Re: Speed of Light article

["Paul O. Johnson" <pojhome@SWBELL.NET>]

----- Original Message -----
From: "William Beaty" <billb@ESKIMO.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, June 01, 2000 12:41 PM
Subject: Re: Speed of Light article


> 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

The article Ken Fox referred to in the Denver Post is, indeed, the one
written by James Glanz in the NY Times on 30 May. The headline is "Light
Exceeds Its Own Speed Limit, or Does It?" I accessed it without registering
by clicking on the URL William provided. The heart of Glanz's story is:

"As most physicists interpret the experiment, it is a low-intensity
precursor (sometimes called a tail, even when it comes first) of the
incoming wave that clues the cesium chamber to the imminent arrival of a
pulse. In a process whose details are poorly understood, but whose effect in
Dr. Wang's experiment is striking, the cesium chamber reconstructs the
entire pulse solely from information contained in the shape and size of the
tail, and spits the pulse out early.

If the side of the chamber facing the incoming wave is called the near side,
and the other the far side, the sequence of events is something like the
following. The incoming wave, its tail extending ahead of it, approaches the
chamber. Before the incoming wave's peak gets to the near side of the
chamber, a complete pulse is emitted from the far side, along with a
backward wave inside the chamber that moves from the far to the near side.

The backward wave, traveling at 300 times c, arrives at the near side of the
chamber just in time to meet the incoming wave. The peaks of one wave
overlap the troughs of the other, so they cancel each other out and nothing
remains. What has really happened is that the incoming wave has "paid back"
the cesium atoms that lent energy on the other side of the chamber.

Someone who looked only at the beginning and end of the experiment would see
only a pulse of light that somehow jumped forward in time by moving faster
than c.

'The effect is really quite dramatic,' Dr. Steinberg said. 'For a first
demonstration, I think this is beautiful.' "

I dunno, Ken. I think you'll have to admit to your colleagues that
physicists don't yet completely understand Mother Nature.

Paul O.  Johnson