Not Quite Val.  I deal with SOME of your physics errors and misconceptions
here at the end of the article, and then comment in another post on some of
your other, possibly incorrect, and politicized assertions.

R. Ruffini
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CROSSING THE QUANTUM FRONTIER

There is a mysterious boundary between the familiar predictability of
ordinary objects and the spooky uncertainties of the quantum world. Now
physicists are on the verge of discovering what happens there, says Mark
Buchanan

THE QUANTUM WORLD IS FAMOUS for its weirdness: its particles live in an
eerie world of uncertainties and ghostly multiple existences. We, on the
other hand, are surrounded by robust and solid certainty. It might be handy
to be in two places at once, but we'll never manage it. Although this
separation of the microscopic and the everyday might seem perfectly natural,
in fact it's anything but. According to quantum theory, quantum coexistence
is infectious: it should percolate up from the atomic world to ours, and
afflict us all. So why doesn't it?

This question has baffled some of the greatest minds in physics:
Schroedinger, Einstein, Dirac, and Feynman all failed to make sense of it.
But now, some 70 years after quantum theory first upset the apple cart,
salvation may finally be at hand. In the past few years, some daring
physicists have invented an ingenious new twist to the theory that could
finally unite the two worlds.

Erwin Schroedinger, one of the theory's founders, was the first to point out
that quantum weirdness should invade the classical world. He illustrated the
point with a famous thought experiment, which arranges a direct link from
the quantum world to ours. It works like this. In a box sits a radioactive
nucleus, a gun and a cat. Because it is radioactive, the nucleus can decay
and emit a neutron. Things are arranged so the neutron will trigger the gun
to shoot the cat.

If the nucleus remains whole, the cat lives, and if it decays, the cat dies.
But being a quantum particle, the nucleus doesn't have to choose between its
two possible states. Instead, it develops gradually into a strange
combination of both -- called a "superposition". Because of the link, the
split existence of the nucleus infects the cat as well. So if the nucleus
stays in its ghostly superposition of states, the cat stays in a ghastly
coexistence between life and death.

This conclusion follows unavoidably from the theory. But it seems like pure
nonsense. Cats are either alive or dead -- there is no in-between. Isn't
this just proof that something is dreadfully wrong with the theory?
Schroedinger thought so, and so did Einstein, who quipped that "if quantum
physics is correct, then the world is crazy". But neither could work out how
to fix it. Meanwhile, it was becoming increasingly obvious in the 1930s that
quantum theory worked very well for atoms and molecules. So physicists
devised an artificial solution. They just tacked an extra rule onto the
theory to forbid superpositions in big objects.

This extra rule -- known as the "measurement postulate" -- says that the
multiple existences of any object will collapse back to a single existence
whenever the object interacts with a "classical measuring device". That
could be all sorts of things -- a photographic plate, the eye of a human
being, or any other big object. In essence, the measurement postulate says
that big things don't get into superpositions because superpositions
collapse whenever they encounter big things. It's a policeman, patrolling
the border between classical and quantum worlds, and keeping multiple
existences down where they belong.

This artifice is effective for most practical purposes, but it still leaves
a mighty split between the quantum and classical worlds. The postulate
clearly says that there are some things, such as electrons and protons, that
act according to quantum rules, and others, such as photographic plates and
experimenters, that follow classical (non-quantum) rules. There are two
separate domains with their own distinct laws of physics. So much for a
unified theory of the world.

In their desperation to get rid of the ugly split, physicists have invented
countless schemes designed to show that the extra measurement postulate
arises somehow out of the combined action of the more natural rules of
quantum theory. But it simply cannot. The ordinary quantum rules preserve
multiple existences, whereas the measurement postulate destroys them, so
trying to wring one from the other is hopeless. John Bell, the world's
foremost quantum expert until his death in 1990, likened the effort to a
snake trying to swallow itself by the tail. "It can be done up to a point,"
he said. "But it becomes embarrassing for the spectators even before it
becomes uncomfortable for the snake."

