Here are answers to some of the most frequently asked questions about neutrinos and neutrino research:
Neutrinos are fundamental particles, meaning one of the types of tiny particles that make up everything. In fact, neutrinos are the most abundant particles with mass in the universe. If you hold out your thumb and blink, almost 100 billion neutrinos passed through your thumbnail in that time. However, another important property about neutrinos is that they don’t like to interact much. Even though trillions of neutrinos pass through your body every second, in your entire lifetime only one or two will stop and interact.
Neutrinos are incredibly light and come in three kinds (called “flavors”), named after the particles they produce when they do interact. There are electron, muon, and tau neutrinos. Neutrinos are unique among fundamental particles because they change flavors as they travel—this is one of the reasons they are so exciting to scientists.
Yes! Neutrinos are incredibly safe. Most neutrinos pass through matter without ever interacting. They are very small and neutral (they have no charge), so they don’t often come into contact with other particles. Neutrinos don’t emit radiation or harm the materials they travel through.
Neutrinos are the most abundant massive particle in the universe, but we still know very little about them. Even though they are one of the fundamental building blocks of the universe, we don’t know how much they weigh—or why they have mass at all. Our models predicted they wouldn’t. Neutrinos are a clue to new physics: ways of describing the world that we don’t know yet. They also might have unique properties that would help explain why the universe is made of matter instead of antimatter. Until we know more about these mysterious particles, we won’t know some of the secrets of our universe—or the ways we can harness them for more practical purposes. For more on this, see the FAQ: “What are the benefits of neutrino research?”
Neutrinos are poorly understood, so the current priority is basic research. This tells us more about the particles themselves and how they fit into our picture of the universe. They can also help us better understand larger fundamental physics questions and test our theories about how things work. As with much of basic research, we often don’t know where the research will ultimately lead us. Think of the electron: Early researchers could have no idea that discovering the electron would revolutionize the world, providing us with electronics, computing, and a more connected world. This also applies for much of the technology that is used to build and run physics experiments—no one could have predicted the way the World Wide Web, developed to share physics data, would revolutionize how we communicate, shop, travel, and do a thousand other things.
The same is true for neutrino research. We’re not sure where the technology—the sensitive detectors, powerful particle accelerators, data processors, and other things that make experiments run—will eventually be useful. People are already dreaming up interesting applications for neutrinos and neutrino research. Because neutrinos are so small, wily, and hard to detect, there are many practical hurdles between the current state and implementation. Perhaps the closest to reality is using neutrino detectors to monitor nuclear proliferation for national security. It could also potentially be used to assess Earth’s crust for mineral deposits or provide a new kind of communication. We’re still very much at the beginning of our neutrino journey; what we do with this technology and information remains for the physicists of the future.
Everywhere! Neutrinos are a natural part of particle decay, when one particle transforms into another. Neutrinos can come from within Earth’s core, our sun, explosions of far-off stars, the Big Bang, reactions when particles interact in our atmosphere, or even reactions in your own body. Even bananas produce neutrinos. Scientists can also produce them using accelerator beams or nuclear reactors, creating a controlled source that is more easily studied.
Neutrinos were predicted in 1930 to explain a radioactive process called beta decay. Armed with theories, Clyde Cowan and Frederick Reines experimentally discovered the neutrino in a reactor experiment in 1956. Further experiments revealed different flavors of neutrinos and additional properties. Read more about these experiments in the timeline.
No, they do not. Neutrinos are weird, but they aren’t that weird.
The origin of this misconception comes from a 2011 result. The OPERA experiment data showed neutrinos arriving at the detector surprisingly quickly, supposedly traveling faster than the speed of light. Other experiments in the same neutrino beam (and elsewhere around the world) were unable to replicate the anomaly. The OPERA team later discovered a faulty piece of equipment (a cable) was responsible for the timing mismatch. Once repaired, OPERA also clocked neutrinos as very close to the speed of light, but not surpassing it.
Scientists can use many different kinds of materials to detect neutrinos, from mineral oil and dry cleaning fluid to Antarctic ice and water. Because neutrinos are neutral and so small, it is impossible to detect them directly. Instead, all techniques rely on detecting the heavier, charged particles generated when a neutrino interacts, creating a signature track, flash of light, line of bubbles, change in temperature, or other indicator, depending on the material. Because neutrinos interact so rarely, detectors need to be very big and experiments need to run for long periods to take a lot of data. They must also have systems in place to weed out interactions from other particles that could clutter up neutrino data.
A neutrino beam is one way that physicists study neutrinos. Scientists use particle accelerators to create energetic particles that smack into a target, producing other particles that decay into neutrinos. This creates a concentrated group of neutrinos with a specific flavor and amount of energy. Having lots of information about the kind of neutrinos created makes it easier for researchers to conduct experiments and study the tricky particles.
Neutrinos change flavor as they travel, and how much they change is related to how far they go. Placing detectors at different distances from the source can tell us more about neutrino properties. Comparing how neutrinos and antineutrinos change as they travel long distances can tell us more about how they might differ, which can give researchers insight into how neutrinos and antineutrinos have shaped our universe.
“Oscillations” refer to the way neutrinos change flavor as they travel. A neutrino born as one flavor (electron, muon, or tau neutrino) will eventually morph into the other varieties—and the probability of appearing as a different flavor depends on how far it has gone. Oscillations are a result of quantum mechanics, or the weird way things work at very small scales. Discovering neutrino oscillations was particularly exciting because it revealed to scientists that neutrinos have mass, something the current model couldn’t explain. It’s the first and only evidence that the current model of particle physics may not be complete. That means more fun physics ahead to explain this massive mystery.