Last May, researchers from the University of Dundee in Scotland proved that creating a tractor beam with sound was possible. This 10-minute video, recently posted by YouTube user whentheappledrops tries to simplify the science behind this discovery and suss out a definitive answer to the question: is this really possible?
As is true with many of these fantastical sci-fi claims, the answer is actually yes but with a few caveats. As the video explains:
If you focus a beam of light, it makes a shape similar to a diabolo...it turns out if you focus this shape on a particle, it does this thing called optical trapping. What happens is transparent particles get stuck in this optical trap because momentum is imparted to them by the photon...we can pull this object toward us.
The biggest exception there being this is all happening on a millimetre scale and doesn't look anything like this:
Resistance is definitely not futile.
But the most interesting discovery isn't so much that the science is possible, but that light may not be the best medium for creating a tractor beam. The problem is the more energy you put into scaling-up a light-based tractor beam, the more likely your are to engulf your target in extreme heat. That's why sound begins to make a lot more sense.
Instead if we think about using sound, suddenly we have a lot more room to work. Sound moves at a much lower rate, so it requires much lower energies to move things around...in theory, this doesn't have the same limitation because you can dump much more power in before you start doing biological harm to something with acoustic waves.
The video goes on to explain that scientists have discovered ways to apply torque to light and sound, allowing for waves to be manipulated into a twisting motion, much like a screwdriver, for instance.
Unfortunately, all future acoustic applications of a sonic tractor beam will be terrestrial-based since space is a vacuum. But maybe we should first build the Enterprise before we worry about anything else. [YouTube]