I came across this statement by bhobba in another thread and it got me to thinking, if the "environment" itself is capable of collapsing the wave function, then how is it possible to produce an interference pattern in a double slit experiment? After all, the particle isn't traveling through a vacuum. It's traveling through, and doubtlessly interacting with, a vast multitude of air molecules on its path from the emitter to the screen, yet none of these interactions seem to be capable of collapsing the wave function. So why doesn't the environment collapse the wave function in a double slit experiment? Why is the environment capable of collapsing the wave function in some cases, but not in others?