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starship-design: Light can break its own speed limit

Light can break its own speed limit, researchers say

July 20, 2000
Web posted at: 2:16 p.m. EDT (1816 GMT)
 In this story:   Not so impossible  Application: faster computers?  How the
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(AP) -- Scientists have apparently broken the universe's speed limit.
For generations, physicists believed there is nothing faster than light
moving through a vacuum -- a speed of 186,000 miles per second.
But in an experiment in Princeton, New Jersey, physicists sent a pulse of
laser light through cesium vapor so quickly that it left the chamber before
it had even finished entering.
The pulse traveled 310 times the distance it would have covered if the
chamber had contained a vacuum.
Researchers say it is the most convincing demonstration yet that the speed
of light -- supposedly an ironclad rule of nature -- can be pushed beyond
known boundaries, at least under certain laboratory circumstances.

Not so impossible

"This effect cannot be used to send information back in time," said Lijun
Wang, a researcher with the private NEC Institute. "However, our experiment
does show that the generally held misconception that `nothing can travel
faster than the speed of light' is wrong."
The results of the work by Wang, Alexander Kuzmich and Arthur Dogariu were
published in Thursday's issue of the journal Nature.
The achievement has no practical application right now, but experiments like
this have generated considerable excitement in the small international
community of theoretical and optical physicists.
"This is a breakthrough in the sense that people have thought that was
impossible," said Raymond Chiao, a physicist at the University of California
at Berkeley who was not involved in the work. Chiao has performed similar
experiments using electric fields.
In the latest experiment, researchers at NEC developed a device that fired a
laser pulse into a glass chamber filled with a vapor of cesium atoms. The
researchers say the device is sort of a light amplifier that can push the
pulse ahead.
Previously, experiments have been done in which light also appeared to
achieve such so-called superluminal speeds, but the light was distorted,
raising doubts as to whether scientists had really accomplished such a feat.
The laser pulse in the NEC experiment exits the chamber with almost exactly
the same shape, but with less intensity, Wang said.
The pulse may look like a straight beam but actually behaves like waves of
light particles. The light can leave the chamber before it has finished
entering because the cesium atoms change the properties of the light,
allowing it to exit more quickly than in a vacuum.
The leading edge of the light pulse has all the information needed to
produce the pulse on the other end of the chamber, so the entire pulse does
not need to reach the chamber for it to exit the other side.
The experiment produces an almost identical light pulse that exits the
chamber and travels about 60 feet before the main part of the laser pulse
finishes entering the chamber, Wang said.
Wang said the effect is possible only because light has no mass; the same
thing cannot be done with physical objects.
The Princeton experiment and others like it test the limits of the theory of
relativity that Albert Einstein developed nearly a century ago.
According to the special theory of relativity, the speed of particles of
light in a vacuum, such as outer space, is the only absolute measurement in
the universe. The speed of everything else -- rockets or inchworms -- is
relative to the observer, Einstein and others explained.

Application: faster computers?

In everyday circumstances, an object cannot travel faster than light. The
Princeton experiment and others change these circumstances by using devices
such as the cesium chamber rather than a vacuum.
Ultimately, the work may contribute to the development of faster computers
that carry information in light particles.
Not everyone agrees on the implications of the NEC experiment.
Aephraim Steinberg, a physicist at the University of Toronto, said the light
particles coming out of the cesium chamber may not have been the same ones
that entered, so he questions whether the speed of light was broken.
Still, the work is important, he said: "The interesting thing is how did
they manage to produce light that looks exactly like something that didn't
get there yet?"

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