It is not that neutrinos are not interacting with other matter, but that we cannot observe the interactions. The vast majority of neutrinos spend their lives s

It is not that neutrinos are not interacting with other matter, but that we cannot observe the interactions. The vast majority of neutrinos spend their lives speeding off in a particular direction (from which they started). Only a very, very, very tiny percentage of neutrinos manage to collide with anything and produce a reaction which can then be detected. The way this detector works is that is essentially a gigantic swimming pool of water and periodically there will be an interaction someplace in it which produces a tiny flash of light/radiation which we can then observe. If we could somehow 'see' through the earth or sun, we could observe these same interactions at a much larger scale.