# Meaning of zero probability density

by xfshi2000
Tags: density, meaning, probability
 P: 18 Hi xfshi, in quantum mechanics it's a bit ill-posed to ask if a particle ever arrives' somewhere. The meaningful thing to ask is whether or not you observe the particle. Zero probability density indeed means zero chance of observing the particle in that state (e.g. at that position). It is less meaningful to ask whether the particle actually "does" pass through that point. The probability density doesn't say anything about how a particle got to the position you're observing; e.g. it doesn't tell you if a particle passes through a given point unobserved en route to being observed elsewhere. This is one of the weird and cute features of quantum physics.