Mind Bomb 14: Sonoluminescence

Mind Bomb 14: Sonoluminescence

Light comes from many sources - the filaments in light bulbs, the pixels of computer screens, and of course, the stars of the universe. But have you ever heard of light made from sound? Such a phenomenon is known as sonoluminescence, and we have observed this since the early 20th century.

Light is created from exploding bubbles caused by cavitation in a liquid. Cavitation is a result of sound travelling through a liquid that is so intense that it rips the liquid apart, creating cavitation bubbles in the void. 

Think about shooting a bullet through water - when a bubble travels through water, it creates sound waves behind and around it. This creates negative pressure as water is ripped apart, which in turn creates tiny bubbles of vapor. When these bubbles collapse on itself, it creates a loud sound, an immense amount of heat, and light! 

In fact, the pistol shrimp and mantis shrimp have utilised the sound created from cavitation to stun its prey by snapping its overpowered claw at about 100km/hour! You can check out this effect in the video below by BBC's Earth Unplugged Youtube Channel.

No one is exactly sure as to how the light is created, but like not being aware of the method to a magic trick, this just makes the phenomenon all the more magical. However, it used to be hard to witness as the light created only lasts for about 0.0000000001 seconds. The bubbles are also very small, only about 1 micrometre. Of course, fueled by curiosity, scientists have already done enough in the labs to consistently observe and film this underwater "star" light. 

Using the term "star" is not exactly an exaggeration. When the bubbles collapses on itself, the heat created as a result of this can be 10 times hotter than the surface of the Sun, albeit for just a tiny instance.

However, only long periods of time, the damage from this heat is quite significant, as seen by the degradation of water propellers, which generates cavitation bubbles so frequently due to the speed in which the propellers rotate. Our world is truly magical. For those who want to dive into the mechanics on how sonoluminescene works, do check out this paper titled Sonoluminescence: Sound into Light by Seth J. Putterman.