[tt] NS: Michio Kaku: Impossible physics: Never say never

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Michio Kaku: Impossible physics: Never say never
http://www.newscientist.com/article.ns?id=mg19826501.600&print=true
8.4.5

Web special: 10 impossibilities that weren't

IMPOSSIBLE! Preposterous! These words are often thrown about when
people declare certain things to be scientifically ridiculous.
Aliens cannot reach the Earth in spaceships, they proclaim, because
the distance between stars is too great. Telepathy is impossible
since the brain does not emit or receive messages. And it's
impossible to instantaneously transport an object from A to B
because you cannot know the location and momentum of all its atoms -
teleportation would violate the Heisenberg uncertainty principle.

Yet if you carefully analyse these examples, you realise that they
are merely impossible today or in the near future. The real question
is, are they impossible with technologies that lie decades,
centuries or even millennia beyond ours? Perhaps these
"impossibilities" are merely very difficult engineering problems.
The late Arthur C. Clarke once said, "Any sufficiently advanced
technology is indistinguishable from magic." So a better question
would be: do these impossibilities violate the known laws of
physics?

History has shown that it is always dangerous to declare something
impossible. The celebrated Victorian physicist Lord Kelvin was known
not only for his pioneering work on thermodynamics, but also for
making a number of incorrect predictions. He said flatly that
"heavier-than-air" craft were impossible. He also thought X-rays
were a hoax, and that radio had no future. For good measure, he
declared that the Earth could be no older than a few million years.

Not to be outdone, Ernest Rutherford, who in 1911 discovered the
nucleus of the atom, was once asked if an atomic bomb could release
the energy stored in the nucleus. He quickly dismissed the idea.
Indeed, the road to progress is littered with erstwhile
impossibilities. Having seen so many of these become realities,
physicists today paraphrase T. H. White in The Once and Future King:
anything that is not forbidden is mandatory. Unless there is a law
of physics forbidding a technology, then it is not only possible, it
is sure to be built someday.

A more systematic approach to understanding the physics of the
impossible is to establish a hierarchy. I divide impossibilities
into three categories. Class I are those that might become possible
within a few decades to perhaps a century. Class II are those that
may take centuries, millennia or more to perfect. And Class III are
those that violate the known laws of physics, which I argue makes
them truly impossible.

What Class I impossibilities have in common is that they could be
achieved in the foreseeable future using the known laws of physics,
but may require sophisticated engineering. These include
invisibility, force fields, ray guns, psychokinesis, starships,
antimatter engines and even certain forms of teleportation and
telepathy.

For instance, I used to teach students in my optics class that
invisibility was impossible. For an object to become invisible,
light would have to wrap around it, like water flowing past a
boulder. Downstream the presence of the boulder has been totally
washed out. However, using Snell's law, which describes how uniform
materials refract or bend radiation, you can show that light would
have to travel faster than the speed of light in order to bend
around an object in that way. This would seem to be impossible.

However, two years ago physicists at Duke University in North
Carolina and Imperial College London showed that a "metamaterial"
can render an object inside it invisible to microwave radiation. By
placing tiny impurities within a material, they could force it to
bend microwaves in novel ways. And just last year two groups, from
the California Institute of Technology in Pasadena and the
University of Karlsruhe in Germany, succeeded in creating
metamaterials capable of bending red and green laser light in the
same manner. This is a significant breakthrough, since for the first
time we can bend visible light in a way that could eventually
produce invisibility devices.

Given the astonishing pace of scientific discovery, it is
conceivable that within a decade or two, physicists may be able to
render an object totally invisible, at least to a single colour of
light. Who knows, an invisibility cloak somewhat like Harry Potter's
could be possible within this century. This is just one example.

Another is telepathy, long considered the province of mystics,
cranks and magicians. Yet these days MRI machines are becoming so
sensitive that scientists at the University of Pennsylvania in
Philadelphia claim they can spot brain activity that indicates
someone is telling a lie. In the future, researchers may be able to
compile a "dictionary of thought" - a one-to-one correspondence
between brain signals and specific thoughts. Within a decade we
might be able to catalogue the thoughts behind a score of different
MRI patterns, for instance.

