Aboard a naval vessel in San Francisco Bay recently, Portola Valley resident, Australia native and SLAC physicist Helen Quinn allowed her past to catch up with her.
She had been named an honorary Officer of the Order of Australia two and a half years ago, but there had been no formal ceremony. Protocol requires the medal investiture be done with an Australian military officer present and by someone commissioned by Australia’s governor general, says David Lawson, the local consul general.
The formalities finally came to pass on Nov. 5 during a visit to the Bay Area by the HMAS Sydney, a frigate in the Australian Navy. Mr. Lawson performed the honors on board the Sydney with the lights of the city in the background.
“It worked out very nicely,” he says.
The honor recognizes Ms. Quinn’s contributions to the field of theoretical physics and physics education. She is a member of the nonprofit Contemporary Physics Education Project, a worldwide coalition of educators and physicists. At the Stanford Linear Accelerator Center, her work focuses on the question of why there is more matter than antimatter in the universe.
She is also a wife, mother and grandmother.
A fundamental question
In studying antimatter, the question of symmetry is key. Symmetry is widespread, as can be seen in the shapes of leaves on trees, the even distribution of limbs among life forms, the spherical shape of planets.Tangible everyday stuff like this is made of matter, the particles we have all heard of: electrons, protons and neutrons. But that is not the end of the story. Cosmologists and physicists theorize that these particles have exact opposites made of antimatter. The 1930 discovery of positrons — and later discoveries of antiprotons and antineutrons — established that antimatter exists, Ms. Quinn says.
Electrons (matter) and positrons (antimatter) have opposite electrical charges and tend to annihilate one another when they meet.
A balance once existed, cosmologists say, when matter and anti-matter were equally distributed. Something upset the balance such that the material universe we see today is the excess of matter over antimatter, Ms. Quinn says.
Life is the beneficiary. If balance had persisted and the particles had followed their usual mutual-annihilation behavior, “there would be very little of anything left,” she says.
Thus her focus at SLAC: “When, in the history of the universe, did this imbalance occur,” she says. “How was it allowed to happen”?
To think about this, one must understand the theory on how laws of physics differ for matter and antimatter, she says. “Then we must test that theory,” she adds. “A lot of the work is just understanding the equations, applying them and then figuring out the consequences.”
You also need data. Matter/antimatter collisions usually leave only radiation behind, but at higher energy levels, they may create other informative particle and antiparticle types. Collecting such particles is a challenge given how rare they are, she says.
To improve the odds, the linear accelerator arranges it so that electrons and positrons collide in the emptiness of a vacuum. But out of, say, a million collisions, only a few produce useful results, she says.
“It’s like finding a needle in a haystack,” she says. “And you have to not only find the one in a million case, you have to find many, many examples of it.”
It’s all a mystery, as is evident in the title of her new book: “The Mystery of the Missing Anti-Matter,” co-authored with Israeli physicist Yossi Nir. The intended audience? “Someone willing to concentrate,” Ms. Quinn says.
Educating the public
Explaining physics to non-scientists can be … errr … fun as well as dramatic. One exercise Ms. Quinn says she has done demonstrates the conservation of energy, the first law of thermodynamics. (Note to readers: Don’t try this at home.)In a lecture hall, she suspends a standard bowling ball from a sturdy wire already attached to the high ceiling. She carries the suspended ball to the blackboard — which adds energy to the situation — stands against the blackboard facing the class with the bowling ball taut on the wire and pressed against her forehead, then lets it go and waits without moving for it to return.
The ball swings out over the first few rows of students. It then comes hurtling back toward her forehead, but just kisses it and swings back out. The ball does not gain energy but loses tiny amounts of it from friction in the swinging wire and in air resistance. The pendulum stops when the initial energy quota runs out: energy is conserved.
Faith in the laws of physics may be required to watch unmoving as the ball heads back toward your head. The trick is in the release, Ms. Quinn says.
“You just have to be very careful that you don’t push when you let it go,” she says. “You don’t want to be standing there and wondering ‘Hmmm, did I push that'”?
As a member of the Contemporary Physics Education Project, she has helped design posters on theoretical physics for high schools, though many turn up in college as well, she says. To see examples and read more about cosmology in general, go to cpepweb.org.
