Tomorrow, in Philadelphia, Queen's University professor Arthur B. McDonald is scheduled to receive a half-share of the Benjamin Franklin Institute's annual physics prize. It is the latest in a long series of honours for Prof. McDonald, who was the director of the Sudbury Neutrino Observatory (SNO). As one of the oldest internationally recognized honours for research achievements, the Franklin Medal puts him on an altogether new plane, amidst what the French call les nobelisables.
The scientific prestige surrounding the SNO, which ceased collecting data in November of last year, is still growing. As an experiment, it performed exactly as promised, and in an environment of institutional cost-cutting, it did so at a cost (about $70-million) much lower than that required by other particle-physics projects around the world. For every plaudit the SNO receives, there are hundreds, perhaps thousands of Canadians eligible for a share of reflected glory. They ranged from the dozens of physicists who worked on the data-crunching, to the federal bureaucrats who recognized SNO's value and steered clear of it with their budget axes, to the executives at Inco who arranged to set aside space for the project a mile and a half down in the company's Creighton Mine. And let's not forget the miners, who went down into the pit with physicists every day, and during a 1997 strike allowed them to cross a picket line in order to continue their work.
All this was done in the name of hunting the elusive neutrino, a subatomic particle that has no electrical charge and that passes through almost all matter without being stopped or deflected. The existence of neutrinos had been predicted in 1930, and they were first detected in nature as early as 1956, but 40 more years of research had left scientists uncertain whether they possessed any mass. Meanwhile, the sun's interior, a naturally occurring fusion reactor, seemed to be producing only about one-half to one-third as many neutrinos as the so-called Standard Model of particle physics predicted.
The "solar neutrino" problem was a big one. It seemed that scientists would either be required to revise their existing inferential images of the sun's interior, or to do away with the Standard Model itself. For a while it seemed possible that the sun was a lot cooler on the inside than anyone had thought, a discovery that would have had consequences for the ultimate fate of the solar system. Fortunately, when physicists began looking for ways the Standard Model could be modified to allow for the mysteriously low rate of solar neutrino emissions, they realized that if neutrinos did have mass, they were capable of flipping freely in space between three different "flavours" --only one of which earlier neutrino observatories had been capable of observing.
On June 18, 2001, the SNO -- basically a giant tank of heavy water surrounded by cameras that could detect the "flash" created by a single neutrino penetrating to the Earth's core -- solved all of these problems with the release of just one batch of results. It turned out that neutrinos do have mass, that Earth is receiving all three types of neutrinos from the sun and that the total number agrees with established models. Nobel laureate John Bahcall described the discovery in 2004 as "epochal", "revolutionary" and the "fingerprints on the smoking gun" of the solar-neutrino problem.
In the future, the discoveries that the SNO made possible may be placed on a par with Ben Franklin's own research into electricity. Already "neutrino astronomy" is an important field; detectors like SNO will give astronomers early warning of the next supernova in our galactic neighbourhood. As the SNO's "smoking gun" showed, neutrino detection is like having an extra sense to work with when it comes to understanding the solar core. And futurists are spinning wild ideas for neutrinobased imaging and telecommunications -- ideas that now seem as far-fetched, but just as tempting, as alternating current would have been to Franklin.