Light pulled out of empty space

NewScientist reports:

YOU can get something from nothing - as long as you are moving close to the speed of light. The discovery confirms a 41-year-old prediction on how to pull energy from empty space and produce light.

The phenomenon relies on the long-established fact that empty space is not at all empty, but fizzing with particles that pop in and out of existence (see "Out of the ether: the changing face of the vacuum"). This is down to the laws of quantum mechanics, which say that even a vaccum cannot have exactly zero energy but must exhibit small fluctuations of energy. These fluctuations show themselves as pairs of short-lived particles.

The presence of these "virtual" particles, usually photons, has long been proved in experiments demonstrating the standard Casimir effect, in which two parallel mirrors set close together will feel a pull towards each other. ...

"This is a significant breakthrough," says Diego Dalvit, a physicist at the Los Alamos National Laboratory in New Mexico. The energy of virtual photons is cosmologists' best guess of what lies behind the dark energy that is causing the universe's expansion to accelerate. The experiment will "open possibilities for doing table-top experiments of cosmology", Dalvit says.

Everyone agrees that empty space is not empty, but they are not sure what to call it. Here is a recent interview of this year's Nobel prizewinner:

GROSS: So does this finding challenge the law of gravity?

PERLMUTTER: There are a couple of ways that people are trying out to explain what's going on. Why is it that the universe is expanding faster and faster? Some of them involve considering a new energy that could be spread throughout all of space. And we're calling it dark energy for the moment as a placeholder, just because we don't yet know what its properties are.

If that is the explanation, then most of the universe is actually made up of this dark energy that we've never previously studied. ...

GROSS: So when you say it's three-quarters of the universe, is it the space between planets and galaxies?

PERLMUTTER: This dark energy, if that turns out to be the right explanation, is thought to be an energy that's associated with all of empty space. Any space at all in the universe would have some of this energy that's basically making space want to reproduce itself faster and faster, that's making, you know, our universe expand at an accelerated rate.

The best name for what permeates empty space is the luminiferous aether. It is an old-fashioned term, whose popularity might have peaked with J.C. Maxwell's 1878 encyclopedia article on it. It is an outstanding explanation of the pre-relativity aether. He speculates about the mass and energy of empty space, and today's aether is the logical descendant of Maxwell's.