Fwd = [UASR]> Putting the brakes on light
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Originally from: Lieve <SHADO@...>
Original Subject: [UASR]> Putting the brakes on light
Original Date: Sat, 26 Feb 2000 13:10:55 -0800
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[U A S R]> UFO's-, ALIEN's-, SPACE- RESEARCH MAILING LIST <[U A S R]
Thursday, 24 February, 2000, 16:11 GMT
Putting the brakes on
BY BBC News Online science editor
Dr David Whitehouse
You think that light is fast? Well
think again, sometimes it is slower
that a crawl.
All schoolchildren know that light is
the fastest thing there is, zipping
along through empty space at
297,000 km per second (186,000
miles a second). Light from the Sun
takes about eight minutes to reach
us, from the Moon just over a second
and 2 million years from the nearest
But now a Danish physicist and her
team of collaborators have found a
way to slow light down to less than
one mile an hour (1.6 km per hour),
slower than a slow walk.
The researchers led by Dr. Lene Hau,
of the Rowland Institute for Science
and Harvard University, said last year
that they had slowed light down to
38 mph (60 km per hour). Now they
have gone even further.
Addressing a conference in the United
States she said that you can almost
send out a beam of light, go for a cup
of coffee and return in time to see
the light come out of the other side
of her equipment. "You could almost
touch it," she added.
The way Dr. Hau and her team have
slowed down light by a factor of 600
million or so is to use a group of
atoms called a "Bose-Einstein
condensate (BEC)." These atoms are
cooled to a temperature of only a few
billionths of a degree above absolute
zero, the coldest possible
temperature, at which all motion
In a Bose-Einstein condensate atoms
are hardly moving at all. This means
that according to the uncertainty
principle that rules atoms they are
spread out and overlap. This results
in a group identity for the collection
of supercold atoms.
And in such a superatom light will
Physicists have known for a long time
that the speed of light is reduced
when it travels though any
transparent medium, such as water or
glass. Lenses, for example, focus
light by allowing it to pass through
different thicknesses of glass,
thereby slowing it down by differing
By firing co-ordinated beams of laser
light through the BEC the researchers
have slowed it down to a crawl.
Inside the BEC the so-called
refractive index (which measures the
slowing of light) of the atomic
condensate becomes enormous, as
high as 100 trillion times greater than
that of glass.
Slowing down light may have many
practical uses in communications,
signal processing, television displays
and night-vision devices.
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* Lieve Peten, Vlaanderen, Belgium : Mailto:shado@...
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