One reason physics is so exciting is that whenever you think we know a fair bit about the universe, you can find a new phenomenon where no one has a clue about what’s going on. Some of these you don’t even hear about much, because there are only so many ways journalists can cover the “scientists still scratching their heads” angle of a story. That's is a shame because enduring mysteries can be the most fascinating.
One of the mysteries that fascinates me is a phenomenon called sonoluminesence. Imagine you take a vial of liquid and run sound waves through it intense enough to create a bubble, a process called cavitation. Since the newly formed bubble is a very low-pressure area in the middle of the higher pressure of the liquid, it will quickly collapse. As the bubble bursts, crazy, inexplicable stuff happens. First, the interior of the bubble gets insanely hot. Laboratories have measured the center of the bubble at thousands of degrees, with recorded temperatures going as high as 20,000° Celsius. (To compare, the surface of the sun is only 6,000 degrees Celsius.) At the same time, you can detect a flash of light in the center of the bubble—usually bluish in color—lasting for just a few trillionths of a second. This flash of heat and light is sonoluminesence.
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