The Scrhödinger's cat experiment is closely related to wave function collapse: A cat is set in a box where there's also a radioactive particle that can decay (or not). If the particle decays, radiation activates a mechanism that releases some poison, killing the cat. As the decay is probabilistic in nature, it's said that, if we leave the box closed, the cat is in a superposition of quantum states, so the cat is dead/alive until we open the box and collapse its wave function.
This experiment shows all the problems that derive from the Copenhagen interpretation:
What is an observer? It seems we have one observer (ourselves) and one wave function (the cat dead/alive) but, in fact, there's a chain of nested observers and wave functions. All problems about who collapses what appear because we use the same wave function when, in fact, each observer at each level would have different wave functions being collapsed at different moments by different interactions.
When do wave functions collapse? All wave functions for the things inside the box are enclosed by another wave function about the box's state, so the nested ones aren't taken into account until we open the box. The cat could be dead by now, but if we don't open the box, it's still in superposition for us. But even if we open the box, our friend outside the room has a wave function waiting for us. So we could go all the way up on this ladder of nested wave functions (reaching the many worlds interpretation), or we could go down and realize that the interaction between the radioactive particle and the poison mechanism (if it happens) would be a "collapsed wave function" already, because carriers can't evolve at c. So you can see our brain's wave functions are not that special to what happens in the universe. We're not that different to any other particle out there, we're just a bunch of emitters and absorbers, participating on the interactions we trigger and detect.
How does collapse happen? There's just one event that can change the cat's state, and that's the particle radiating. Some other exchanges can update our knowledge about the cat's state, but they're not fundamental for its fate. If it were not for us, cat's carriers would be decoded or discarded by any other observers. If we leave the box closed forever, the cat's state will evolve almost the same, but interactions will take place between cat's atoms and box's atoms.
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