Question: How can neutrinos move through you? Are they going through tiny gaps in you or something?

Matthew Malek answered on 10 Mar 2014:

This is a really good question! Hopefully, the answer will help explain how things work a little differently at the subatomic scale.

When two particles come into proximity, there is a finite chance that they will interact. This is based on something called the “interaction strength” of the force responsible for the interaction.

When you push your hand against the desk or a wall or anything, it doesn’t go through because of the electromagnetic force. The electrons in your hand and the electrons in the surface you are touching are repelling each other via the electromagnetic force. The EM force is pretty strong, so you could spend your whole life pressing walls, and your hand will never go through.

In contrast, neutrinos don’t feel the EM force. They don’t feel the strong nuclear force either. All they feel is the weak force, which was named that because it is very weak! So the odds of an interaction when they reach your body is very very small. Trillions of neutrinos pass through you every second — from the sun, from cosmic rays, from exploded stars, and more! Yet odds are that not a single one will ever interact with you.

Like lighr, neutrinos from the sun come down on us from above during the day. At night, the sun still shines but we cannot see the light, as it is blocked by the Earth. Not so for the neutrinos; they pass through the Earth as if it wasn’t there and pass through us coming up from below.

In fact, the US-American poet John Upton wrote a poem about this once, decades ago. It is called “Cosmic Gall” and you can find a copy here: http://users.phys.psu.edu/~cowen/poetry/cosmic-gall.html

(He was wrong about one thing, though — no one knew it at the time, but neutrinos do have mass!)