Then another, and another. These light-detecting orbs come to rest suspended in the pitch-dark depths down as far as 4,000 feet below the surface. The cable carrying them holds 36 such orbs, spaced 50 feet apart. There are 64 such cables, held in place by anchors and buoys, two miles off the southern coast of this lake in Siberia with a bottom that is more than a mile down.

This is a telescope, the largest of its kind in the Northern Hemisphere, built to explore black holes, distant galaxies and the remnants of exploded stars. It does so by searching for neutrinos, cosmic particles so tiny that many trillions pass through each of us every second. If only we could learn to read the messages they bear, scientists believe, we could chart the universe, and its history, in ways we cannot yet fully fathom.

“You should never miss the chance to ask nature any question,” said Grigori V. Domogatski, 80, a Russian physicist who has led the quest to build this underwater telescope for 40 years. After a pause, he added: “You never know what answer you will get.” It is still under construction, but the telescope that Dr. Domogatski and other scientists have long dreamed of is closer than ever to delivering results. This hunt for neutrinos from the far reaches of the cosmos, spanning eras in geopolitics and in astrophysics, sheds light on how Russia has managed to preserve some of the scientific prowess that characterised the Soviet Union.

The Lake Baikal venture is not the only effort to hunt for neutrinos in the world’s most remote places. Dozens of instruments seek the particles in specialised laboratories all over the planet. But the new Russian project will be an important complement to the work of IceCube, the world’s largest neutrino telescope, an American-led, $279 million project that encompasses about a quarter of a cubic mile of ice in Antarctica.

Using a grid of light detectors similar to the Baikal telescope, IceCube identified a neutrino in 2017 that scientists said almost certainly came from a super-massive black hole. It was the first time that scientists had pinpointed a source of the rain of high-energy particles from space known as cosmic rays — a breakthrough for neutrino astronomy, a branch that remains in its infancy.

The field’s practitioners believe that as they learn to read the universe using neutrinos, they could make new, unexpected discoveries — much as the lensmakers who first developed the telescope could not have imagined that Galileo would later use it to discover the moons of Jupiter. “It’s like looking at the sky at night, and seeing one star,” Francis L. Halzen, an astrophysicist at the University of Wisconsin, Madison, and the director of IceCube, said, describing the current state of the hunt for the ghostly particles.

Early work by Soviet scientists helped inspire Dr. Halzen in the 1980s to build a neutrino detector in the Antarctic ice. Now, Dr. Halzen says his team believes it may have found two additional sources of neutrinos arriving from deep in space — but it is difficult to be certain, because no one else has detected them. He hopes that will change in the coming years as the Baikal telescope expands.