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- 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 299,000 kilometres a second.
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- But in an experiment in Princeton, N.J., physicists sent
a pulse of laser light through cesium vapour so quickly it left the chamber
before it had even finished entering.
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- The pulse travelled 310 times the distance it would have
covered if the chamber had contained a vacuum.
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- Researchers said 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.
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- ''This effect cannot be used to send information back
in time,'' said Lijun Wang, a researcher with the private NEC Institute.
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- ''However, our experiment does show that the generally-held
misconception that `nothing can travel faster than the speed of light'
is wrong.''
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- The results were published in Thursday's issue of the
journal Nature.
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- Not everyone is convinced the NEC scientists did what
they claim.
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- 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.
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- 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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- 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.
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- ''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.
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- In the latest experiment, researchers at NEC developed
a device that fired a laser pulse into a glass chamber filled with a vapour
of cesium atoms. The researchers said the device is sort of a light amplifier
that can push the pulse ahead.
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- 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.
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- The laser pulse in the NEC experiment exits the chamber
with almost exactly the same shape but with less intensity, Wang said.
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- 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 trade energy with
the leading edge of the waves as they pass through.
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- This produces an almost identical light pulse that exits
the chamber and travels about 18 metres before the main part of the laser
pulse finishes entering the chamber, Wang said.
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- Wang said the effect is possible only because light has
no mass; the same thing cannot be done with physical objects.
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- The Princeton experiment and others like it test the
limits of the theory of relativity Albert Einstein developed nearly a century
ago.
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- The special theory of relativity states 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.
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- In everyday circumstances, an object cannot travel faster
than light.
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- The Princeton experiment and others change these circumstances
by using devices such as the cesium chamber, rather than a vacuum.
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- Ultimately, the work may contribute to the development
of faster computers that carry information in light particles.
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