I hope this is in the right section of the forum. I figured astrophysics and cosmology could also be acceptable places to ask this. I was watching Lawrence Krauss's talk about everything from nothing, the one with the richard dawkins introduction. He talked about methods for trying to detect dark matter, and he mentioned this one method where germanium atoms were cooled down to a fraction of a degree above absolute zero. If the dark matter particles collided with the germanium atom it would raise the temperature and therefore could confirm the existence of a dark matter particle....or something along those lines. My question is though, if dark matter is able to go all the way through the planet without stopping(Krauss said this), and if the particles could go throughout our body even undetected, then how would it "hit" a germanium atom? I really know almost nothing about particle physics, so I'm sure theres a simple answer.