This mental information could then in principle be transmitted
between people. Neuroscientists at Brown University in Rhode Island
have implanted an array of electrodes directly into a paralysed
patient's brain, with the array wired up to a computer. The patient
has learned to move the cursor on a laptop screen just by thinking -
and can do it well enough to play simple video games and answer
email. As neural prostheses improve, stroke patients and others
afflicted by brain injuries may be able to communicate in ways that
were once inconceivable.

Likewise, the idea of teleportation was once considered impossible.
Yet today physicists regularly teleport single photons over
distances of 600 metres, and can also teleport whole caesium and
beryllium atoms. More precisely, they can teleport the quantum
information contained within a photon or atom onto a distant photon
or atom. Within a decade, the first molecule may be teleported in
this way, and within a few decades researchers could teleport more
complex organic molecules and perhaps even the first virus or strand
of DNA.

To achieve this, physicists exploit an exotic property called
quantum entanglement. If two particles are brought together in such
a way that their quantum wave functions vibrate in unison, then they
form a bond like an invisible umbilical cord that connects them even
if they are separated by vast distances. If you later disturb one
particle, then the information you impart onto it is transmitted
instantaneously to its partner - so the entangled partner forms a
ready-and-waiting template for whatever information is to be
teleported. Demonstrations of this phenomenon mean quantum
teleportation is in theory only a Class I impossibility.

Entanglement is a very delicate phenomenon, however. The two
particles have to be vibrating in precise unison, so the slightest
disturbance can break the ephemeral bond. This is the main reason
why it is hard to progress beyond a few atoms. In principle,
entangling large objects is just an engineering problem, but in
practice it is extremely difficult to get more than a handful of
atoms to stay in precise synchronisation. Teleporting a person made
of trillions of atoms may take several centuries to perfect - and
that takes us into the next class of impossibility.

Class II impossibilities are much more difficult. They may require
millennia or even millions of years to achieve, but crucially they
remain within the realm of possibility. What makes them so difficult
is that they generally require vast amounts of energy, and their
underlying physics is not totally understood. This class includes
time travel, faster-than-light travel via wormholes, and entering
parallel universes.

Stephen Hawking tried in the 1990s to prove that there must be a law
of physics preventing time travel, which he called the chronology
protection conjecture. Yet after years of hard work he failed, and
he now concedes that time travel is possible, though highly
impractical. A careful study of Einstein's equations of general
relativity shows that if you could assemble huge amounts of energy,
you could indeed open up a hole in space and time, perhaps
connecting the present to the past. Anyone brave enough to enter
this wormhole might find himself emerging before he left.

There are huge obstacles to building a time machine or wormhole,
though, not least that you'd need to assemble astronomical amounts
of energy, roughly equivalent to the mass of a black hole. In 1963,
physicist Roy Kerr was able to show that the singularity of a
spinning black hole might form a ring rather than a dot, and that
anyone falling through the ring might not be crushed to death, but
instead enter a parallel universe. Although astronomers have now
identified hundreds of spinning black holes in outer space, there is
a problem (beyond getting there in the first place): each
singularity is surrounded by an event horizon, so that you can't
return after passing through.

However, in 1988 physicist Kip Thorne found a solution of Einstein's
equations that was "traversable", corresponding to a wormhole that
in principle would let you go back and forth. A round trip through
the wormhole could be as straightforward as a ride on a plane, but
to open up such a wormhole you'd need the energy equivalent of a
stellar black hole's mass. What's more, keeping the wormhole open
and stable would require negative energy - an exotic phenomenon in
which quantum fluctuations render the energy density in a region of
space less than zero - equivalent to the mass of Jupiter. Physicists
have been able to create minuscule amounts of negative energy in the
lab, but this technology is only conceivable for a civilisation
significantly more advanced than ours.

That hasn't stopped physicists from proposing specific designs for
time machines. My favourite envisions a battery of atom smashers -
each about 10 light years long and capable of accelerating particles
at 200 billion electronvolts per metre - arranged in a sphere where
they all point inwards. These accelerators would fire converging
beams of particles at the centre of the sphere until that point
reaches something called the Planck energy, which is about 10^19
billion electronvolts. This is the energy at which space and time
become unstable and wormholes should appear.

All this is nothing compared with the granddaddy of them all: the
Class III impossibilities, those that genuinely violate the known
laws of physics. Either they are truly impossible, or we will have
to discover new laws of physics. I once made a list of seemingly
outlandish technologies found in science fiction, and realised to my
surprise that most were Class I or II. After careful study, I found
only two impossibilities that qualified as Class III: perpetual
motion machines, and precognition.

