Scientists make sound so loud it boils water

Illustration for article titled Scientists make sound so loud it boils water
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If you haven’t yet received the latest issue of the journal Physical Review Fluids, spoiler alert, it’s a doozy. In this edition of America’s favorite fluid dynamics publication, Stanford scientists published the results of an experiment they conducted using X-ray free-electron laser pulses in 14 to 30 μm diameter liquid water microjets—that instantly boil water. I don’t understand one percent of how the researchers did this, but I am in awe of sound so loud it boils water.

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Stanford attempts to put this in layman’s terms (thank goodness): X-ray lasers hit the water, producing a shockwave. The shockwave travels through the liquid creating copies of itself, a “shockwave train,” that switches between high and low pressure. “Once the intensity of underwater sound crosses a certain threshold, the water breaks apart into small vapor-filled bubbles that immediately collapse.” The pressure created by the shockwaves was just below this breaking point, suggesting it was at the limit of how loud sound can get underwater. To further contextualize, the sound produced is equivalent to “directing the electrical power of an entire city onto a single square meter,” and is greater than that of a rocket launch. So freaking cool!

We already know some amazing things that sound waves can do in liquids, including aging whiskey. As previously reported, a Washington D.C. mixologist has successfully sped up whiskey aging—turning a 9-year-aged whiskey into one that tastes like it’s been aged 20 years—by blasting it with sound waves for “about as long as you’d watch a TV show.” Again, no scientist here, but could we use these ultra-intense x-rays to age whiskey instantly? Then again, we definitely don’t want to vaporize the whiskey. Proceed with caution, science.

Kate Bernot is a freelance writer and a certified beer judge. She was previously managing editor at The Takeout.

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DISCUSSION

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Cayde-6's Unloaded Dice

So the particular technique is called “laser ablation.” Basically, you heat up something so quickly that the kinetic energy of the surface vaporizing, per Newton’s Third Law of Motion, sends a shockwave through the material. It’s the same technique they use in Inertial Confinement Fusion. However, if you don’t have access megawatt lasers, you can see a similar effect at home. Get a pan screaming hot, and flick some water droplets on it. The droplets skittering around are undergoing what’s called the Leidenfrost effect, which is what happens when a liquid starts to boil so rapidly that the vapor generates enough force to actually suspend the liquid in mid-air.

The process by which the bubbles form in the water jet is called “cavitation”. When the pressure wave caused by the laser passes by, there are oscillations of extremely high and extremely low pressure. During the low pressure periods, the vapor pressure of water (the pressure at which a material will neither evaporate nor condense at a given temperature) is higher then the pressure in the water jet, so small bubbles of water vapor form. When the cavities collapse, the temperature inside the bubbles can reach thousands of degrees, and under the right conditions, that energy can be dissipated as light that can be seen in a dark room. You can also see cavitation happening if you’ve ever seen bubbles forming off of a fully submerged boat propeller.