Physicists
around the world have something to celebrate this Christmas. Two groups of
them, using the particle accelerator in Switzerland, have announced that they
are tantalizingly close to bagging the biggest prize in physics (and a possible
Nobel): the elusive Higgs particle, which the media have dubbed the "God
particle." Perhaps next year, physicists will pop open the champagne
bottles and proclaim they have found this particle.
Finding
this missing Higgs particle, or boson, is big business. The European machine
searching for it, the Large Hadron Collider, has cost many billions so far and
is so huge it straddles the French-Swiss border, near Geneva. At 17 miles in
circumference, the colossal structure is the largest machine of science ever
built and consists of a gigantic ring in which two beams of protons are sent in
opposite directions using powerful magnetic fields.
The
collider's purpose is to recreate, on a tiny scale, the instant of genesis. It
accelerates protons to 99.999999% the speed of light. When the two beams
collide, they release a titanic energy of 14 trillion electron volts and a
shower of subatomic particles shooting out in all directions. Huge detectors,
the size of large apartment buildings, are needed to record the image of this
particle spray.
Then
supercomputers analyze these subatomic tracks by, in effect, running the video
tape backwards. By reassembling the motion of this spray of particles as it
emerges from a single point, computers can determine if various exotic
subatomic particles were momentarily produced at the instant of the collision.
The theory
behind all these particles is called the Standard Model. Billions of dollars,
and a shelf full of Nobel Prizes along the way, have culminated in the Standard
Model, which accurately describes the behavior of hundreds of subatomic
particles. All the pieces of this jigsaw puzzle have been painstakingly created
in the laboratory except the last, missing piece: the Higgs particle.
It is a
crucial piece because it is responsible for explaining the various masses of
the subatomic particles. It was introduced in 1964 by physicist Peter Higgs to
explain the wide variation. Until then, a theory of subatomic particles had to
assume that the masses of these particles are zero in order to obtain sensible
mathematical results. This was a puzzling, disturbing result, since particles
like the electron and proton have definite masses. Mr. Higgs showed that by
introducing this new particle, one could preserve all the correct mathematical
properties and still have non-zero masses for the particles.
While
physicists cannot yet brag that they have found the Higgs particle, they have
now narrowed down the range of possible masses, between 114 and 131 billion
electron volts (over a hundred times more massive than the proton). With 95%
confidence, physicists can rule out various masses for the Higgs particle
outside this range.
Will
finding the Higgs boson be the end of physics? Not by a long shot. The Standard
Model only gives us a crude approximation of the rich diversity found in the
universe. One embarrassing omission is that the Standard Model makes no mention
of gravity, even though gravity holds the Earth and the sun together. In fact,
the Standard Model only describes 4% of the matter and energy of the universe
(the rest being mysterious dark matter and dark energy).
From a
strictly aesthetic point of view, the Standard Model is also rather ugly. The
various subatomic particles look like they have been slapped together
haphazardly. It is a theory that only a mother could love, and even its
creators have admitted that it is only a piece of the true, final theory.
So finding
the Higgs particle is not enough. What is needed is a genuine theory of
everything, which can simply and beautifully unify all the forces of the
universe into a single coherent whole -- a goal sought by Einstein for the last
30 years of his life.
The next
step beyond the Higgs might be to produce dark matter with the Large Hadron
Collider. That may prove even more elusive than the Higgs. Yet dark matter is
many times more plentiful than ordinary matter and in fact prevents our Milky
Way galaxy from flying apart.
So far,
one of the leading candidates to explain dark matter is string theory, which
claims that all the subatomic particles of the Standard Model are just
vibrations of a tiny string, or rubber band. Remarkably, the huge collection of
subatomic particles in the Standard Model emerge as just the first octave of
the string. Dark matter would correspond roughly to the next octave of the
string.
So finding
the Higgs particle would be the beginning, not the end of physics. The
adventure continues.
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