Slow Light? Fast Light? E=MC²?
| 1) Scientists Bring Light to a
Halt |
Physicist Lee
Hau, heading a research team from the Rowland Institute for Science, announced
last year that his team reduced the speed of a beam of light down to one mile
per hour using super-cooled sodium atoms.
Now,
the same research team and another team from the Harvard-Smithsonian Center for
Astrophysics have brought light to a halt.
The Rowland-Harvard
team used a dispersion of chilled sodium gas to store a laser pulse within
electron orbitals. The gas is excited by another laser to promote
electromagnetically induced transparency. Once the test pulse of light is
within the medium, the transparency-inducing laser is cut off. The pulse
remains within the gas as excited electron orbital states. When the
transparency-inducing laser is turned back on, the pulse is reformed by
electrons dropping their excited orbitals. Restored light remains
representative of the original pulse characteristics for about one second
before stored orbitals begin to decay.
This technique may
lead to future applications processing information for quantum computers. In
itself, it's a curiosity, but if a modified process could be adapted to
crystalline structure, the potential for data storage might be significant,
particularly if the state of each crystal in a matrix could be electrically or
optically set and read as desired.
| 2) Light Goes Faster Than
C |
Numerous successful
experiments to exceed Einstein's constant C - the speed at which light
traverses a vacuum - have been set up using "gain tubes" or superluminal
propagation chambers.
In the diagram, a
pulse of light is fired at source A. At B, the pulse enters the superluminal
propagation chamber. Light exits the tube at C.
For a
given set of conditions, we assign a group velocity index of n(g). Our
chamber's speed of light propagation is v. The speed of light constant is c.
Time is T. Time @ location B is T1. Time at location C is T2. The length from B
to C is L.
Then v(g)=c/n(g) within the superluminal
tube.
Delta T=L/v(g)-L/c so Delta
T=(n(g)-1)L/c
n(g) is less than 1 whenever v exceeds c [faster than
Einstein's light speed in a vacuum], so (n(g)-1) is
negative.
So our Delta T [time]
from the entrance of light at B until the light exits at C is
negative.
The light pulse exits at C before it enters the tube
at B. Time flow is negative as the pulse propagates. This has been confirmed by
laboratory measurements.
An interesting
thought experiment would be to place a mirror with a pinhole at B, place a full
mirror at C, and allow the light to bounce back and forth while traveling
backwards in time. (Note: this is a standard gas laser layout except for the
source.)
If the output pulse occurs BEFORE the input source is
fired, can a sufficiently fast computer watch for an output pulse then decide
NOT to fire the source lamp? What would happen?
Is
this a sum of possibilities problem and how does a Copenhagen Interpretation,
i.e. the simultaneous universes view, deal with such time flow
problems?
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