Tractor beams are one of those sci-fi staples that, when you get right down to it, are actually pretty hard to wrap your head around: it's a force that projects outward, and yet it pulls an object inward. Crazy as it is, Chinese researchers may have just figured out how to do just that.
Before you look to China for all your future cow abduction conspiracy theories, the beam that the researchers at Fudan University in Shanghai have going works on the nanoscopic level. How'd they do it? Well, in the simplest terms, they turned a laser beam inside out, which, according to Popular Science, "should generate a backward pulling force from a forward traveling stream of photons."
Of course, like any awesome technology in its infancy, there's still a laundry list of "buts." For one, the conditions whereby the beam operates flawlessly are rather particular, and even the smallest deviation from the beam's optimal environment could throw it off. That, and at its tiny scale, you won't see China tractorin' anything all that large — unless this technology upscales surprisingly well. That said, it could be an amazingly useful tool on a smaller scale, especially with, say, medical nanotech.