What electric charge does the neutrino carry?
Right now, trillions of neutrinos from the Sun are streaming through your body every second. You feel nothing. Almost all of them will pass through the entire Earth, 12,700 km of rock and iron, without touching a single atom. How do they get through?
You have all four force profiles. Line them up against one small particle, and the mystery solves itself.
To stop a particle, a force has to be able to act on it. So ask each force in turn: can it act on a neutrino?
The electromagnetic force acts on electric charge. A neutrino has no charge, so the electromagnetic force cannot act on it. The strong force acts on quarks. A neutrino is a lepton, not made of quarks, so the strong force cannot act on it. Only the weak force and gravity remain.
Gravity acts on mass, and a neutrino has almost no mass, so gravity barely acts on it.
The weak force does act on it. But the weak force acts only over distances about the size of an atomic nucleus or smaller. The neutrino must pass almost through the middle of a nucleus before the weak force can act at all.
So almost nothing in matter can act on a neutrino. The two forces that stop ordinary particles cannot touch it, and the two that remain barely act. That is why almost all solar neutrinos pass through the entire Earth untouched, and why trillions pass through you every second without a trace.
A neutrino from the Sun flies into Earth. Check each force in turn: which ones can act on it?
A neutrino carries no electric charge, so the electromagnetic force cannot act on it.
A neutrino is not made of quarks, so the strong force cannot act on it.
Only the weak force and gravity remain.
The weak force acts only over nuclear distances, and gravity barely acts on an almost massless particle.
Only the weak force and gravity can act on it, and both barely act. Almost every neutrino crosses the entire Earth untouched.
A proton flies into the same rock. Why does it stop almost at once?
A proton carries electric charge, so the electromagnetic force acts on it. Every atom it passes exerts electromagnetic forces on it.
A proton is made of quarks, so the strong force acts on it whenever it meets a nucleus.
The proton is gripped almost at once; the neutrino is not. The difference is which forces can touch each one.
Why does the electromagnetic force not act on a neutrino?
Why does the strong force not act on a neutrino?
Which forces can act on a neutrino?
A neutrino detector sits deep underground. Almost every solar neutrino crosses it without leaving a trace. Why?
Imagine a particle exactly like a neutrino, except that it carries an electric charge. Which force would act on it that acts on no real neutrino?
A student says neutrinos cross the whole Earth because they are small enough to slip through the gaps between atoms. Which statement gives the real reason?