People at the Sudbury Neutrino Observatory are looking for answers to some questions that aren’t for the scientifically faint-of-heart. Why is the universe made of matter instead of anti-matter? And where does “dark matter”—the invisible stuff that makes up much of the universe—come from?
Appropriately enough, the answers to these deep questions are coming from a facility deep in the earth. The heart of the observatory is a 12-metre acrylic sphere filled with heavy water and surrounded by an array of light sensors—all immersed in another layer of highly-purified normal water. Located almost two kilometres underground, at the bottom of Inco's Creighton nickel mine, the apparatus is designed to detect particles from space called neutrinos. The rock overhead filters out other kinds of cosmic radiation, but neutrinos slice right through the earth—and those that pass through the heavy water vessel cause a tiny flicker of light, triggering the sensors.
The facility has already answered a question that stumped physicists for thirty years, known as the Solar Neutrino Problem: why does the quantity of neutrinos reaching the earth from the sun not jive with our understanding of how the sun generates energy? Measurements made possible by the pristine conditions at the Sudbury facility finally provided the answer: our model of the sun was correct, but the nature of the neutrinos changed on their journey to the earth. The breakthrough in understanding was named the second-most important science story in 2002 by the international journal, Science.