Calling forth light from the void was once an act of biblical proportions. Now all it takes is a bit of smoke and mirrors provided by the laws of quantum mechanics.
By creating particles of light from seeming nothingness, an international team of researchers has confirmed an idea first proposed in 1970.
According to quantum physics, empty space isn’t actually empty. Even a vacuum contains energy, tiny fluctuations that can be thought of as virtual waves or virtual particles flitting in and out of existence.
These fluctuations exert a force. Put two mirrors close together in a vacuum, and some of the virtual waves will be too long to fit between them. A pressure — analogous to the pressure that crumples a water bottle with some of its air sucked out — pushes the mirrors toward each other. This static Casimir effect already has been measured by several scientists.
But like Pinocchio, the virtual particles long to become real. Their Blue Fairy is an accelerating mirror, which separates pairs of virtual particles and provides the energy needed to turn them into real particles of light, or photons. Christopher Wilson of the Chalmers University of Technology in Gothenburg, Sweden, and colleagues now claim to have produced such photons for the first time.
“We expect this effect, the dynamical Casimir effect, to be there,” says Larry Ford, a theoretical physicist at Tufts University in Medford, Mass., who was not involved in the research. “If it’s not there, that would be a problem. It’s important for quantum field theory.”
A mirror wobbling back and forth should start to sparkle with photons. But to create a detectable number of photons, the mirror would have to move at a significant fraction of the speed of light — which just isn’t practical.
“The required accelerations are beyond the types of shocks one encounters in supernova and nuclear weapons explosions,” says Yale physicist Steve Lamoreaux, who was one of the first to accurately measure the static Casimir effect.
So instead of using a real mirror, Wilson’s team built a circuit called a SQUID, or superconducting quantum interference device. The team exposed a loop of metal to a magnetic field that fluctuated about 11 billion times per second. The loop wobbled electrically — much like a mirror wobbling at 5 percent of the speed of light — and nudged the virtual particles in the vacuum.
Photons appeared in a special state called two-mode squeezing, a quantum signature of particles created in pairs. Wilson and his colleagues reported their experiment in a paper posted online May 24 at arXiv.org, but they declined an interview request, citing policies of a journal now reviewing the research for publication.
“This is great work, probably one of the best Casimir papers in the last 40 years,” says Lamoreaux.
The results should reassure scientists trying to detect Hawking radiation, energy predicted to be given off by black holes. The same quantum principles that give mirrors their extra sparkle should also make black holes glow.