|Date:||5/19/01 12:13:38 PM Pacific Daylight Time|
Crossing fingers for the success of the experiment!
If your dad told you how to go faster than light, would you build a
machine to do it? Nick Appleyard and Bridget Appleby investigate
THE SPEED of light can't be exceeded. Everyone knows that. Yet Houshang
Ardavan of Cambridge University claims that there are sources of radio
waves out in space that move faster than light. A team of physicists at
Oxford, including Ardavan's son, has built a "superluminal" source based
on Ardavan's ideas. And any day now it could be switched on.
Many physicists think this idea is a complete waste of time. But if
they're wrong, and the Oxford experiment succeeds, Ardavan's patented
superluminal transmitters could soon turn up in your pocket. Their weird
radiation could transform technologies from medical scanners to mobile
Ardavan's work was inspired by the mysterious celestial objects known as
pulsars. Pulsars send out pulses of radio waves several times a second,
with timing so regular that they were at first thought to be alien
transmissions. Astronomers now believe that pulsars are the remnants of
massive stars that ended their lives in enormous supernova explosions.
Each supernova is thought to have left behind a ball of neutrons 1.4
times the mass of our Sun but only 20 kilometres across, its material so
dense that a teaspoonful would weigh three billion tonnes.
Although most astronomers agree on the basic nature of pulsars, the
radio pulses remain a bugbear. "More than 30 years after the discovery
of pulsars, we still don't know how the radio waves are produced," says
Janusz Gil of the J. Kepler Astronomical Center in Zielona Góra, Poland.
"Explaining pulsar radiation is one of the most difficult problems of
astrophysics." The regularity is thought to come from the fact that
pulsars spin, typically 10 to 20 times a second. Somehow they must send
out a beam of radio waves that sweeps past the Earth on each rotation.
But how? Most theories depend on the intense electric and magnetic
fields that are thought to surround a pulsar. The magnetic field can be
a hundred billion times the Earth's field -- strong enough to wrench a
spanner out of your hand from across the Atlantic. The general idea is
that the fields accelerate electrons near the pulsar, causing them to
emit radio waves. But to produce the required radio intensity, these
theories have to include some awkward assumptions (see "Tackling the
pulse", p 31).
Ardavan's theory is radically different. He says that the pulses we see
are "light booms"--shock waves made by a source moving faster than
light, rather like the sonic boom created by a supersonic plane when it
breaks the sound barrier. The idea of a light boom is not new. Because
light slows down inside materials such as water or glass, particles
moving in such a medium can travel at speeds faster than sluggish light.
These particles emit a flash of blue light called Cerenkov radiation.
Ardavan proposes that light booms could occur even in a vacuum, where
light travels at top speed. How can this be? According to Einstein's
theory of relativity, no material particle can move faster than light in
But a pattern can. For example, if a long line of drummers each hits a
drum in turn, the pattern of drumming can easily exceed light speed. Of
course, real drummers would have to be pretty skilled to hit their drum
each at the precise prearranged time.
Ardavan points out that faster-than-light patterns could be circling
around pulsars. A pulsar's magnetic field rotates along with the star.
As it does so, it induces a rotating pattern of electrical charges and
currents in the surrounding gas. This pattern rotates as if rigid, so
the farther out you go from the pulsar, the faster it sweeps by--just as
the spot illuminated by a lighthouse moves faster further out at sea.
Beyond about 5000 kilometres from the pulsar, the pattern will be
circling faster than the speed of light.
Vitaly Ginzburg and his co-workers at the Lebedev Physical Institute in
Moscow were the first to examine radiation from faster-than-light
patterns of charge. They predicted the existence of light booms, but
they didn't work out what would happen if the source moved on a curved
path--a question that requires fiendishly complicated maths. Ardavan
realised that much of the mathematics he needed had already been worked
out for supersonic systems, so he started by working on the theory of
supersonic helicopter blades, which mimic the whirling magnetic patterns
Adapting this work to his pulsar model, he calculated in 1994 that such
a rotating pattern would produce a shock wave of light. As each patch of
charge loops around, the waves it emits pile up in a complicated
fashion, crowding together especially strongly in a "cusp" of radiation
that follows a spiral path (see Diagram, p 30).
To explain the whirling beam that flashes radio waves at Earth, Ardavan
presumes that the overall charge pattern around a pulsar must be
lopsided. Perhaps a few closely clustered regions in the pattern act as
especially intense sources, and their cusps of radiation combine into
the radio beam.
This radiation has one strange unforeseen property. Radiation from any
ordinary source, be it lightbulbs or laser beams, spreads out and fades
rapidly as it travels. The intensity falls in proportion to the square
of the distance from the source. But in 1998, Ardavan published a paper
showing that radiation from a superluminal source should fade only in
proportion to the distance (Physical Review E, vol 58, p 6659). The
reason for this slower decay is that further from the source, the set of
waves forming the cusp overlap and get squashed together into a tighter
beam, so the intensity will no longer drop off as quickly.
