Neutrinos are electrically neutral, extremely [[Light|light]] elementary particles that interact only through the weak force and [[Gravity|gravity]]. Because they almost never interact with matter, enormous numbers pass through Earth (and us) constantly.

## Why they matter
- They are among the most abundant particles in the universe.
- They are produced in the [[Sun]], radioactive decay, [[Supernova|supernovae]], and high-energy cosmic collisions.
- They let us probe environments that [[Electromagnetic Radiation|light]] cannot easily escape.

## Detection
Detecting neutrinos is difficult because interactions are rare. Experiments use huge detectors (deep underground, underwater, or in ice) to catch occasional interaction events.

## Key physics insight
For years neutrinos were assumed massless in early formulations of the Standard Model. Neutrino oscillation experiments showed they change flavor in flight, which implies they have non-zero mass.

That result was major evidence that the original Standard Model description was incomplete.

## See also
- [[Protons]]
- [[Electron|Electrons]]
- [[Science]]
- [[The Big Bang]]