I don't think Many Worlds/Universal Wave Function is actually unpopular amongst physicists. There was a survey (I'll have to find it) that showed it was one of

I don't think Many Worlds/Universal Wave Function is actually unpopular amongst physicists. There was a survey (I'll have to find it) that showed it was one of the most popular interpretations. It's appealing for its mathematical simplicity, giving unitary wave function evolution with the reasonable assumption that the universe has a wave function. It eliminates wave function collapse from the axioms, and possibly eliminates the Born rule. Talking about its 'complexity' in the 'creation' of parallel worlds isn't much of an issue, you can look at simple systems like the von Neumann measurement model to see how they naturally arise through superposition. The main issue is how the Born rule arises. That is, why the probability of an 'observer' ending up in a particular branch of the wave function is |psi|^2 isn't clear, but then it isn't clear what probability means in this context...