No-go ideas

The latter is defined as foretelling the future. This is problematic
because it violates causality, the fundamental ordering of cause and
effect. Precognition is actually a problem within time travel, but
physicists have devised ingenious ways to make time travel
consistent with causality; if you tinker with the past, for example,
perhaps you open up a parallel universe so there is still no
foretelling the future. But if true precognition were shown to exist
- say, a telephone line linking the present to the future - it would
represent a collapse of the foundations of physics.

As for perpetual motion, it has been the subject of a string of
hoaxes going as far back as the 8th century. Most are quite simple.
They usually involve a spinning wheel or chain of some sort. After
each cycle, a tiny amount of energy is produced apparently from
nowhere, and so the inventor claims that over many cycles he can
extract unlimited energy for free.

Perhaps the most celebrated perpetual motion machine was created in
1872 by John Keely, who swindled wealthy investors out of $5
million. It consisted of resonating tuning forks that he claimed
could extract energy from the "ether". Keely would regularly invite
investors to his house and dazzle them with his
hydro-pneumatic-pulsating-vacuo-engine, which whizzed about without
any apparent power source. He spent some time in jail for his
swindling, but died a wealthy man. After his death his house was
torn down, revealing an elaborate network of concealed tubes that
secretly supplied compressed air to his machines.

Even so, you might still be wondering: why don't perpetual motion
machines work? Why do we have the law of conservation of matter and
energy in the first place? If we knew the answer, then perhaps we
could find a clever way to evade it.

When I was a graduate student in physics, I learned the reason
behind this hallowed principle, which is something called Noether's
theorem. It states that whenever a system has a conservation law,
its origin lies in a "symmetry" of the system. For example, because
the laws of Newton and Einstein have a symmetry - they don't change
with time - they automatically possess a conservation law. The
fundamental laws appear to be immutable, no matter how long we wait,
and according to Noether's theorem this inevitably produces
conservation of energy.

I suddenly realised its significance: if you analyse the light
coming from galaxies billions of light years away, you find the very
same spectral lines of hydrogen that we find in our laboratories. In
other words, the laws of atomic physics have not changed for
billions of years, going right back to the big bang, and so energy
must have been conserved since the beginning of the universe. The
conservation of energy has been valid for billions of years, and its
violation by perpetual motion would signal a collapse in our known
laws of physics.

We now see the difference between Class III and the other types of
impossibilities. The essence is that Class I and II are compatible
with the two dominant theories of modern physics, quantum mechanics
and general relativity. So far, no one has found a single deviation
to either within its respective realm. And in both quantum mechanics
and general relativity, the fundamental laws remain the same over
time - they conserve matter and energy.

Might the fundamental laws of physics themselves be incomplete,
though? Perhaps. After all, relativity is thought to break down at
the instant of the big bang or at the centre of a black hole, and
quantum theory cannot explain gravity. At present, the leading
contender to combine quantum mechanics and relativity into a single
theory is superstring theory (which is what I do for a living), and
its laws too remain constant over time.

In considering what the future may hold, then, we should keep an
open mind to Class I and II impossibilities. What is unthinkable
today might not be forbidden in a few decades or centuries. Yet we
also have to draw the line somewhere and keep our feet firmly
planted in the known laws of physics. Ultimately they are the best
guide we've got.

Related Articles

2008: Does time travel start here?
http://www.newscientist.com/article.ns?id=mg19726421.700
09 February 2008

The replicator: create your own body double
http://www.newscientist.com/article.ns?id=mg18625031.800
11 June 2005

Invisibility cloaks: Now you see them...
http://www.newscientist.com/article.ns?id=mg19325911.900
16 February 2007

The Big Questions: Will we ever have a theory of everything?
http://www.newscientist.com/article.ns?id=mg19225780.074
16 November 2006

Weblinks

Michio Kaku's site
http://www.mkaku.org/

Stephen Hawking's site
http://www.hawking.org.uk/

Kip Thorne, California Institute of Technology
http://www.its.caltech.edu/~kip/

David Smith's metamaterials page, Duke University
http://www.ee.duke.edu/~drsmith/about_metamaterials.html


10 impossibilities conquered by science
http://www.newscientist.com/article.ns?id=dn13556&print=true
8.4.3

by Michael Marshall

What is truly impossible? To accompany Michio Kaku's article on the
physics of impossibility, we have rounded up 10 things that were
once thought scientifically impossible. Some were disproved
centuries ago but others have only recently begun to enter the realm
of possibility.

