MODERN TIMES

Art Hobson

ahobson@uark.edu

NWA Times 27 October 2007

Particle accelerator goes boldly where none have gone before

If you seek fantastic mysteries, incredible adventures, or strange phenomena, hearken to the astonishing tale of the large hadron collider, or LHC. Located 300 feet below Swiss farmland at Europe's CERN physics center, it will unleash its energies next spring.

It's the world's most powerful particle smasher. Think of a tube 17 miles long, shaped into a huge circle. When the machine is turned on, two narrow streams of protons will flow around the circle, inside the tube, one stream (or "beam") moving clockwise and the other counterclockwise.

Physicists try to figure out what the universe is made of. Ordinary matter is made mainly of three types of particles, called protons, neutrons, and electrons. Every atom of matter has a tiny "nucleus" at the center, made of various numbers of protons and neutrons, and a number of far tinier electrons circling far outside the nucleus. Protons and neutrons are known as "hadrons"--particles made of smaller particles called "quarks"--while electrons might be truly fundamental--not made of smaller particles.

Many more kinds of fundamental particles have been discovered: Ordinary matter seems to be made of six varieties of quarks, three varieties of electrons, three varieties of a radically different kind of particle called neutrinos, and several kinds of so-called "force particles" that cause interactions (pushes and pulls) between the matter particles. And there are anti-matter particles that might be described as the mirror images of all the ordinary particles. All of this has been discovered and organized during the past six decades into a theory called the "standard model of particles and interactions."

Meanwhile, back at the LHC: At a few stations around the circle, the two beams are brought together so that some of the oppositely-moving protons collide. These collisions will occur at the highest energies ever witnessed on Earth: The voltage of each beam is seven trillion volts, so the energy of each proton is seven trillion "electron volts" (or "proton volts"--a proton at a voltage of 7 trillion volts). When two such protons collide head-on, you get quite a physics show.

An incredible thing happens when high-energy particles collide. Out of the surrounding "vacuum" (except for the proton beams, the tube is "evacuated"), the energy of the collision creates a horde of particles of all sorts. This horde of particles will re-create the conditions of the universe during the first trillionth (a decimal followed by eleven zeroes and a one) of a second after the beginning of the big bang that created our universe. Such creation events will occur 30 million times every second at the intersection points between the two beams. Huge particle detection devices located at the intersection points will record the presence and behavior of these particles and spew out enough data to fill 3 million DVDs every year.

Seven times more energetic than the currently largest particle smasher at Fermilab near Chicago, the LHC is exploring broad new realms of the universe. It's hoped that it will create several new kinds of particles and that this will give humankind deeper insight into how the universe got started and what principles maintain it.

The standard model is a frustratingly perfect theory. It hangs together beautifully, and all its predicted particles have been found save one called the Higgs particle. Without the Higgs, the standard model would predict that all particles have zero mass (or heaviness), which is obviously not true. The LHC is energetic enough to find the Higgs particle if it exists. Thus if the Higgs is not discovered, the standard model falls apart and, as one CERN physicist puts it, "we physicists have been talking rubbish for the past 35 years." It's a perfect example of the slender thread of evidence that necessarily challenges every scientific theory: One solid experiment can kill even the most cherished theory. Finding the Higgs, on the other hand, would be the capstone on the standard model.

But it would be boring if only the Higgs is found. This would mean that, at least within the LHC's large range of energies, there's nothing new in the universe beyond the predictions of the standard model.

There are several tantalizing hints that this won't happen. First, astronomers have discovered that nearly all matter in the universe is "dark," meaning it cannot emit or absorb light. We know dark matter exists because its gravity holds galaxies such as our Milky Way galaxy together. This dark matter is presumably made of particles, and these particles will perhaps be created by collisions between LHC protons. Second, theorists have invented an idea called "supersymmetry" that would extend the standard model in a particularly beautiful way; the supersymmetry hypothesis predicts a slew of new kinds of particles. In fact, some of the predicted new particles could turn out to be the sought-after dark matter particles. Third, it's possible that electrons are made of still-smaller particles that the LHC will discover. Fourth, one of the most fantastic hypotheses of modern physics is that extra spatial dimensions, in addition to our ordinary three dimensions, exist and can explain how gravity operates at the tiniest distances. This "string hypothesis" predicts certain new kinds of particles that traverse not only our three dimensions but also the extra dimensions, and it's possible that the LHC could discover some of them. And there will probably be surprises yet unimagined.

We're born with an itch to know that was surely passed down over millions of years of evolution, a yearning that's led us into realms of reality undreamt of by any philosophy. Tune in to the adventure as it unfolds.
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