The Super-Kamiokande neutrino observatory seen above, is located in a zinc mine 3,300 feet underground, near the city of Hida, Japan. The walls of the tank are instrumented with 13,000 light detectors, and in this photo you can see workers rowing around the interior as it fills with 50,000 tons of water. Neutrinos are subatomic particle that are notoriously hard to detect because they have no electric charge and they pass right through almost all ordinary matter. In fact, 100 trillion neutrinos apparently flow through our bodies every second. The Super-K observatory pictured here is just one detector that scientists are building to study these "ghost particles" as they're known. From Smithsonian:
So that neutrinos aren't confused with cosmic rays (subatomic particles from outer space that do not penetrate the earth), detectors are installed deep underground. Enormous ones have been placed in gold and nickel mines, in tunnels beneath mountains, in the ocean and in Antarctic ice. These strangely beautiful devices are monuments to humankind's resolve to learn about the universe.
It's unclear what practical applications will come from studying neutrinos. "We don't know where it's going to lead," says Boris Kayser, a theoretical physicist at Fermilab in Batavia, Illinois.
Physicists study neutrinos in part because neutrinos are such odd characters: they seem to break the rules that describe nature at its most fundamental. And if physicists are ever going to fulfill their hopes of developing a coherent theory of reality that explains the basics of nature without exception, they are going to have to account for the behavior of neutrinos.
"Looking for Neutrinos, Nature's Ghost Particles"
