At the aptly named Photography Playground in Berlin, two artists run a “laboratory for water sound images,” which is basically a fancy way of saying they film ripples in water. There really isn’t much “laboratory” going on, as their work essentially just confirms age-old physical truisms, in this case that both water and air are, in a physics sense, fluids.In fact, the only difference between them is density, and as such they should both react similarly to similar forces. So, where compression waves in air will form patterns we perceive with our ears, water will form nearly identical patterns — but these we can perceive with our eyes.As you can see in the video above, these efforts can produce incredible images that transcend their simple origins. The water seems to dance along with the music — though maybe that says more about what dance really is than it does about water.What’s really interesting about this video are the interference patterns produced by the fact that the vat is so small; when the waves reflect off of the walls and bounce back, they can form complex standing wave patterns that are truly breath-taking. The creators point out that the patterns often resemble those found in nature, things like the arrangement of flower petals, the pattern of a turtle’s shell, or the bulbous forms of cell division. That’s all very interesting and philosophically intriguing, but these are still just pretty pictures.If you doubted the universality of the principles at work here (or if you just want to see more cool sound stuff) then consider a Ruben’s Tube: a simple tube lined with evenly spaced holes and filled with a flammable gas-air mixture. Cap one end with a speaker, the other with a, uh, cap, and light the gas coming out of the holes — as you’ll see, we don’t necessarily need water to visualize sound.Just as the compression and expansion of waves in water will force the liquid up into ridges (ripples) on the surface, the same forces in the gas within the tube either squirt the gas out more violently, or suck it back down. The result is a dynamic visualization of the shape of a sound wave — in fire! The coolest thing about a Rubens Tube, to me, is that the size of the fire-wave is the literal wavelength of the sound; this is not a metaphor for sound, but the real, actual size and shape of the wave itself.