LHC Lunch

Meet Sheldon Stone

The particle professor

Syracuse University professor Sheldon Stone jokes that, after the third time teaching quantum mechanics, he finally understood it. As if teaching advanced physics isn’t enough of a challenge, Stone does it with the added complication of a serious commute between the two parts of his job. His classes take place in New York, but his experiment is in an underground cavern near Geneva, Switzerland.

Stone is currently on a year-long sabbatical in Europe to work on site at the LHCb experiment. Like many of his colleagues, Stone considers research his first priority -- after all, that’s why he went into particle physics -- but teaching is a duty just as important. Stone said his time in the classroom is fun, “or it can be.”

Next year he’ll resume the usual schedule of regular trans-Atlantic trips for meetings and research in between his university duties. Next year he’ll also start using video-conferencing software to teach occasional classes from afar rather than substituting a guest lecturer. “If I can sit in the hotel room and meet my class, it’s better for me and them,” he says.

The technique would never fly for a class of 300, he says, but he prefers having small classes with 10 or fewer students anyway. He enjoys teaching advanced topics like quantum mechanics. “You can’t be a particle physicist without [quantum mechanics],” he says, “Of course, everything we do at CERN is in the quantum world.”

Equations in quantum mechanics describe the world of the atom, which behaves differently than the large-scale world of cities and galaxies. One of the better known concepts in quantum mechanics is Einstein’s idea that light exists as both a particle and a wave.

Scientists in the 18th century first observed that shining a light on a metal produced an electric current. This is called the photoelectric effect. They were surprised to find that the energy of the current depended not only on the intensity of the light, but on its wavelength as well.

Particles of light called photons each have a discrete quantity, or quantum, of energy. In the case of the photoelectric effect, incoming photons need a minimum quantum of energy in order to free electrons, the carriers of current, when they hit a metal. What determines this quantum is the light’s wavelength. Too low of a wavelength, and individual particles of light will never have the amount of energy they need knock the electrons from the metal, no matter how many of them are there. “It’s a yes/no thing,” Stone said. “Once you are above the threshold then the current depends on the intensity.”

Light behaves as a coherent wave, but it also has the characteristics of a particle. Quantum mechanics accommodates this seeming-contradiction.

Discoveries in quantum mechanics have implications not only for particle physicists, Stone said, but “most people need it these days.” For one thing, all modern electronic devices are based on quantum mechanical principles. This informs Stone’s classroom approach. As he said, “We teach quantum mechanics so people can learn how to use it, not just so they can appreciate it.”

Although he teaches some of the most complicated classes in physics, he finds the ability to be self-critical, to notice and fix one’s own mistakes, may be the hardest skill to teach. “I don’t want to have to tell [students] the plot’s wrong, I want them to figure it out,” he said. “Eventually they learn it.” He is most impressed, he said, when he tells his students about his own research ideas and they not only point out flaws, but tell him how to make it work anyway.

Stone has just returned from a visit to the U.S. where he learned what he’ll teach when he returns from sabbatical in the fall: particle physics. His favorite.