sonoluminescence take pains to note that a ‘concentration of energy' is hardly a new concept. A concentration of energy occurs every time a person gets a static shock from a doorknob. The large difference in charge between the person and the doorknob gets concentrated on the tip of one finger and creates a shock. Other concentrations of energy can be even simpler. For example, the blade of a knife, as it cuts into something concentrates all the force of a cut into such a small area, that it can slice through pretty much anything, depending on the infomercial it is in.
What it is, exactly, that makes the flashes of light in sonoluminescence is up for debate. One of the most commonly held theories is the idea that when the bubble collapses, the air inside gets pressurized. Increasing the pressure on a gas increases the temperature of the gas. During sonoluminescence, the temperature inside the tiny bubbles becomes so great that the gas begins to glow.
Another theory is that the collapsing bubble lends energy to prolong the life of the otherwise quickly annihilating photons that are spontaneously generated in a vacuum. Io9 has done a piece on The Casimir Effect, which is the result of the spontaneous generation of these particles. Sonoluminescence could also be the product of the way photons can pop into and out of existence; the sudden collapse of the bubble making the photons noticeable to those in the macro world.
Those readers with an inquisitive turn of mind, and plenty of time on their hands, can create their own sonoluminescence generators by following instructions here.
Top image via Part_Man