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Light "Stopped in its tracks"

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I just re-noticed this press release I received a couple of days ago from NASA. As the speed of light has been a topic here a few times, I thought that some of you might find this interesting. I will try to comment on this later.





NASA-funded research at Harvard University, Cambridge,

Mass., that literally stops light in its tracks, may someday

lead to breakneck-speed computers that shelter enormous

amounts of data from hackers.


The research, conducted by a team led by Dr. Lene Hau, a

Harvard physics professor, is one of 12 research projects

featured in a special edition of Scientific American

entitled "The Edge of Physics," available through May 31.


In their laboratory, Hau and her colleagues have been able

to slow a pulse of light, and even stop it, for several-

thousandths of a second. They've also created a roadblock

for light, where they can shorten a light pulse by factors

of a billion.


"This could open up a whole new way to use light, doing

things we could only imagine before," Hau said. "Until now,

many technologies have been limited by the speed at which

light travels."


The speed of light is approximately 186,000 miles per second

(670 million miles per hour). Some substances, like water

and diamonds, can slow light to a limited extent. More

drastic techniques are needed to dramatically reduce the

speed of light. Hau's team accomplished "light magic" by

laser-cooling a cigar-shaped cloud of sodium atoms to one-

billionth of a degree above absolute zero, the point where

scientists believe no further cooling can occur. Using a

powerful electromagnet, the researchers suspended the cloud

in an ultra-high vacuum chamber, until it formed a frigid,

swamp-like goop of atoms.


When they shot a light pulse into the cloud, it bogged down,

slowed dramatically, eventually stopped, and turned off. The

scientists later revived the light pulse and restored its

normal speed by shooting an additional laser beam into the



Hau's cold-atom research began in the mid-1990s, when she

put ultra-cold atoms in such cramped quarters they formed a

type of matter called a Bose-Einstein condensate. In this

state, atoms behave oddly, and traditional laws of physics

do not apply. Instead of bouncing off each other like bumper

cars, the atoms join together and function as one entity.


The first slow-light breakthrough for Hau and her colleagues

came in March 1998. Later that summer, they successfully

slowed a light beam to 38 miles per hour, the speed of

suburban traffic. That's two million times slower than the

speed of light in free space. By tinkering with the system,

Hau and her team made light stop completely in the summer of



These breakthroughs may eventually be used in advanced

optical-communication applications. "Light can carry

enormous amounts of information through changes in its

frequency, phase, intensity or other properties," Hau said.

When the light pulse stops, its information is suspended and

stored, just as information is stored in the memory of a

computer. Light-carrying quantum bits could carry

significantly more information than current computer bits.

Quantum computers could also be more secure by encrypting

information in elaborate codes that could be broken only by

using a laser and complex decoding formulas.


Hau's team is also using slow light as a completely new

probe of the very odd properties of Bose-Einstein

condensates. For example, with the light roadblock the team

created, they can study waves and dramatic rotating-vortex

patterns in the condensates.


The Harvard research team includes Hau; Drs. Zachary Dutton,

Chien Lieu, Brian Busch and Michael Bu

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Yes, but only under controlled conditions. This does not upset Einstein's theory that the speed of light is constant, for that only applies to light in a vacuum (although that theory is being debated, the VSL theory). This does NOT mean that we will be able to slow the speed of light in say normal air. It will remain a constant (at STP). What it does mean is that through certain types of matter, under certain conditions we can slow (and apparently stop) light.


Just my .02 cents



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