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New Atom-Smasher Could Fill Gaps in Scientific Knowledge - or Open
a Black Hole
By John Johnson Jr.
The Los Angeles Times
Sunday 13 April 2008
Europe's enormous $8-billion particle accelerator,
to be activated as early as this summer, is generating both excitement and fear.
Geneva - Michelangelo L. Mangano, a respected particle physicist who helped
discover the top quark in 1995, now spends most days trying to convince people
that his new machine won't destroy the world.
"If it were just crackpots, we could wave them away," the physicist
said in an interview at the European Organization for Nuclear Research, known
by its French acronym, CERN. "But some are real physicists."
What the critics are in such a lather about is the $8-billion Large Hadron
Collider, a massive assemblage of iron, steel and superconducting wire 300 feet
underground in a 17-mile-long circular tunnel on the Franco-Swiss border.
The most complex piece of scientific equipment ever built, the collider will
send particles crashing into each other at just a wink shy of the speed of light,
generating energies more powerful than the sun.
Scientists like Mangano believe that this instrument, when it begins operating
as early as this summer, will peer into a looking-glass world that could contain
entrances to extra dimensions and super-massive partners of the familiar particles
that make up our world. One creature that must be hiding there, the scientists
say, is the Higgs particle, one of the most exotic undiscovered objects since
the yeti.
Critics think the collider could also spawn a black hole that will swallow
Earth.
That could be just an appetizer. Once the collider got going, according to
the doomsday scenario, it could gobble up distant stars like a child popping
Skittles.
Mangano, who is part of the CERN group studying the safety of the collider,
doesn't deny the scant possibility that the collider could yield a mini-black
hole.
By smashing protons and lead ions together at energies reaching 14 trillion
electron volts, the Large Hadron Collider will dwarf the world's other atom-smashers,
including the Fermi National Accelerator Laboratory's mighty Tevatron in Batavia,
Ill.
But that energy, Mangano hastened to add, would be concentrated in a space
thinner than a human hair. Any black hole would be so tiny that it wouldn't
be able to get its teeth around a bit of local chevre cheese, let alone the
world.
Still, if a black hole were produced at all, "that would be an extremely
spectacular result," he said, a half-smile creeping across his face.
Particle Physics
Deep in a dim cavern, UCLA physicist Bob Cousins scrambled onto a catwalk straddling
the six-story detector known as the Compact Muon Solenoid, then darted up two
flights of stairs to another catwalk, where the guts of the machine materialized
out of the half-light.
It looked a little like the inside of a computer suffering from a severe case
of gigantism. Plates, shields and pipes jutted everywhere. Thick knots of cable
extended from the side like mounds of heavy rope on an 18th century whaling
ship.
"This detector was assembled at the surface and lowered in 15 pieces,"
Cousins said, pointing to a wide opening above the detector that reached to
the European sky high above.
The heaviest piece weighed 4 million pounds. It took 10 hours to lower the
middle section. At the center of this section is a bulbous extension that makes
the behemoth look like the world's biggest television picture tube. This single
piece of the collider contains more iron than the Eiffel Tower.
It was all built to probe a beam of particles thinner than a blade of grass.
Decades ago, scientists figured out that atomic nuclei were made up of smaller
things than protons and neutrons.
To find those pieces, 20th century physicists came up with an idea that would
appeal to most 9-year-old boys with a new toy: "Let's smash it and see
what happens."
Early colliders, like the 9-inch cyclotron created at UC Berkeley in 1931,
sent particles down a circular drag strip and crashed them into a target to
see what flew out.
From there, particle physics exploded. Larger and more sophisticated devices
kept packing more energy into the colliding particles, allowing scientists to
peer deeper into the guts of the atom.
Protons and neutrons, they found, were made up of even smaller particles, dubbed
quarks, which were bound together by another set of particles, called gluons.
Gluons were part of a larger family, bosons, each of which carries some form
of force. Photons, which make up light, for example, carry the electromagnetic
force.
They found a bestiary of particles - pions, kaons, deltas and other exotically
named objects - that existed beyond an atom's nucleus.
Altogether, scientists found dozens of species of elementary particles, some
composed of pieces so tiny that they make an atom look like a sumo wrestler,
or a mountain. If a quark measured an inch, an atom would stretch at least 1,000
miles, about the distance from Los Angeles to Denver.
