If a neutrino do not interact with anything and can pass through a light year of lead, how humans manage to detect them?
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Neutrinos interact via two of the four fundamental forces: gravity and the weak force, which is… well, weak.
When a neutrino passes through a detector, there is a *chance* of it being detected, but that chance is low. Thankfully, there are so many neutrinos passing through earth that some will be detected. What we do is wait for an interaction to happen via the weak force (eg transfering some of its momentum to a nearby electron via the weak force (specifically a W boson)), and then we detect the effects on the things that were interacted with (eg in our example, the electron can be accelerated to relativistic speeds, and so if we put it in heavy water then there will be a flash of light from Cherenkov radiation).
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