The deep, dark heart of the antimatter

By Sheilla Jones

The Globe and Mail

Saturday, March 8, 2008
Page D10
 

THE MYSTERY OF THE MISSING ANTIMATTER

By Helen R. Quinn and Yossi Nir

Princeton University Press

292 pages

A few years back, I was with a group of Cambridge University particle physicists, astronomers and students in the back garden of a pub on a warm summer night, sipping pints of good British ale and debating the next big breakthrough in physics. Since some of us had just returned from CERN, the giant particle accelerator that straddles the border between Switzerland and France, the implications of discovering new particles was very much on our minds.

But what impact, we wondered, would the discovery of a whole bunch of exotic new particles have on the world? Why would anyone who is not a physicist care if new experiments could finally explain, for instance, why there is now such an imbalance between matter and antimatter in the universe when there was, in theory, an equal amount of both at the time of the Big Bang? The humbling answer is that most people wouldn't care, simply because it would have little noticeable impact on the politics, philosophy or economy of the world, and no tangible effect on everyday life.

When I started reading The Mystery of the Missing Antimatter, I was very much hoping that authors Helen Quinn and Yossi Nir, both particle physicists, had come up with a tale that would make the matter-antimatter mystery ... well, matter. But it was not to be. The authors have, however, done a superb job of explaining why people in their line of work do care, and care a lot.

Quinn, a professor at Stanford Linear Accelerator Centre (SLAC) in California, and Nir, a physicist at the Weizmann Institute of Science in Israel, have spent their professional careers trying to iron out the kinks in the Standard Model of particle physics. Quinn got her start at Harvard in 1970 when, pregnant and unemployed, she offered to work without pay if she could be part of the particle physics team led by Sheldon Glashow (who won the Nobel Prize for physics in 1979). It took about a year, but she was finally offered a post-doctorate position, with pay.

Nir was but a post-doc at SLAC in the late 1980s when he was asked to explain some important new discoveries he was working on to the famed Russian physicist and Nobel laureate Andrei Sakharov, not long after the ailing Sakharov was finally allowed to leave Russia. "This was," Nir admitted ruefully, "by far the poorest presentation that I gave in my life." Such personal insights into the world of particle physicists are, unfortunately, just about as rare in their jointly written book as is antimatter in the universe, which is to say, very rare.

The Standard Model to which both Quinn and Nir have devoted so much of their lives was more or less firmed up by 1976, and for the past three decades, particle physicists have been trying to clear up some of its more vexing mysteries. It cannot, for instance, explain dark matter or dark energy, nor have scientists been able to incorporate gravitational force into the model. The Standard Model does, however, quite successfully explain almost all interactions in the visible universe between the fundamental particles of quarks and leptons (such as electrons and neutrinos) via the electromagnetic, weak and strong forces.

In this model, every particle has a mirror antiparticle partner with the opposite charge. But when such a matter particle meets its antimatter partner, they promptly annihilate each other, giving off a burst of high-energy radiation. Alternatively, the matter-antimatter pair can be created via high-energy collisions. In theory, there should be just as many anti-protons, say, in the universe today as there are regular protons, since they are created and annihilated in pairs. But it turns out that there are almost no anti-protons around, otherwise there would be no stable matter left for the development of stars, galaxies or pub gardens. So where did all the antimatter go?

That's the puzzle Quinn and Nir address in The Mystery of the Missing Antimatter. Ostensibly, the story is treated as a detective mystery, complete with a shadowy, 1950s-vintage detective with a magnifying glass on the book cover. But the story is really a thorough explanation of particle physics and the development of the Standard Model—with its many twists and turns—written in an almost maternal voice that would appeal to many an undergraduate student. Quinn and Nir never resort to dumbing down this complicated and meaty topic, nor do they ever come across as patronizing or condescending. They avoid the use of equations and return to various themes over and over to reinforce them to the reader, but every once in a while, a reader can be excused for becoming lost in a sea of muons and mesons, pions and positrons, strange quarks and bottom quarks. Still, the "we're detectives trying to solve a mystery" theme seems almost an afterthought, an attempt to make particle physics seem sexy.

Quinn and Nir do not solve their mystery, but they do point to some possible suspects. It turns out that not all partners in matter-antimatter pairs behave exactly the same, which could mean that some tiny asymmetry in particle-antiparticle creation and annihilation when the universe was very new and very hot could have led to the much larger asymmetry seen today, when the universe started cooling down. But to figure out what might have happened—and to which particles—requires a powerful-enough particle accelerator to replicate the first few instants of the universe, and that is far beyond what scientists can even imagine building in the next several hundred years.

Fortunately, the Large Hadron Collider at CERN might just be able to provide some clues, if not answers, to help solve the matter-antimatter mystery. Physicists will use the LHC to smash beams of protons into each other. The protons will be travelling at almost the speed of light, and will circle the 27-kilometre underground beam tunnel 11,000 times per second. The idea is to crash opposite travelling beams into each other at one of the five enormous detectors located around the ring, thereby replicating—in theory—the annihilation and creation of particles when the universe was extremely hot and dense and already a fraction of a second old. Quinn and Nir got their book out just in time. The LHC is just about finished and will be put to work—all things going well—in May, and any early discoveries could confirm or confound the ideas the authors have presented as solutions to the mystery.

This is not really a book for the casual popular science reader, but it is one of the best books I've come across for the curious (and tenacious) non-physicist who wants to get a handle on the particles that make up the universe and how they interact. I'd also highly recommend it to any physics undergraduate contemplating the subject. In fact, I'd recommend reading The Mystery of the Missing Antimatter before studying particle physics, again after a couple of courses, and once again after graduation. There is a lot in this book, and more can be absorbed with each reading, however the mystery is ultimately resolved.

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