This is what is bugging me at the moment: What determines if a particle striking another particle will become a combined wavefunction of probabilities or both of them will collapse, is it probabilistic weather it combines or collapses? I also heard scientists were able to create an atom on two places, so all the protons and electrons in it had a combined wavefunction acting probabilistically, and even made molecules create a wave of probabilities that interfered with itself in the double slit experiment. So what determines when a many particle system either collapses or does not? is it based on the more particles/mass the more likely it is to collapse? Like in the schrödningers cat, the cat was also a part of the wave function, and was in all states until it was determined, So they came up with many world theory and such, seems like ********. I'm pretty confused, about what can tell when a wavefunction collapses and why we need the many world theory. Also the köbenhagen interpertation also seems odd becuase it states something like every wave function combines to create a probabilistic many state system. I've heard it's a fuzzy thing but I can't seem to find the boundraries where wavefunctions start collapsing and stop combining with each other, is it all based on probabilities?