Neutrinos are teeny-tiny, virtually massless particles that move at speeds close to light. They are very numerous in the cosmos, and can flow through lead as readily as humans do through air, thanks to dramatic astronomical events like exploding stars and gamma ray bursts. They are, however, extremely difficult to track down.
“When you come down to it, neutrinos are extremely weird particles,” says John Conway, a physics professor at the University of California, Davis. “They have essentially little mass and no electric charge, therefore they’re nearly nothing… They’re little more than a few whisps of virtually nothing.” They’re known as “ghost particles.”
They are, nevertheless, an important component of the cosmos, and they have aided scientists in understanding some of physics’ most basic concerns.
According to Dan Hooper, a physicist at Fermi National Accelerator Laboratory and an associate professor of astronomy and astrophysics at the University of Chicago, if you raise your palm toward the sun for one second, roughly a billion neutrinos from the sun will pass through it. This is because they are ejected as a consequence of the sun’s nuclear fusion — the same process that creates sunlight.
“They’re critical to our knowledge of the processes that occur in the sun, as well as an essential component of nature’s pattern,” Hooper said.
Neutrinos were formerly thought to be massless by particle physicists. However, in the 1990s, a group of Japanese scientists determined that they indeed contain some mass. This little amount of mass might explain why the cosmos is composed of matter rather than antimatter. According to Conway, there were equal quantities of matter and antimatter early in the Big Bang process. “However, matter and antimatter were largely destroyed as the cosmos expanded and cooled. In addition, there was a tiny imbalance that favored matter over antimatter. We believe neutrinos may play a role in this process…. It’s also a mystery why we’re constituted of matter rather than antimatter.”
Neutrinos are tough to study. They’re difficult to detect since they interact with other particles so seldom. However, the recently finished IceCube Neutrino Observatory in Antarctica will examine neutrinos within a cubic kilometer block of ice. Here’s how it works: neutrinos contact with atoms within the deep arctic ice detectors, which results in energy puffs.
“As neutrinos flow through and interact, charged particles are produced, and charged particles passing through the ice emit light,” Conway said. “That’s how they’re found out.” It’s like having a neutrino telescope underneath.”
Fermilab National Laboratory has an experiment that sends a beam of neutrinos 400 miles underground in approximately two milliseconds from Wisconsin to Northern Minnesota, and the lab is also working on Project X, a gigantic linear accelerator that will investigate subatomic particles by sending them even farther.
“I wonder if someone would have believed me if I told them the cosmos was filled with massless, chargeless particles with no energy 100 years ago,” Conway remarked. “Who knows where we’ll be in a hundred years.”