Re: Speed of Light article

[William Beaty <billb@ESKIMO.COM>]

On Wed, 31 May 2000, SSHS KPHOX wrote:

> The Denver Post ran an article about light passing through Cesium at
> speeds well in excess of c. They say it does not undermine the tenet's on
> relativity but I still do not understand it. Can anyone help me? My
> departmetn colleagues assumed I could enlighten them.

It must be the same as this one:

  NYT article (registration required)
  http://www.nytimes.com/library/national/science/053000sci-physics-light.html

This is NOT the old phase/group velocity misunderstanding.  The results
described in the article look suspiciously like a genuine violation of
relativity, as well as an example of a "time machine."

Briefly: they send a short pulse of light through a laser amplifier (the
cesium atoms mentioned.)  Rather than amplifying it, the laser does
something very weird.  The pulse comes out of the amplifier 60nS BEFORE
the original pulse goes in, while inside the amplifier a similar pulse
travels backwards at 300c and annhilates the incoming pulse.  The
investigators say that a low-level precursor wave precedes the actual
pulse, and this triggers the creation of the outgoing pulse and explains
the apparent causality violation. The shape of the outgoing pulse is the
same as the shape of the incoming pulse, and the phenomenon only works
across a narrow band of frequencies.

Another suspicious claim: they say that the outgoing pulse could not be
used to switch off the incoming pulse (and create a time paradox,) since
the electronics which could perform this feat would be too slow.  Huh?
Why would they say that???  If the phenomenon has a conventional
explanation, then why would they worry about the situation where the
incoming pulse is halted after the outgoing pulse has already left the
amplifier?

They do note that 60nS translates to 60 feet in air.  The outgoing pulse
is 60ft beyond the amplifier at the time that the incoming pulse starts to
enter the amplifier.  Weird!

The question that springs to my mind is this: was this phenomenon
predicted in advance, and then verified experimentally?  Or was it
stumbled upon, and only after the fact did they try to come up with an
explanation?  If the former, then their results might be genuine.  But if
the latter, then something fishy might be going on.  Perhaps causality and
relativity is actually being violated, and they are desparately trying to
"explain it away."  Or perhaps their measurements are bogus in the first
place, and nobody else will be able to reproduce their results.

Rudy Rucker, the mathematician and SF author, wrote an SF short story
where a scientist sends a little motor-driven toy through a block of
exotic matter, and the toy comes out of the far end BEFORE it starts to
enter the near end.  The guy grabs the toy in order to create a time
paradox, but instead of seeing a paradox he ends up developing two heads,
one of which decided to perform the experiment and the other which did
not.   :)


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