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There's no such thing as empty space

A team of scientists says an experiment in which tiny parcels of light are produced out of empty space has confirmed that a vacuum is not empty and that it contains quantum fluctuations of energy.

india Updated: Nov 19, 2011 12:10 IST

Scientists claim to have produced particles of light out of vacuum, proving that space is not empty.

An international team says that its ingenious experiment in which tiny parcels of light, or photons, are produced out of empty space has confirmed that a vacuum contains quantum fluctuations of energy, the Nature journal reported.

In fact, the scientists have demonstrated for the first time a strange phenomenon known as the dynamical Casimir effect, or DCE for short.

The DCE involves stimulating the vacuum to shed some of the myriad "virtual" particles that fleet in and out of existence, making them real and detectable. Moreover, the real photons produced by the DCE in their experiment collectively retain a peculiar quantum signature that ordinary light lacks.

The research, led by Chris Wilson of Chalmers University of Technology in Sweden, shows that a related dynamic effect can occur when such a mirror moves very fast through the vacuum. The DCE was predicted over 40 years ago, but had not yet been observed experimentally due to the difficulty of creating the required experimental conditions.

"The DCE was conceived as a kind of thought experiment, sort of like Schrodinger's Cat. According to quantum theory, if one could accelerate a mirror very quickly to near the speed of light, the mirror would radiate light as some of the mirror’s motional energy is imparted to virtual photons lurking in the vacuum, converting them into real photons.

"But it is practically impossible to accelerate a massive mirror to such high velocities. The required accelerations would be greater than the kind of shocks found in supernova or nuclear weapons explosions," said team member Prof Tim Duty.

Instead, the scientists set out to demonstrate the DCE using microwaves, like those used for mobile phone and wireless communication signals. And instead of a massive mirror, they used a tiny microcircuit called a Superconducting Quantum Interference Device, or SQUID.

The SQUID acts as a tunable mirror for virtual microwave photons, fooling them into behaving as if they encountered a moving mirror when in fact nothing is physically moving.

Furthermore, they had to cool the experiment to a small fraction of a degree above absolute zero in order to get rid of unwanted thermal microwaves that would mask the DCE.

"The fact that the quantum vacuum is not empty, as demonstrated in our experiment, is related to lots of other interesting effects such as Hawking radiation of black holes and the Lamb shift in atomic physics," Prof Duty said.