For more than two decades now, Russian and German physicists have camped on the frozen surface of Lake Baikal from February to April, installing and maintaining instruments to search for the elusive subatomic particles called neutrinos. Artificial eyes deep below the surface of the lake look for dim flashes of blue light caused by a rare collision between a neutrino and a molecule of water. I was told that human eyes would be able to see these flashes too—if our eyes were the size of watermelons. Indeed, each artificial eye is more than a foot in diameter, and the Baikal neutrino telescope, the first instrument of its kind in the world, has 228 eyes patiently watching for these messengers from outer space.
The telescope, which is located a few miles offshore, operates underwater all year round. Cables run from it to a shore station where data are collected and analyzed. It is a project on a shoestring budget. Without the luxury of expensive ships and remote-controlled submersibles, scientists wait for the winter ice to provide a stable platform for their cranes and winches. Each year they set up an ice camp, haul the telescope up from a depth of 0.7 mile, carry out routine maintenance, and lower it back into the water. And each year they race against time to complete their work before the sprigs of spring begin to brush away the Siberian winter and the lake’s frozen surface starts to crack.
What is it about the neutrino that makes scientists brave such conditions? Neutrinos—some of them dating back to right after the Big Bang—go through matter, traveling unscathed from the time they are created and carrying information in a way no other particle can. The universe is opaque to ultraenergetic photons, or gamma rays, which are absorbed by the matter and radiation that lie between their source and Earth. But neutrinos, produced by the same astrophysical processes that generate high-energy photons, barely interact with anything along the way. For instance, neutrinos stream out from the center of the sun as soon as they are produced, whereas a photon needs thousands of years to work its way out from the core to the sun’s brilliant surface.
Neutrinos therefore represent a unique window into an otherwise invisible universe, even offering clues about the missing mass called dark matter, whose presence can be inferred only by its gravitational influence on stars and galaxies. Theory suggests that over time the gravity wells created by Earth, the sun, and the Milky Way would have sucked in an enormous number of dark-matter particles. Wherever they gather in great concentrations, these particles should collide with one another, spewing out (among other things) neutrinos. It is as if a giant particle accelerator at our galaxy’s center were smashing dark-matter particles together, generating neutrinos and beaming them outward, some toward us…