Radical trio

So what is to be done? If quantum theory can't make sense of the single
existences of ordinary objects, it clearly needs some help. But the problem
is so staggeringly difficult that for many years only a few physicists even
tried to solve it. Then in 1986, three Italian physicists had a brilliant
idea. Aware of the early concerns of Einstein and Schroedinger, Gian-Carlo
Ghirardi of the University of Trieste, Alberto Rimini of the University of
Pavia, and Tullio Weber, also of Trieste, reckoned that the measurement
postulate disguised a deeper problem with the quantum rules themselves.
Change these, they thought, and perhaps you can drop the measurement rule.

In quantum theory, a "particle" does not sit in just one place, but occupies
many places all at once. Its true position is defined by a fuzzy blob called
a "wave function", which sets out the probability of finding the particle in
various locations. With time, the wave function of any particle spreads out,
bleeding into an expanding volume of space, as the particle's multiple
existences proliferate.

Ghirardi, Rimini and Weber proposed a subtle change in the quantum rules
that determine how wavefunctions evolve. Suppose, they said, wave functions
usually spread out according to normal quantum rules, but very rarely --
once every 100 million years or so -- the wavefunction of a single particle
collapses and becomes localized to a tiny region. This change scarcely
affects single particles, but has a huge effect on big things.

A cat or any other object of similar size contains some 10^27 particles. And
even though the wave function of any one is likely to take 100 million years
to collapse, there are so many particles that it is overwhelmingly likely
that the wave function of at least one particle will collapse within just
10^(-12) seconds. What's more, because the particles in an object interact
with one another, their wavefunctions are entangled. The normal quantum
rules then demand that the collapse in one particle instantaneously triggers
a collapse in all the others. The collapse of one particle's wave function
drags the whole lot into a definite state.

So in the scheme of Ghirardi, Rimini and Weber, electrons and protons act as
they should, and remain in superpositions for long times, but weird
living-dead cats are -- within a mere trillionth of a second -- either
spared or put out of their misery. All this follows naturally from the
theory, without any extra rules slapped on. There is no need to divide the
world into separate sets of laws.

This is an impressive achievement. And yet, the GRW theory has some big
problems of its own. After all, it doesn't begin to explain what would make
a wave function collapse, nor why it should happen only every 100 million
years. Also, according to Ian Percival, a physicist at Queen Mary and
Westfield College in London, the idea flies in the face of the way nature
usually works. He points out that in virtually all processes in the physical
world, changes over longer time intervals come about by the accumulation of
changes over shorter intervals. But in the GRW scheme, the interruptions on
long times that lead to collapse don't arise naturally from any processes
over shorter times. So it's difficult to imagine what might cause them.

Still unpalatable

This makes the GRW scheme almost as unpalatable as the ordinary quantum
theory with its bolted-on measurement rule. But in the past few years, some
new ideas have emerged that show how these problems might be solved. Most
notably, Percival, along with Nicholas Gisin of the University of Geneva,
has developed "quantum state diffusion theory", which stands the GRW picture
on its head.

Percival's and Gisin's idea was born of an analogy with an old problem in
physics -- Brownian motion. If you peer through a microscope at a dust
particle floating in water, you'll see that it bounces around erratically,
rather like a ball in a pinball machine. This "Brownian motion" is all down
to molecules. What happens is that in a liquid, the molecules move about
violently, zinging this way and that. A speck of dust endures a constant
barrage of such molecules, and the knocks it receives at their hands cause
its erratic jitter.

A dust particle in the air does much the same thing, but in between
molecular collisions, gravity relentlessly drags it down. Over very short
periods of time, the irregular, "noisy" part of this motion is most evident
as the dust particle flits to and fro. But over long times, the many
irregular motions add up, and out of the erratic jitter emerges the
particle's downward drifting motion.

