The tractor beam is one of the staples of science fiction, and it's becoming closer and closer to a reality. Just last year, scientists at Singapore's Agency for Science, Technology and Research were "able to create backward motion of particles in but separate from a forward-moving beam." Now, two scientists in New York have built a tractor beam.
The difference is a tractor beam would be forward moving while pulling a particle backwards. Previous incarnations have been able to pick up objects and push them further, and the aforementioned one can pull on the particles but uses temperature to do so. This means it could never function in space.
The idea that a Bessel Beam could actually do this (because it puts out light in concentric rings and could presumably be designed to have a particle inside said beam emit photons that face away from the source i.e. having them pull on objects rather than push them) has been put forward, but it has never actually occurred.
Well David Ruffner and David Grier, researchers at New York University, projected two of these Bessel beams side by side and had them overlap, which created a pattern of bright and dark regions along the beam. The photons in the bright regions can be arranged so when its photons hit a particle, they knock into the next bright region. This creates a backward domino effect of sorts and pulls the object backwards, rather than pushing it forward.
It's a bit confusing, but it works because the beams are non-diffractive and self-healing. In other words, if obstructed, they can reform on the other side of an obstruction. They don't spread out or scatter. So a collision with something can cause some photons to pull back, rather than scatter wildly.
Of course, they weren't moving spaceships. Rather, microscopic silica spheres that were suspended in water. And they moved them 30 micrometers. But in the realm of creating a freaking tractor beam, this remains fairly impressive.
This set-up can also work in space.
"NASA contacted us," said Ruffner. "They were wondering, can we put this on a space probe and get dust from a comet?"
Well, not quite yet. But it's a good step in that direction.
Via New Scientist