1. Analysing stars

In his 1842 book [13]The Positive Philosophy, the French philosopher
Auguste Comte wrote of the stars: "We can never learn their internal
constitution, nor, in regard to some of them, how heat is absorbed
by their atmosphere." In a similar vein, he said of the planets: "We
can never know anything of their chemical or mineralogical
structure; and, much less, that of organized beings living on their
surface."

Comte's argument was that the stars and planets are so far away as
to be beyond the limits of our sense of sight and geometry. He
reasoned that, while we could work out their distance, their motion
and their mass, nothing more could realistically be discerned. There
was certainly no way to chemically analyse them.

Ironically, the discovery that would prove Comte wrong had already
been made. In the early 19th century, William Hyde Wollaston and
Joseph von Fraunhofer independently discovered that the spectrum of
the Sun contained a great many dark lines.

By 1859 these had been shown to be atomic absorption lines. Each
chemical element present in the Sun could be identified by analysing
this pattern of lines, making it possible to discover just what a
star is made of.

2. Meteorites come from space

Astronomers look away now. Throughout the Renaissance and the early
development of modern science, astronomers refused to accept the
existence of meteorites. The idea that stones could fall from space
was regarded as superstitious and possibly heretical - surely God
would not have created such an untidy universe?

The [14]French Academy of Sciences famously stated that "rocks don't
fall from the sky". Reports of fireballs and stones crashing to the
ground were dismissed as hearsay and folklore, and the stones were
sometimes explained away as "thunderstones" the result of lightning
strikes.

It was not until 1794 that Ernst Chladni, a physicist known mostly
for his work on vibration and acoustics, published a book in which
he argued that [15]meteorites came from outer space. Chladni's work
was driven by a "fall of stones" in 1790 at Barbotan, France,
witnessed by three hundred people.

Chladni's book, On the Origin of the Pallas Iron and Others Similar
to it, and on Some Associated Natural Phenomena, earned him a great
deal of ridicule at the time. He was only vindicated in 1803, when
Jean-Baptiste Biot analysed another fall of stones at L'Aigle in
France, and found conclusive evidence that they had fallen from the
sky.

3. Heavier-than-air flight

The number of scientists and engineers who confidently stated that
heavier-than-air flight was impossible in the run-up to the Wright
brothers' flight is too large to count. Lord Kelvin is probably the
best-known. In 1895 he stated that "heavier-than-air flying machines
are impossible", only to be proved definitively wrong just eight
years later.

Even when Kelvin made his infamous statement, scientists and
engineers were closing rapidly on the goal of heavier-than-air
flight. People had been flying in balloons since the late eighteenth
century, and by the late 1800s these were controllable. Several
designs, such as Félix du Temple's Monoplane, had also taken to the
skies, if only briefly. So why the scepticism about heavier-than-air
flight?

The problem was set out in 1716 by the scientist and theologian
Emanuel Swedenborg in an article describing a design for a flying
machine. Swedenborg wrote: "It seems easier to talk of such a
machine than to put it into actuality, for it requires greater force
and less weight than exists in a human body."

Swedenborg's design, like so many, was based on a flapping-wing
mechanism. Two things had to happen before heavier-than-air flight
became possible. First, flapping wings had to be ditched and
replaced by a gliding mechanism. And secondly, engineers had to be
able to call on a better power supply the internal combustion
engine. Ironically, Nicolaus Otto had already patented this in 1877.

4. Space flight

>From atmospheric flight, to space flight. The idea that we might one
day send any object into space, let alone put men into orbit, was
long regarded as preposterous.

The scepticism was well-founded, since the correct technologies were
simply not available. To travel in space, a craft must reach escape
velocity for vehicles leaving Earth, this is 11.2 kilometres per
second. To put this figure into perspective, the sound barrier is a
mere 1,238 kilometres per hour, yet it was only broken in 1947.

