All it takes is one mine, 1,000 tonnes of heavy water, 274 scientists and the backing of an entire town
Arthur McDonald, tall, bespectacled and silver-haired, is hiking down the rocky tunnel of a nickel mine outside Sudbury, Ont., after descending more than two kilometres underground in a mine cage. The space is lit mainly by the roving headlamps worn by his small group. Roof bolts and steel screens brace the rock overhead.
The terrain is uneven, and it’s easy to stumble. McDonald, 72, takes slow, considered steps, occasionally turning to warn the others of a treacherous puddle or ditch. Fatigue is a common side effect of time spent this deep underground, where the air pressure is much higher than above ground, but he doesn’t seem to feel it.
After walking nearly two kilometres, the corridor widens. Here is the entrance to SNOLAB, the world’s deepest clean underground laboratory, where scientists are busy probing the most profound mysteries of the universe.
As a clean lab, the tiniest speck of rock dust, which is naturally radioactive, is forbidden: It could confuse SNOLAB’s ultrasensitive particle detectors. (These detectors benefit from their location deep underground, where layers of rock and earth shield them from cosmic rays.) Before entering, McDonald and his companions, who include Erica Caden, a young particle physicist from Philadelphia, must first give their steel-toed boots a pressure-washing to blast off mud.
Men and women split off into change rooms, strip their mining gear, shower (a soapy scrubbing is mandatory), and don a new wardrobe: lint-free coveralls, goggles and a hairnet. Everyone emerges pink-faced from shower steam into a space that is white, spotless and gleaming—“cleaner than a hospital operating room,” McDonald declares—and a dizzying contrast to the nickel mine outside, one of the dirtiest places imaginable.
There’s something in the superfiltered air at SNOLAB, a sense of anticipation, of validation, as people step forward to greet McDonald. For work performed here, the physicist from Nova Scotia, has just won a Nobel prize. McDonald led an experiment called the Sudbury Neutrino Observatory (fittingly called SNO for short).
In 2002, after years of collecting data, his team demonstrated that bizarre subatomic particles called neutrinos switch from one “flavour,” as physicists call it, to another—there are three types of neutrino—and that they have mass.
Neutrinos are called “ghost particles” because they’re so notoriously impossible to catch: Trillions of neutrinos flow through our bodies and right through the Earth every second, as effortlessly as a sunbeam streaming through a windowpane. These “astronomical messengers,” as McDonald calls them, can tell us about the far reaches of the universe, the explosions of distant stars, even the inner workings of our own sun.
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