Ardavan's ideas aren't popular, however. Among those who disagree
violently is Tony Hewish of Cambridge University--one of the original
discoverers of pulsars. The entire concept is wrong, he says. "Frankly,
I think the error is in equation one." He doesn't believe that a
collection of particles all moving slower than light can produce
superluminal shock waves, even if the charge pattern moves faster than
light. Hewish also points out that many common types of antenna and
waveguide already carry superluminal charge patterns, yet this slower
decay in brightness has never been seen.
Ardavan accepts this, but says an antenna would have to be curved to
emit his slow-decay waves. The charge patterns not only have to be
moving faster than light, they must be accelerating. Speeding up,
slowing down or moving around in a circle would do, but steady motion
will not produce the vital cusp.
Ardavan claims that there is already evidence to support his theory. In
1999, Shauna Sallmen and co-workers from the University of California at
Berkeley used a high-resolution technique to examine the pulsar at the
heart of the Crab Nebula. Instead of a single source, they saw three
separate points--a characteristic of superluminal sources. As Jean-Luc
Picard of the USS Enterprise has demonstrated, a starship that exceeds
the speed of light can overtake its own image and appear to be in more
than one place at a time. So the Crab pulsar seems to be performing the
Picard manoeuvre, appearing in three places at once. Ardavan was
Despite this, pulsar researchers have not embraced Ardavan's model. He
believes that this lack of acceptance might partly be due to a poor
understanding of the superluminal regime of electrodynamics, which he
says has taken him 20 years to comprehend. "Many of the unfamiliar
superluminal effects are at first sight counter-intuitive," he says.
Another problem is the formidable mathematics. To do his integrals
Ardavan uses an obscure technique that almost nobody else understands.
As pulsar theorist Don Melrose of the University of Sydney says: "The
combination of an unconventional idea and an unconventional approach
makes us all uncomfortable."
Melrose is sympathetic to the theory, but doesn't believe it actually
applies to pulsars. The rotating charge patterns, he thinks, would be
unstable. Other pulsar theorists object that Ardavan's theory doesn't
explain every detail of the observations.
This debate might have dragged on for decades, but two years ago a way
to test the theory appeared. Ardavan's son, Arzhang, became interested
in the problem after completing a doctorate in experimental physics at
Oxford. "My father's theory was dinner table conversation for a long
time," he says. He joined forces with John Singleton of the Clarendon
Laboratory, and together they now have £330,000 of research council
funding to build a table-top pulsar. The money had been earmarked for
developing "non-derivative" instruments--those based on original
principles. "This is wildly non-derivative," says Arzhang Ardavan with a
The core of their device is a curved rod of aluminium oxide covered with
electrodes. The voltage on each electrode will be oscillated at radio
frequency, with a slight time delay from one electrode to the next. The
idea is that this will mimic the line of drummers, to create a pattern
of waves that moves along the rod faster than light.
The hardware of their "polarisation synchrotron" is all in place, so now
Singleton and Arzhang Ardavan just have to get the delicate timing of
the electrodes right.
If it works, the weird radiation produced will be tremendously useful.
The device could be tuned to emit radiation over a very wide range of
the electromagnetic spectrum, including previously inaccessible
Terahertz waves penetrate the skin, but cause less tissue damage than
X-rays, so they could be used to diagnose skin and breast cancers, as
well as rotten teeth, with little health risk. Mobile phones using
terahertz waves would have access to a bandwidth thousands of times
greater than today's, making data-hungry applications like video
streaming a breeze. And a terahertz source could also be used as a
computer clock, allowing elements to switch far faster than in today's
Houshang Ardavan predicts that the radiation from this table-top pulsar
will fade more slowly than that from any other source. This would be
very useful for long-distance communications: space probes could send
information back to Earth using small, low-power superluminal
transmitters. Mobile phones could beam directly to a satellite without
needing a ground-based relay station, so you could use them anywhere on
Earth. Strangest of all would be a new means of transmitting secure
communications. With the right antenna, you could send out a pulse that
only assembles itself in one place, where the waves interfere
constructively--and in theory you could modulate this pulse to transmit
a signal. No one outside the target area would be able to intercept it.
Not surprisingly, Hewish's profound scepticism extends to the Oxford
project. "I think it's a great pity they're wasting their time on this."
Other astronomers take a slightly different view. "The physics is right:
there's nothing wrong with it," says Melrose. "I just don't believe that
this mechanism can be set up and sustained in a pulsar." In that case,
the new transmitter could still work--even if its inspiration proved to
"This is the most exciting experiment that I have worked on," says
Arzhang Ardavan. "Whatever happens, it will open up research in a whole
area of physics that people just haven't really considered before."
Singleton says: "I see no reason why it shouldn't work. Let's suck it
If the equipment does do something interesting when the switch is
thrown, tighten your seat belts. Twenty-first century technology is
about to lurch through the light barrier.
"Imagination is more important than knowledge."
^(º¿º)^ -UB- ^(º¿º)^