Jules Verne proposed a giant cannon in his novel From the Earth to
the Moon. However, such a sudden burst of acceleration would
inevitably kill any passengers instantly, and calculations have
shown no cannon could be powerful enough to achieve escape velocity.

The problem was effectively cracked in the early 20th century by two
rocket researchers working independently Konstantin Tsiolkovsky and
Robert Goddard. Tsiolkovsky's work was ignored outside the USSR,
while Goddard withdrew from the public gaze after scathing criticism
of his ideas. Nonetheless, the first artificial satellite, Sputnik,
was eventually launched in 1957, and the first manned spaceflight
followed four years later. Neither Tsiolkovsky nor Goddard lived to
see it.

5. Harnessing nuclear energy

On 29 December 1934, Albert Einstein was quoted in the Pittsburgh
Post-Gazette as saying, "There is not the slightest indication that
[nuclear energy] will ever be obtainable. It would mean that the
atom would have to be shattered at will." This followed the
discovery that year by Enrico Fermi that if you bombard uranium with
neutrons, the uranium atoms split up into lighter elements,
releasing energy.

Einstein's scepticism was, however, overtaken by events. By 1939,
nuclear fission was better understood and researchers had realised
that a chain reaction one that, once started, would drive itself at
increasing rates could produce a huge explosion. In late 1942, such
a chain reaction was produced experimentally, and on August 6 1945
the first atomic bomb used aggressively exploded over Hiroshima.
Ironically, [16]Fleet Admiral William Leahy allegedly told President
Truman: "This is the biggest fool thing we've ever done the bomb
will never go off and I speak as an expert on explosives."

Then, in 1954, the USSR became the first country to supply some of
its electricity from nuclear power with its Obninsk nuclear power
plant.

6. Warm superconductors

This is a strange case: a phenomenon can be observed and measured,
but should not be happening. According to the best theories of
superconductivity, the phenomenon of superconductivity should not be
possible above 30 Kelvin. And yet some superconductors work
perfectly well at 77 K.

Superconductors materials that conduct electricity with no
resistance were first discovered in 1911. To see the effect, a
material normally has to be cooled to within a few degrees of
absolute zero.

Over the next 50 years, many superconducting materials were
discovered and studied, and in 1957 a complete theory describing
them was put forward by John Bardeen, Leon Cooper and John
Schrieffer. Known as "BCS theory", it neatly explained the behaviour
of standard superconductors.

The theory states that electrons within such materials move in
so-called Cooper pairs. If a pair is held together strongly enough,
it can withstand any impacts from the atoms of the material, and
thus experiences zero electrical resistance. However, the theory
suggested that this should only be true at extremely low
temperatures, when the atoms only vibrate slightly.

Then, in a [17]classic paper published in 1986, Johannes Georg
Bednorz and Karl Alexander Müller turned the field upside-down,
discovering a material capable of superconducting at up to 35 K.
Bednorz and Müller received the Nobel Prize for Physics the
following year and more high-temperature superconductors followed.
The [18]highest cutoff temperature yet observed (admittedly under
pressure) is 164 K. Yet, quite how this is all possible remains a
topic of intense research.

7. Black holes

People who think of black holes as a futuristic or modern idea may
be surprised to learn that the basic concept was first mooted in
1783, in a [19]letter to the Royal Society penned by the geologist
John Michell. He argued that if a star were massive enough, "a body
falling from an infinite height towards it would have acquired at
its surface greater velocity than that of light... all light emitted
from such a body would be made to return towards it by its own
proper gravity."

However, throughout the 19th century the idea was rejected as
outright ridiculous. This was because physicists thought of light as
a wave in the ether it was assumed to have no mass, and therefore to
be immune to gravity.

It was not until Einstein published his [20]theory of general
relativity in 1915 that this view had to be seriously revised. One
of the key predictions of Einstein's theory was that light rays
would indeed be deflected by gravity. Arthur Eddington's
measurements of star positions during a solar eclipse showed that
their light rays were deflected by the Sun's gravity though actually
the effect was too small for Eddington's instruments to reliably
observe, and it was not properly confirmed until later on.

But, once relativity was established, black holes became a serious
proposition and their properties were worked out in detail by
theoreticians such as Subrahmanyan Chandrasekhar. Astronomers then
began searching for them, and accumulated evidence that black holes
are common with one at the centre of many galaxies (including our
own) and the biggest ones being responsible for high-energy cosmic
rays.

