I'm not an expert in this area, so please feel free to correct me if I've made a mistake or am completely and utterly wrong. From what I understand, the Many-W

I'm not an expert in this area, so please feel free to correct me if I've made a mistake or am completely and utterly wrong. From what I understand, the Many-Worlds Interpretation is, in effect, the "default" hypothesis, insofar as that it follows naturally from state evolution according to the Schrodinger equation. The burden of proof is on the Copenhagen Interpretation to provide some additional mechanism which destroys the quantum states we don't observe. Take, for example, the double slit experiment with a single photon. If we don't measure which slit it passes through, it has the pure state which we can describe as (|left> + |right>), and you can solve the equations with space and time to see that |left> and |right> overlap after they diffract past the slits, so you get an interference pattern. If you measure which slit it passes through, the photon's states get entanged with the experimental apparatus. For example, |left> is now entanged with the left detector resistering its passing, which causes an electric current to a display, which causes photons to be emitted, which interact with the laboratory, and some of which register on our retinas, which cause our neurons to be in a different state, etc.. So the wavefunction is now: |left, measured-left, brain-saw-apparatus-say-photon-went-left, ...> + |right,...> The photon is now thoroughly entanged with the state of our brain and the entire laboratory, so when the photon diffracts after the slit the two states |left,...> and |right,...> no longer overlap and can't interfere. It's much the same thing as EPR, except rather than (|0> + |1>) getting entangled with a second particle to produce (|0,0> + |1,1>), it gets entangled with all the many degrees of freedom of the laboratory, and our brain, and the entire world. Postulating that if we observe |left, ...> then |right, ...> no longer "exists" is entirely analagous to particle B in EPR "observing" that if it is in the state |0,0> then |1,1> no longer exists.