April 3, 2006
Quest for truth wins Dimopoulos physics prize
By Krista Zala
Physics Professor Savas Dimopoulos was awarded the 2006 J. J. Sakurai Award for his work in advancing theoretical particle physics. He will be presented with the award at the annual meeting of the American Physical Society on April 24 in Dallas. The citation lauds Dimopoulos for "his creative ideas on dynamical symmetry breaking, supersymmetry and extra spatial dimensions, which have shaped theoretical research, thereby inspiring a wide range of experiments."
The quest for quantifiable natural truth led Dimopoulos to pursue physics from an early age. Amid the boisterous culture of 1960s Greece, he heard politicians spin reality to suit their ideologies. "I wanted a concept of truth that didn't depend on the eloquence of the speaker," recalls Dimopoulos.
When a friend introduced him to calculus at age 14, he seized upon the tool that could predict positions of planets through the ages. He decided that rather than study Platonic philosophy, he would investigate physics, as it uncovers and explains reality as it exists, independent of human interpretation.
After earning a bachelor's degree in physics in 1973 from the University of Houston, Dimopoulos enrolled in the doctoral program at the University of Chicago. His graduate adviser was the renowned elementary particle physicist Yoichiro Nambu, who won the Sakurai prize in 1994. Before accepting the young Dimopoulos as a student in 1976, Nambu warned that jobs in theoretical physics were extremely scarce and that he might never find one. As an adviser, Nambu cautioned that reading too much leads to borrowing other people's modes of thought. "The first day, he tells me, 'Rule number one: Read as little as possible and try to figure things out by yourself.'" Today, Dimopoulos repeats this advice to his graduate students.
Devising testable theories
The Standard Model of particle physics was established in the late 1970s. It describes three forces: electromagnetism; the strong nuclear force, responsible for keeping nuclei from flying apart; and the weak nuclear force, responsible for radioactivity. It appeared to Dimopoulos at the time that all the great work in particle physics was over. Yet the Standard Model failed to explain why a fourth force, gravity, is 40 orders of magnitude weaker than the other three. No proposals adequately addressed this puzzling difference in strength, an issue known as the "hierarchy problem." Dimopoulos decided to heed family advice"Work only on the most important problems. Small things and big things both take time. Big things are worth it and small things are not"and tackle the disparity between gravity and the other forces.
Immediately after graduate school he worked with Stanford physics Professor Leonard Susskind on the first theory to explain the hierarchy problem. Dubbed "Technicolor," it posited that some elementary particles are composites, similar to how protons are made out of quarks.
Spurred by this model, Dimopoulos proposed in 1981 with Harvard physicist Howard Georgi to extend the Standard Model by adding a new fundamental principle called supersymmetry. In the supersymmetric Standard Model, every particleelectrons, photons, quarks and so onhas a corresponding superparticle. This was similar to the proposal of antimatter in the 1920s, which posited that every known particle has an antiparticle. But many physicists ridiculed the proposal and joked that "at least half of the supersymmetric Standard Model had been discovered."
Experiment catches up to theory
In the 1970s, the physics community realized that at extremely high energies, the three strongest forces of nature (electromagnetism, the strong nuclear force and the weak nuclear force) could arise from a single force. This idea was called Grand Unification and predicted the relative strengths of the three forces and hypothesized they were different manifestations of a single overarching symmetry.
Early experiments disfavored the merging of supersymmetry with Grand Unification. More precise measurements at a particle accelerator at a European physics center, CERN, measured the relative strengths of the forces to 1 percent accuracy and found that the union of Grand Unification with supersymmetry is in fact necessary to explain the data. This turn of events bolstered the supersymmetric Standard Model from a mere contender among a handful of proposals to the leading candidate for a new physics model.
In 2007, a particle accelerator under construction at CERN, called the Large Hadron Collider (LHC), will begin colliding particles with the highest energies ever harnessed. It offers the best chance yet of creating supersymmetric particles in the laboratory and directly discovering all the different particles of the supersymmetric Standard Model.
The LHC may prove or disprove the supersymmetric Standard Model. Best of all, Dimopoulos muses, it may uncover a new truth that no one ever dreamed of. "We just want to understand our universe. That's what drives us."
Krista Zala is a former News Service intern.
A photo of Dimopoulos is available on the web at http://newsphotos.stanford.edu.