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Fwd = [UASR]> Putting the brakes on light

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  • Frits Westra
    Forwarded by: fwestra@hetnet.nl Originally from: Lieve Original Subject: [UASR] Putting the brakes on light Original Date: Sat, 26 Feb
    Message 1 of 1 , Feb 26, 2000
      Forwarded by: fwestra@...
      Originally from: Lieve <SHADO@...>
      Original Subject: [UASR]> Putting the brakes on light
      Original Date: Sat, 26 Feb 2000 13:10:55 -0800

      ========================== Forwarded message begins ======================

      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.

      Slow light

      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
      slow down.

      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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