Getting There Faster: Light's Speed Accelerated

By Deborah Zabarenko

WASHINGTON (Reuters) - Scientists using lasers and specially prepared atoms have managed to make a pulse of light exceed its own top speed of 186,000 miles per second, appearing to leave a laboratory tube before it had fully entered.

This feat might seem more like wizardry than physics to some scientists, who have long assumed that nothing in the universe could go faster than the speed of light in a vacuum.

But researchers at the NEC Research Institute found they could make pulses of light zoom through a tube at a much faster speed, with the peak of the pulse emerging from the tube 62 billionths of a second before the peak had entered.

``It looks as if you've done something magical ... but you can explain this based on physics. This is not a time machine,'' James Chadi, vice president of the institute's science division, said on Thursday in a telephone interview from Princeton, New Jersey.

The NEC team's findings, published in Thursday's issue of the journal Nature, do not contradict Albert Einstein's theory of relativity, in which the great 20th century physicist set the speed of light in a vacuum as the absolute maximum speed for the universe.

According to Einstein's theory of relativity, nothing with mass -- like people or things -- can ever go faster than light, the researchers noted. But something with no mass, like a packet of light waves known as a pulse, can.

``Our experiment is perfectly consistent with Einstein's theory of special relativity,'' said lead researcher Lijun Wang in a telephone interview. ``Precisely speaking, it is the speed of information transfer that is limited by the speed of light in a vacuum.''

Exiting before it enters?

All the necessary information about the pulse is contained in its tiny leading edge. As soon as this sliver of the pulse enters the chamber, the specially prepared atoms can begin making another, identical pulse at the chamber's far side.

This finding might have implications for telecommunications, Chadi said.

A telecommunications application may exist even though information cannot move any faster than the speed of light, and it usually moves much more slowly, according to Arthur Dogariu, one of the authors of the Nature paper.

``Information is basically pulses,'' Dogariu said by telephone. ``When you talk about the Internet and fiber optic communications, it's limited by how the pulses can move through the wires, by how many of them there are, how thick the wires are.

``If you can create the medium in which pulses propagate, it would allow them to go through faster as a packet of waves,'' he said.

Any such application will not occur soon, and Dogariu said the environment he and his colleagues created in their laboratory could be re-created in other labs but not in nature.

Researchers at the NEC lab created this medium by using lasers to specially prepare atoms of cesium gas inside a cylindrical chamber about 2.5 inches long, and then shooting pulses of light through it.

Wang said the laser pulse should be thought of as a group of undulating waves of light, with peaks and valleys.

Normally light would pass through a vacuum chamber of that length in 0.2 nanoseconds, or .2 billionths of a second. But the cesium atoms in the chamber shift the light pulse, making it zip through the chamber and exit 62 nanoseconds sooner, or more than 300 times earlier.

As soon as the leading edge of the pulse enters the chamber, the atoms start to reconstruct the pulse at the chamber's far side. This reconstructed pulse can then emerge from the far end of the chamber sooner than it would go through a vacuum.

The NEC Institute is funded by Japan-based NEC Corp., which makes computers and communications products.