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The Learning Kingdom's Cool Fact of the Day for July 20, 1999
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When does light travel slower than sound?
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Usually, light zooms through space at 300 million meters (186,000
miles) per second. But in a recent experiment, a pulse of light was
slowed down to only 17 meters (55.7 feet) per second. Sound travels
at 340 meters (1115 feet) per second in air.
The trick was to pass the light pulse through a cloud of extremely
cold sodium atoms. The sodium atoms, which were cooled to a frigid
50 billionths of a degree above absolute zero, entered a special
state called a "Bose-Einstein condensate." In this state, millions
of atoms act as if they are one single atom.
The light pulse slowed down because it constantly exchanged energy
with the atoms in the cloud. Upon leaving the cloud, it returned to
its normal zippy pace. Scientists are excited by the experiment's
implications for physics. It might also lead to new components for
optical computers or other devices.
The experiment was conducted by Dr. Lene Hau at the Rowland Institute:
http://dustbunny.physics.indiana.edu/~dzierba/P360/Week13/light/
story.html
http://www.sciencedaily.com/releases/1999/02/990223083631.htm
A Cool Fact about how Bose-Einstein condensates are formed:
http://www.cool-fact.com/archive/1997/10/16.html
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