Re: FTL transmission?

From: Michael S. Lorrey (
Date: Tue May 30 2000 - 20:56:50 MDT

Damien Broderick wrote:
> At 02:29 PM 30/05/00 -0400, Brian Atkins <>
> wrote:
> >
> This is not accessible to anyone outside the States - that is, we can't
> register.
> So what's the story about?
> Damien
>From the link above:
May 30, 2000

          Light Exceeds Its Own Speed Limit, or
          Does It?

          By JAMES GLANZ

               he speed at which light travels through
               a vacuum, about 186,000 miles per
          second, is enshrined in physics lore as a
          universal speed limit. Nothing can travel
          faster than that speed, according freshman
          textbooks and conversation at sophisticated
          wine bars; Einstein's theory of relativity
          would crumble, theoretical physics would
          fall into disarray, if anything could.

          Two new experiments have demonstrated
          how wrong that comfortable wisdom is.
          Einstein's theory survives, physicists say, but
          the results of the experiments are so mind-bending and weird
that the
          easily unnerved are advised--in all seriousness--not to read
beyond this

          In the most striking of the new experiments a pulse of light
that enters a
          transparent chamber filled with specially prepared cesium gas
is pushed
          to speeds of 300 times the normal speed of light. That is so
fast that,
          under these peculiar circumstances, the main part of the pulse
exits the far
          side of the chamber even before it enters at the near side.

          It is as if someone looking through a window from home were to
see a
          man slip and fall on a patch of ice while crossing the street
well before
          witnesses on the sidewalk saw the mishap occur--a preview of
the future.
          But Einstein's theory, and at least a shred of common sense,
seem to
          survive because the effect could never be used to signal back
in time to
          change the past--avert the accident, in the example.

          A paper on the experiment, by Lijun Wang of the NEC Research
          Institute in Princeton, N.J., has been submitted to Nature and
is currently
          undergoing peer review. It is only the most spectacular
example of work
          by a wide range of researchers recently who have produced
          speeds of propagation in various materials, in hopes of
finding a chink in
          Einstein's armor and using the effect in practical
applications like speeding
          up electrical circuits.

          "It looks like a beautiful experiment," said Raymond Chiao, a
          of physics at the University of California in Berkeley, who,
like a number
          of physicists in the close-knit community of optics research,
          knowledgeable about Dr. Wang's work.

          Dr. Chiao, whose own research laid some of the groundwork for
          experiment, added that "there's been a lot of controversy"
over whether
          the finding means that actual information--like the news of an
          accident--could be sent faster than c, the velocity of light.
But he said that
          he and most other physicists agreed that it could not.

          Though declining to provide details of his paper because it is
          review, Dr. Wang said: "Our light pulses can indeed be made to
          faster than c. This is a special property of light itself,
which is different
          from a familiar object like a brick," since light is a wave
with no mass. A
          brick could not travel so fast without creating truly big
problems for
          physics, not to mention humanity as a whole.

          A paper on the second new experiment, by Daniela Mugnai,
          Ranfagni and Rocco Ruggeri of the Italian National Research
          described what appeared to be slightly faster-than-c
propagation of
          microwaves through ordinary air, and was published in the May
22 issue
          of Physical Review Letters.

          The kind of chamber in Dr. Wang's experiment is normally used
          amplify waves of laser light, not speed them up, said Aephraim
          Steinberg, a physicist at the University of Toronto. In the
          arrangement, one beam of light is shone on the chamber,
exciting the
          cesium atoms, and then a second beam passing thorugh the
          soaks up some of that energy and gets amplified when it passes

          But the amplification occurs only if the second beam is tuned
to a certain
          precise wavelength, Dr. Steinberg said. By cleverly choosing a
          different wavelength, Dr. Wang induced the cesium to speed up
a light
          pulse without distorting it in any way. "If you look at the
total pulse that
          comes out, it doesn't actually get amplified," Dr. Steinberg

          There is a further twist in the experiment, since only a
particularly strange
          type of wave can propagate through the cesium. Waves Light
          consisting of packets of waves, actually have two important
speeds: the
          speed of the individual peaks and troughs of the light waves
          and the speed of the pulse or packet into which they are
bunched. A
          pulse may contain billions or trillions of tiny peaks and
troughs. In air the
          two speeds are the same, but in the excited cesium they are
not only
          different, but the pulses and the waves of which they are
composed can
          travel in opposite directions, like a pocket of congestion on
a highway,
          which can propagate back from a toll booth as rush hour
begins, even as
          all the cars are still moving forward.

          These so-called backward modes are not new in themselves,
          been routinely measured in other media like plasmas, or
ionized gases.
          But in the cesium experiment, the outcome is particularly
strange because
          backward light waves can, in effect, borrow energy from the
          cesium atoms before giving it back a short time later. The
overall result is
          an outgoing wave exactly the same in shape and intensity as
the incoming
          wave; the outgoing wave just leaves early, before the peak of
          incoming wave even arrives.

          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
          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

          Someone who looked only at the beginning and end of the
          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."

          In Dr. Wang's experiment, the outgoing pulse had already
traveled about
          60 feet from the chamber before the incoming pulse had reached
          chamber's near side. That distance corresponds to 60
billionths of a
          second of light travel time. But it really wouldn't allow
anyone to send
          information faster than c, said Peter W. Milonni, a physicist
at Los
          Alamos National Laboratory. While the peak of the pulse does
          pushed forward by that amount, an early "nose" or faint
precursor of the
          pulse has probably given a hint to the cesium of the pulse to

          "The information is already there in the leading edge of the
pulse," Dr.
          Milonni said. "You can get the impression of sending
          superluminally even though you're not sending information."

          The cesium chamberhas reconstructed the entire pulse shape,
using only
          the shape of the precursor. So for most physicists, no
          principles have been smashed in the new work.

          Not all physicists agree that the question has been settled,
though. "This
          problem is still open," said Dr. Ranfagni of the Italian
group, which used
          an ingenious set of reflecting optics to create microwave
pulses that
          seemed to travel as much as 25% faster than c over short

          At least one physicist, Dr. Guenter Nimtz [[umlaut over u]] of
          University of Cologne, holds the opinion that a number of
          including those of the Italian group, have in fact sent
          superluminally. But not even Dr. Nimtz believes that this
trick would
          allow one to reach back in time. He says, in essence, that the
time it
          takes to read any incoming information would fritter away any
          advantage, making it impossible to signal back and change
events in the

          However those debates end, however, Dr. Steinberg said that
          closely related to Dr. Wang's might someday be used to speed
up signals
          that normally get slowed down by passing through all sorts of
          materials in circuits. A miniaturized version of Dr. Wang's
setup "is
          exactly the kind of system you'd want for that application,
Dr. Steinberg

          Sadly for those who would like to see a computer chip without
a speed
          limit, the trick would help the signals travel closer to the
speed of light,
          but not beyond it, he said.

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