Perhaps the debate has not been entirely settled, though. Some
controversial calculations, published in 2007, suggested that as
stars collapsed into black holes, they would release a great deal of
radiation, reducing their mass so that they do not form "true" black
holes after all.

8. Creating force fields

This classic of science fiction went from wild speculation to
verifiable fact in 1995 with the invention of the "plasma window".

Devised by Ady Hershcovitch from the Brookhaven National Laboratory,
the plasma window uses a magnetic field to fill a small region of
space with plasma or ionised gas. The devices, developed by
Hershcovitch and the company Acceleron, are used to reduce the
energy demands of electron beam welding.

The plasma window has most of the properties we associate with force
fields. It blocks matter well enough to act as a barrier between a
vacuum and the atmosphere. It also allows lasers and electron beams
to pass through unimpeded and will even glow blue, if you make the
plasma out of argon.

The only drawback is that it requires huge amounts of energy to
produce plasma windows of any size, so current examples are very
small. In theory, though, there is no reason they could not be made
much bigger.

9. Invisibility

Invisibility is another staple of fantasy fiction, appearing in
everything from Richard Wagner's opera Das Rheingold to H. G. Wells'
The Invisible Man, and of course Harry Potter.

There is nothing in the laws of physics to say invisibility is
impossible, and recent advances mean certain types of cloaking
device are already feasible.

The last few years have seen a rash of reports concerning
experimental invisibility cloaks, ever since a basic design for one
was produced in 2006. These devices rely on [21]metamaterials to
guide light around objects. The first of these only worked on
microscopic objects and with microwaves.

It was thought that modifying the design for visible light would
prove very challenging, but in fact it was done just one year later
- albeit only in two dimensions and on a micrometre scale. The
engineering challenges involved with building a practical
invisibility cloak remain formidable.

10. Teleportation

This is a word with a long and rather dubious history. It was coined
by the paranormalist writer Charles Fort in [22]his book Lo! and was
subsequently seized on by legions of science fiction writers; most
famously as the "transporter" in Star Trek.

Despite its fantastical origins, physicists have achieved a kind of
teleportation thanks to a bizarre quantum phenomenon called
entanglement. Particles that are entangled behave as if they are
linked together no matter how wide the distance between them. If,
for example, you change the "spin" of one entangled electron, the
spin of its twin will change as well.

Entangled particles can therefore be used to "teleport" information.
Performing the trick with anything larger than an atom was once
thought impossible, but in 2002 a theoretical way to entangle even
large molecules, providing they can be split into a quantum state
known as superposition, was described.

More recently, an alternative idea, dubbed "classical
teleportation", was proposed for making a beam of rubidium atoms
effectively disappear in one place and reappear elsewhere. This
method would not rely on entanglement, but transmitting all the
information about these atoms through a fibre optic cable so that

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Take me to the limits
http://www.newscientist.com/article.ns?id=mg15821386.000
98.6.14

Weblinks
Famous authoritative pronouncements
http://www.av8n.com/physics/ex-cathedra.htm

References

   13. http://socserv2.mcmaster.ca/~econ/ugcm/3ll3/comte/
   14. http://www.academie-sciences.fr/actualites/nouvelles_gb.htm
   15. http://www.meteorlab.com/METEORLAB2001dev/metics.htm
   16. http://www.williamdleahy.com/
   17. http://dx.doi.org/10.1007/BF01303701
   18. http://dx.doi.org/10.1103/PhysRevB.50.4260
   19. http://dx.doi.org/10.1098/rstl.1784.0008
   20. http://en.wikipedia.org/wiki/General_relativity
   21. http://en.wikipedia.org/wiki/Metamaterial
   22. http://www.resologist.net/lo102.htm
   23. http://www.newscientist.com/article.ns?id=mg15821386.000
   24. http://www.newscientist.com/article.ns?id=mg15821386.000
   25. http://www.newscientist.com/article.ns?id=mg19826501.600
   26. http://www.newscientist.com/article.ns?id=mg19826501.600
   27. http://www.av8n.com/physics/ex-cathedra.htm
   28. http://www.av8n.com/physics/ex-cathedra.htm
   29. http://www.newscientist.com/article.ns?id=dn13556

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