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Comment by Jem Bishop (jem-bishop) on Many Worlds, One Best Guess · 2023-03-31T12:23:37.044Z · LW · GW

The many worlds interpretation is a vague woolly attempt to paper over the fundamentally paradigm shifting nature of quantum mechanics with a non predictive, but psychologically superficially comforting notion. 
The real "interpretation" is the Copenhagen one, but the word "interpretation" is problematic itself as stated by the founders of QM. There is no need for interpretation as the Born rule is completely sufficient to connect the mathematical part of the theory to physical predictions. https://www.youtube.com/watch?v=85TUPcL7aWQ is one of the few videos of QM on YouTube which really gets this right. The Copenhagen interpretation is really a restatement of this fact. 

The big difference of QM which is different from classical theory, is that classical theory takes for granted an objective reality,  and makes predictions in that framework. QM doesn't and considers the raw principle of science, that science is about giving an individual a framework to predict (probabilities) of future observations. For example in classical mechanics you may say what the probability of a moving particle being at a point x in the future. In QM you talk about the probability of you observing a particle at point x. Superficially they seem the same because we have a brain so accustomed to classical thinking we unconsciously equate them, but they are actually very different. And if you try and shoehorn in quantum concepts into some objective reality framework, which is basically what any "interpretation" is doing, then you will always end up with non-sensical results. Eg if you think of the wave function as being a physical field rather than (roughly) an observers subjective probability distribution, you will quickly get into violations of special relativity. However your own probability distribution updates instantly on new data, so it doesn't have the same issue. 

The many-worlds interpretation at least doesn't lead to breakages of physical laws, but it is so vague and philosophical that it can't really. It doesn't help in deriving the Born rule, and it just adds non-physically testable fluff acting as psychological comfort. If I find the fact that spacetime is curved in GR unpalatable then one could come up with an "interpretation" which reframes it in terms of Newtonian forces, but it would be extra fluff that wouldn't add any predictive power or insight, and I view the many-worlds interpretation the same. What actually is useful is explaining how the classical paradigm emerges as the limit of the quantum one, and that is well understood and  follows from quantum mechanics with the Born rule, no interpretation needed.