This video shows a real live tractor beam in action. It uses an array of small speakers to levitate objects and to move them precisely through the air. The beam can even pull objects from above, just like the tractor beams that aliens spacecraft use to abduct human subjects for their terrifying experiments.
You’ve felt the blast from a giant bass speaker at a live concert or a club, so it’s easy to picture how a speaker can shape the air. By using lots of speakers, all working together, it’s possible to build an “acoustic trap.” The sounds waves from the speakers each interfere with each other, and if you tune them just right, you can produce a pocket of still air in which an object can sit. “We characterize a 3-D trap as a point towards which the forces converge from all directions,” says the paper, from researchers at the University of Bristol in the U.K. “The traps are strong enough to hold the spheres and counteract gravity from any direction.”
By further manipulating the sound, this the object can be moved. As you can see in the video, this is a precise movement, not a bouncy, lurching action. In fact, the method is precise enough that it can be used to make “acoustic tweezers,” which can maneuver an object precisely enough for use on production lines, for example.
This work brings the advantages of optical tweezing (that is, single-beam, rotation, holographic control and multiple particles) 24 to the efficiency and versatility of acoustic levitation and could lead to the development of powerful tractor beams, 3-D physical displays or acoustically controlled in vivo micro-machines that do not interfere with magnetic resonance imaging.
The novelty in Bristol University’s tractor beam is that it pushes and pulls from one side. Previous sonic grapplers use at least two sides, to sandwich the objects between them.
The obvious uses for a tractor beam are for moving objects around, or making amusing store-window displays, or dragging Corellian freighters inside Star Destroyers. But the authors note that larger versions could be used to shift bigger objects through 3-D space–in warehouses, for example. Even more interesting is that the tractor beam can be fired through human flesh:
[These] devices potentially enable in vivo manipulation since the device could be applied directly onto the skin with the manipulation taking place inside the body; similar to an ultrasound scanner but for manipulating particles (that is, drug capsules, kidney stones or micro-surgical instruments).
Maybe the whole alien abduction/medical experimentation schtick isn’t so far-fetched after all.