Of all the puzzling physical effects predicted and explained by quantum mechanics, one of the most counterintuitive is that fluctuations in a vacuum can exert forces on objects—almost as if those objects are getting something from nothing. Even in empty space, there are flutterings of energy, and sometimes those tiny ripples act in demonstrable ways. One example is known as the Casimir effect, predicted to exist in 1948 by the late Dutch physicist Hendrik Casimir, in which quantum fluctuations create an attractive force between two surfaces in a vacuum.

A group of researchers report in the online edition of Nature that they demonstrated for the first time the repulsive version of this quantum effect. Their results show that by judiciously choosing two materials (silica and gold) immersed in a fluid (bromobenzene), quantum fluctuations can be seen to drive the materials apart. This repulsive version of the Casimir effect had long been predicted but never observed.

Lead author Jeremy Munday, now a postdoc in physics at the California Institute of Technology, says that his team's research may lend itself to producing ultrasensitive detectors and almost friction-free devices by separating their components via Casimir repulsion.

"Where you would normally have friction," he says, "you can start to greatly reduce that by having a repulsive interaction that doesn't let the surfaces come into contact."

More generally, a greater understanding of the Casimir effect and how to manipulate it should benefit engineers working at the nanoscale. Although commercially available devices are not yet small enough to be greatly troubled by the Casimir effect, Munday says, it will start to come into play as they continue to shrink.

"As people are trying to push the envelope to get smaller and smaller devices, then you have to start worrying about that," Munday says. "Because whenever you have a moving structure, and it comes within tens or hundreds of nanometers of another solid structure, then the Casimir force will start to interact there. And so that changes the way you're going to design a device."

Image credit: Jay Penni and Federico Capasso