What does this have to do with quantum theory? Percival and Gisin see the
natural and continuous spreading motion of a quantum particle's wave
function as a kind of drift, albeit of a more abstract kind. In normal
quantum theory, this drift is all there is. But in the GRW scheme, the wave
function's continuous drift (spreading) is interrupted every 100 million
years or so by a sudden, random event that drives it to collapse again to a
small volume. These random hits are rather like the molecular collisions of
Brownian motion, but the GRW picture doesn't quite fit the analogy. In the
GRW model, random collapse events tend to be separated by long periods of
time, during which a great deal of drift occurs. But the erratic events in
Brownian motion happen very frequently, and drift emerges as these rapid
events accumulate.

To develop a more natural theory, Gisin and Percival suggest that the random
fluctuations happen over very short periods, so that the state of a quantum
system follows a sort of Brownian motion. Over very short periods, the
irregular part of the motion is most important, and the wave function
fluctuates haphazardly. But over longer periods, the fluctuations add up to
give a steady development, and the wave function spreads as expected from
normal quantum theory.

But Percival and Gisin also include another element in their equations which
spell the end for multiple existences. This property of the equations, known
as "nonlinearity", arms the quantum world against itself. In effect, the
nonlinearities force the different partial existences of an object to
struggle against one another for supremacy, until all but one have been
eliminated, and the wavefunction has collapsed.

Just as in the GRW theory, collapse happens very slowly for single
particles, but very quickly for big ones. It works in much the same way. On
average, the struggle between the partial existences of any single particle
takes a very long time. But because of the random fluctuations it can
sometimes -- rarely -- happen quickly. Given the huge number of particles in
an ordinary object, it is overwhelmingly likely that at least one of them
will have collapsed back to a single existence in a tiny fraction of a
second. This collapse drags the entire collection of particles with it, so
the whole object reverts to a single existence.

Field in flux

This theory certainly seems to do the trick. But what could be causing the
fluctuations? One intriguing hypothesis is that they reflect irreducible
fluctuations in the very fabric of space-time itself. Tentative attempts by
physicists to build a quantum version of Einstein's general relativity --
which views gravity as curvature in the geometry of space-time -- suggest
that the Universe's gravitational field should fluctuate rapidly over
distances and times of about 10^(-35) metres and 10^(-44) seconds. So it may
be that these very fluctuations are popping up in Percival and Gisin's
theory. If so, it would seem that tangible effects of quantum gravity are
all around us, prohibiting multiple existences in big objects and keeping
Schroedinger's cat in one piece.

Even more remarkably, Percival and Gisin believe that it may soon be
possible to detect these fluctuations in the laboratory. Not directly, to be
sure. But they should have measurable effects on delicate interference
experiments.

Imagine a beam of particles split into partial existences which are sent
along different paths (see Diagram). According to quantum theory, each
particle is like a clock that oscillates with a characteristic frequency. So
the number of cycles it goes through by the time it gets to the screen
depends on how long it takes to get there. When they arrive, the partial
existences interfere with one another, forming a pattern that depends on
small differences in the number of cycles each clock has gone through.

But space-time fluctuations along the paths could disturb these
relationships -- because the fluctuations should make the clocks speed up or
slow down erratically as they travel. So the clock settings of the two
partial existences at the screen will vary randomly and the expected pattern
will be destroyed.

In 1992, Mark Kasevich and Steven Chu of Stanford University directed two
beams of sodium atoms along different paths some 15 centimeters long, and
found the pattern expected from normal quantum theory. So the fluctuations
-- if present -- didn't have noticeable effects. These experiments would be
sensitive enough to detect the fluctuations if they take place in around
10^(-44) seconds.

But the fluctuations may well be more rapid yet. One way to improve the
sensitivity of the experiments would be to allow the beams of atoms to
travel over longer distances before they interfere with each other. This is
trickier, because external noise would be harder to eliminate. But it would
give the effects of the fluctuations more time to accumulate, and should
provide a more sensitive probe within the next few years.

Contd.


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