I'm still wrestling with the whole uncertainty principal / wave function collapse idea. Obviously a basic building block of QM, I'm having a hard time understanding the real world evidence which supports these QM piles. 1. So from my understanding, the uncertainty principle tells us it is impossible to determine simultaneously both the position and velocity of a particle (lets say a photon). Instead, a 'wave packet' is used to describe the possible position of a photon. The photon may exist in any location of this wave packet. (This is a very general description but please take this as it is for now) 2. Why I'm thinking about this idea now is comparing this note to the double (or single for that manner) slit experiment. If you set up the experiment and turned your light source on and off 1 billion times (without making any changes to the setup) you would see the exact same diffraction pattern 1 billion times, correct? I guess I'm just confused how 1. and 2. both can be correct. 1. tells us that these photons could be anywhere, yet 2. tells us those photons show up at the exact same location on our screen 1 billion times and counting? Thanks for any thoughts.