Why do wavefunctions sometimes combine?

[Jarfi]

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 because 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?

 

[tom.stoer]

Maybe it's interesting for you to study decoherence which explains to some extent the emergence of a "classical world" from quantum mechanical systems.

http://en.wikipedia.org/wiki/Quantum_decoherence
http://arxiv.org/abs/quant-ph/0312059
http://arxiv.org/abs/quant-ph/0105127

 

[Meselwulf]

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 because 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?

They simply couple to each other, interfere. Anyway, a particle collapses it's wave function when there is a disturbance on that wave function. This is a ''measurement'', and it is simply the observation of particles onto other particles, a name which goes by decoherence. Particles never exactly fully hit on each other neither, the fields around the particles effects the presence of other particles which is an interesting fact for some to consider. Particle like electrons never directly hit off each other, either the field they produce effects particles surrounding them or we are talking about a wave function which is interfering with the wave function of other particles.