From: Brian Atkins (brian@posthuman.com)
Date: Tue May 30 2000 - 21:33:46 MDT
Actually it was more about light than microwaves.. full text below.
"Ross A. Finlayson" wrote:
>
> Damien Broderick wrote:
>
> > At 02:29 PM 30/05/00 -0400, Brian Atkins <brian@posthuman.com>
> > wrote:
> >
> > >http://www.nytimes.com/library/national/science/053000sci-physics-light.html
> >
> > This is not accessible to anyone outside the States - that is, we can't
> > register.
> >
> > So what's the story about?
> >
> > Damien
>
> They got microwaves to fly faster than c. Purportedly the microwaves arrive
> prior to when they are sent. The gist was that they supposedly could not affect
> the prior time.
>
> Within the past years, IBM has shown matter transportation.
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 point.
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 superluminal
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
professor of
physics at the University of California in Berkeley, who, like a
number of
physicists in the close-knit community of optics research, is
knowledgeable
about Dr. Wang's work.
Dr. Chiao, whose own research laid some of the groundwork for the
experiment, added that "there's been a lot of controversy" over
whether the
finding means that actual information--like the news of an impending
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 under
review,
Dr. Wang said: "Our light pulses can indeed be made to travel 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, Anedio
Ranfagni and Rocco Ruggeri of the Italian National Research Council,
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 to
amplify
waves of laser light, not speed them up, said Aephraim M. Steinberg, a
physicist at the University of Toronto. In the usual arrangement, one
beam
of light is shone on the chamber, exciting the cesium atoms, and then
a
second beam passing thorugh the chamber soaks up some of that energy
and gets amplified when it passes through them.
But the amplification occurs only if the second beam is tuned to a
certain
precise wavelength, Dr. Steinberg said. By cleverly choosing a
slightly
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 said.
There is a further twist in the experiment, since only a particularly
strange
type of wave can propagate through the cesium. Waves Light signals,
consisting of packets of waves, actually have two important speeds:
the
speed of the individual peaks and troughs of the light waves
themselves,
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, having 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 excited 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 the 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 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."
In Dr. Wang's experiment, the outgoing pulse had already traveled
about
60 feet from the chamber before the incoming pulse had reached the
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 get 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 come.
"The information is already there in the leading edge of the pulse,"
Dr.
Milonni said. "You can get the impression of sending information
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 fundamental
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 distances.
At least one physicist, Dr. Guenter Nimtz [[umlaut over u]] of the
University of Cologne, holds the opinion that a number of experiments,
including those of the Italian group, have in fact sent information
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 temporal
advantage,
making it impossible to signal back and change events in the past.
However those debates end, however, Dr. Steinberg said that techniques
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 ordinary
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
said.
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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