These discoveries enabled physicists to devise a compelling picture of the
universe at the subatomic level. Known as the Standard Model, it is considered
the most successful scientific theory in history.
It has been able to explain an array of processes through its description of
the subatomic world and the dynamics of the four essential forces of the universe:
gravity, electromagnetism, the weak force governing radioactive decay, and the
strong nuclear force, which binds protons and neutrons together in an atom's
nucleus.
But there are problems. First, the Standard Model can't explain why the universe
is composed of matter. According to theory, equal amounts of matter and antimatter
would have been created in the Big Bang, which created the universe. As soon
as they met, they should have annihilated each other, releasing photons of light.
"You should end up with a universe with only light," said Tatsuya
Nakada, who directs another of the four major particle detectors at CERN.
The Standard Model also fails to explain why particles have mass.
"In all our equations, the most fundamental particles that we know matter
is made of come up massless," said Pauline Gagnon, an Indiana University
physicist who works on a detector known as ATLAS. "We know that's a flaw
in the Standard Model."
The answers, scientists believe, lie in reactions with the extreme energies
that occurred during the first moments after the Big Bang. To reach those energies,
they have to push particles as close to the speed of light as possible.
The CERN collider uses a powerful electromagnetic field to accelerate particles.
"Think of a swing," said Sandor Feher, a fast-talking Hungarian-born
physicist, as he strode through a section of the long collider tunnel. "Each
time the beam comes around, the field pushes it a little faster."
At the peak, the hydrogen protons in the new collider will reach 99.9999991%
of the speed of light. Each packet of protons will complete 11,245 laps around
the collider every second and carry as much power as a speeding train.
The collider will consume as much energy as all the households in Geneva, running
up an annual electric bill of $30 million.
To guide the proton beams through the twin tubes of the collider, 9,600 magnets
will continually tune the positively charged protons as they speed around the
collider. The superconducting magnets are cooled with liquid helium to minus
456.25 degrees, a whisker above absolute zero.
Whatever objects spring into being in the collider won't last long. They will
be relatively big and thus inherently unstable and will quickly decay into more-familiar
particles.
Some of these weird objects may travel as much as a millimeter or two before
decaying, while others will travel less than the diameter of a proton before
vanishing in a shower of quarks, gluons, electrons or neutrinos.
Because the detectors will produce millions of collisions every second, scientists
will rely on huge clusters of computers to analyze the results. The computers
will discard almost all the collisions, preserving only the most unusual for
deeper analysis by humans.
Physicists aren't working completely in the dark. Extra dimensions, for example,
could show themselves by the unusual paths the decaying particles take as they
shoot off into the various layers of the detectors.
If all goes as planned, scientists say, the new collider is likely to become
one of the greatest engines of discovery in history, far outstripping the Apollo
moon missions and even Charles Darwin's monumental voyage aboard the Beagle.
"This is the elevator that will take us to the next floor" of discovery,
Mangano said.
Explaining Mass
The first big mystery to fall, theorists expect, will be the explanation for
mass.
The theory is most often attributed to Scottish physicist Peter Higgs, who
proposed about 40 years ago that the vacuum between the stars is not empty but
made of a fabric that extends infinitely in all directions.
This fabric, which Mangano compared to the ether that the Victorians believed
filled outer space, has come to be known as the Higgs field.
"There is something in the vacuum," Mangano said. "As a particle
moves, it interacts with the vacuum and acquires mass." Some physicists
compare this to a person walking on a dirt path after a rainstorm. As he walks,
his boots get caked with mud.
If the Higgs field is real, physicists say, it should have a fundamental particle
associated with it. Scientists have named the hypothetical particle the Higgs
boson.
Fermilab's Tevatron spent years trying to find it. The Large Electron-Positron
Collider at CERN saw tantalizing hints of the Higgs particle before it was shut
down in 2000 for construction of the new collider.
Physicists are confident of the Higgs boson's existence but think that it is
just too massive to be produced in smaller colliders.
But how could a collision of tiny particles like protons produce a massive
particle like the Higgs?
In our macro-world, crashing things together, like cars, makes big things into
smaller things, like broken headlights and fenders. But it's different in the
subatomic world, where crashing two Priuses together can produce a 10-wheeler.
