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Watch the world’s most powerful tractor beam levitate its biggest catch

It’s a far cry from levitating a space ship—or even a human being—but a tractor beam armed with 192 loudspeakers has just levitated its heaviest catch yet: a 16-millimeter-wide Styrofoam ball. So-called sonic tractor beams use loudspeakers to create high-pressure shapes out of sound—acoustic holograms—that can hold, rotate, and move objects in midair. But for years researchers have struggled to levitate objects larger than half the wavelength of the sound. Using a single acoustic vortex created by a grid of 52 speakers, for example, researchers have only been able to raise objects up to 1.6 millimeters in diameter—larger items spin uncontrollably and are ejected. Now, a team of engineers has figured out how to levitate objects more than 10 times that size (above). Using 192 loudspeakers, the researchers created not one, but two vortexes that pulse in alternating bursts of a few milliseconds. This technique stops the objects spinning, which makes them more stable and lets them levitate objects larger than the wavelength of sound, they report this week in Physical Review Letters. It will still be some time before such beams can be put to practical use, but in the meantime researchers suggest that with more powerful speakers, they might be able to hold—and control—astronauts in zero gravity.