DAY ONE FRIDAY, AUGUST 2 148/118/24

The blackness was absolute.

Watching over it was Louise Benoit, twenty-eight, a statuesque postdoc from Montreal with a mane of thick brown hair stuffed, as required here, into a hair net. She kept her vigil in a cramped control room, buried two kilometers-“a mile an’ a quarder,” as she sometimes explained for American visitors in an accent that charmed them-beneath the Earth’s surface.

The control room was next to the deck above the vast, unilluminated cavern housing the Sudbury Neutrino Observatory. Suspended in the center of that cavern was the world’s largest acrylic sphere, twelve meters-“almost fordy feet”-across. The sphere was filled with eleven hundred tonnes of heavy water on loan from Atomic Energy of Canada Limited.

Enveloping that transparent globe was a geodesic array of stainless-steel struts, supporting 9,600 photomultiplier tubes, each cupped in a reflective parabola, each aimed in toward the sphere. All of this-the heavy water, the acrylic globe that contained it, and the enveloping geodesic shell-was housed in a ten-story-tall barrel-shaped cavern, excavated from the surrounding norite rock. And that gargantuan cavern was filled almost to the top with ultrapure regular water.

The two kilometers of Canadian shield overhead, Louise knew, protected the heavy water from cosmic rays. And the shell of regular water absorbed the natural background radiation from the small quantities of uranium and thorium in the surrounding rock, preventing that, too, from reaching the heavy water. Indeed, nothing could penetrate into the heavy water except neutrinos, those infinitesimal subatomic particles that were the subject of Louise’s research. Trillions of neutrinos passed right through the Earth every second; in fact, a neutrino could travel through a block of lead a light-year thick with only a fifty-percent chance of hitting something.