"Remember," Gagnon said, "according to Einstein, mass is congealed
energy." In other words, if you create enough energy in one place, it can
remake itself into a chunk of mass.
Gagnon compared the particles that have been created in other colliders to
rubber ducks. "We've made millions of duckies," Gagnon said. "Now
we want to make an elephant."
Because the new collider will be seven times as powerful as the Tevatron, if
the Higgs boson exists, the CERN collider should find it.
"If we don't find the Higgs, the theorists have a lot of explaining to
do," said UCLA postdoctoral student Greg Rakness over lunch in the CERN
cafeteria, where one can hear conversations in a dozen languages.
The huge burst of energy in particle collisions becomes a kind of time machine,
transporting scientists back to the first microseconds after the Big Bang.
The universe was only about 200 million miles wide, consisting of a viscous
cloud of quarks and gluons floating in a searing plasma. As the universe expanded
and cooled, the quarks combined to make protons and neutrons. The gluons held
them together to form the nuclei of atoms.
To re-create this plasma, one of the collider's detectors, known as ALICE,
will accelerate heavy lead ions. One of the heaviest of all elements, each lead
atom contains 82 protons and 125 neutrons.
By pounding these sacks of protons and neutrons together, the scientists hope
to free the quarks and gluons from their embrace into a free-floating quark-gluon
plasma.
With this re-creation of the early moments of the universe, scientists may
also be able to delve into the unexplained imbalance between matter and antimatter.
So far, experiments have not been able to explain why there's so much matter
in the universe and no antimatter, beyond what is created in colliders.
According to experiments, there should be 1020 (100 billion billion) more photons
of light than protons of matter in the universe. In fact, Nakada said, the number
is closer to 1010. That's a huge amount of unexplained matter in the form of
galaxies, stars, planets and theoretical physicists.
A detector called the LHCb will try to unravel this mystery by making very
precise measurements of a certain kind of quark that is created in particle
collisions, the b meson, and its opposite, the anti-b meson.
Black Holes
Then there's the matter of black holes.
Harvey Newman, a Caltech physicist who was one of the discoverers of the gluon
and is leader of the U.S. contingent on the Compact Muon Solenoid experiment,
said the collider could theoretically produce a mini-black hole by packing a
tremendous amount of energy into a tiny space.
But he said the black hole would pose no threat because it would last only
10-27 seconds before decaying - hardly enough time to start gobbling up the
French countryside.
Critics are not convinced. Just last month, Walter L. Wagner and Luis Sancho
filed suit in U.S. District Court in Honolulu to block the start-up of the new
collider until CERN produces a comprehensive safety report.
Speaking from Hawaii, Wagner said that despite assurances from scientists at
CERN and around the world, there was no proof a mini-black hole would disappear.
No one has ever seen it happen, said Wagner, who studied cosmic ray physics
at UC Berkeley as a young man.
It's just as possible that the tiny black hole would be stable and start chewing
up normal matter, he said.
It could take years for it to become large enough to gobble up the Earth, but
there's no evidence that can't happen, he said.
His suit for a restraining order is to "preserve the status quo while
the court considers the arguments. In this case, the status quo is Mother Earth
being here," he said.
Another nightmare possibility is that the collider could produce something
called strange matter, a theoretical substance that some physicists think exists
in the center of the remnants of collapsed stars.
The pressure and temperature are so intense that the protons and electrons
fuse into neutrons, then collapse into a mass of quarks.
Theoretically, the tremendous gravity of strange matter would convert any ordinary
matter it came in contact with.
Mangano said he is now writing a report addressing such concerns. He said that
protests of physics experiments were nothing new.
"Before each new accelerator started, there has been some panic,"
he said. Wagner, in fact, filed suit in 1999 to stop Brookhaven National Laboratory's
Relativistic Heavy Ion Collider in New York. It went ahead and the world survived
- just as it will this time, according to scientists from Mangano to Newman
and Stephen Hawking.
"Look," Mangano said, leaning forward in his chair at CERN's sprawling
complex, "what if I told you tomorrow when you shave you will blow up the
world? You laugh. You say that can't happen. But how do you know?
"The only thing we know is that there have been about a million billion
shaves since people started shaving and the world is still here," he said.
"So all we can say is the probability of you blowing up the world when
you shave tomorrow is less than one in 1015."
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