Fun_People Archive
22 Jun
FTL - Mozart Faster Than Light?

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From: Peter Langston <psl>
Date: Thu, 22 Jun 100 14:03:30 -0700
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Subject: FTL - Mozart Faster Than Light?

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From: Science News June 10, 2000, Vol 157, No.24, p.375

    Five years ago, a wave of discontent swept away the 55-mile-per-hour
U.S. speed limit.  Nowadays, some physicists are taking a hard look at the
670-million miles-per-hour speed limit of light in a vacuum, or C.
    Albert Einstein posted this limit in his 1905 theory of special
relativity.  Although popular lore and some physics textbooks still contend
that nothing races faster than C, experiments going back decades have
repeatedly shown that light can beat that speed under certain conditions.
    A few scientists argue that those experiments hint that Einstein was
wrong.  Two new experiments reveal dramatic additional evidence of
superluminal velocity but make no clear case for repealing Einstein's law,
scientists say.
    In one study, conducted in Italy, scientists propagated superluminal
microwaves through air by bouncing them off a mirror.  In the other, led
by a New Jersey researcher, a laser pulse approaching a gas-filled cell's
entry window materialized at the cell's exit glass before even reaching
the cell.
    Although superluminal phenomena might someday help speed up computers
- an avenue being explored by Raymond Y Chiao of the University of
California, Berkeley - the main excitement around these experiments stems
from basic physics implications.
    At stake is the idea that a cause must precede an effect.  If
experimenters found that information can go somewhere faster than C, "you
would get into nonsensical types of predictions, like going back in time
and shooting your grandmother," explains Peter W. Milonni of Los Alamos
(N.M.) National Laboratory.
    Gunter Nimtz of the University of Cologne in Germany contends that
information can indeed travel faster than C, casting doubts on both
causality and special relativity. In 1995, for example, his research team
encoded Mozart's 40th symphony in a microwave beam traveling at 4.7 times
C to a receiver.
    However, Aephraim M. Steinberg of the University of Toronto argues that
aside from Nimtz and a few other "vocal dissenters," mainstream physicists
agree that such experiments "do not support any idea of causality
violation."  One challenge, however, is to exactly define information, or
a signal.
    Experiments dating back to the early 1990s by Nimtz, Steinberg, Chiao,
and others have shown superluminal tunneling of optical photons through
mirrors (SN: 7/2/94, p.6) and of microwaves through so-called forbidden
zones of waveguides.
    The Italian scientists, led by Anedio Ranfagni of the Italian National
Research Council in Florence, devised their experiment so that reflected
microwaves in open air overlap and interfere as the waves speed away from
the mirror.  Constructive interference creates a moving puIse along the
axis of the apparatus whose speed varies according to the configuration of
the experiment.  The researchers report in the May 22 PHYSICAL REVIEW
LETTERS that within 1.4 meters of the mirror, they clocked such pulses at
up to 125 percent of C.  Beyond that distance, the effect dies out.
    Because electromagnetic waves radiate through air much as they do in
a vacuum, Chiao says, the "spectacular work" by the Italians
demonstrates that even in a vacuum, light could outpace C.
    In the laser experiment by Lijun Wang of NEC Research Institute in
Princeton, N.J., and his colleagues, the superluminal pulse, which was
preceded by a "pump" pulse to excite the amplifier, has a negative velocity.
That means that it "arrives at a distant point 'earlier' than it even
arrives at the input," explains Steinberg, who is acquainted with the
unpublished study but is not a coauthor.
    This isn't magic, he says. Rather, amplifiers, like the cell in the
experiment, respond to certain frequencies by building a replica of the
incoming pulse at the output.  In this case, the time a pulse with speed
C would take to cross the cell, multiplied by 300, is the head start the
outgoing pulse gains over the incoming one.
    What's more, any rounded pulse contains a central peak and tapering
wings extending far out behind and ahead.  The wings contain all the
information needed to reconstruct the peak, so as soon as the forward wing
of the incoming laser pulse arrives, the cell spits out a fullscale version
of the peak.
    Although Wang declined to discuss the study, which was submitted to
NATURE, some of its results were described May 30 in The New York Times.
-P. Weiss
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