People have an adverse reaction to the "many worlds" theory. Maybe they don't understand it? Or maybe what I think is the many world interpretation is really so

People have an adverse reaction to the "many worlds" theory. Maybe they don't understand it? Or maybe what I think is the many world interpretation is really something else. Back when I was in theoretical physics we weren't careful about defining terms like this because, as the original comment says, many worlds vs copenhagen was not really an issue of interest, other than in a philosophical sense for people like me. And I didn't take Copenhagen seriously. If you take away any sensient beings, or whatever it is that is required to make one of these "measurements", then copoenhagen is the same as the many world interpretation. Wave functions go on evolving and there is no collapse. For example, an electron can be in spin up or spin down. It is not in both states. In one "world" it is spin up. In another "world" it is spin down. That is strange enough for all of us. But for some reason people have trouble extending this idea to people, so that a person can be in mulitiple states at the same time (in the different "worlds", in the same sense as the electron being in different "worlds".) What made this strike home to me was when I was in graduate school and my advisor told me "There are no magic external observers. The observer is subject to quantum mechanics too. He is part of the experiment." To describe the correspondance between copenhagen and "many worlds", suppose an observer measures if an electron is spin up or spin down. In "many worlds" case his memory of the outcome is correlated with the measured state of the electron. So in the "world" where the electron is spin up (that portion of the wave function) the observer also thinks the electron was measured as spin up. And in the "world" where the electron is spin down, the observer thinks the electron was measured as spin down. In this "many worlds" case, The observer who measures the electron as spin up will not interact with the observer that measured it as spin down. For all intents in purposes, it is as if that other observer never existed. In the copenhagen case, that other observer does _not_ exist. In this interpretation, the wave function collapsed to only include the part with a single observer. In effect the observed outcome of the two interpretations is the same. The difference being one of them, the copenhagen interpretation, postulates a magical change in the wave function of the universe. (Aside - The fact that those observers will not interact is just in a practical sense, to my knowledge. I don't know if it is impossible for them to interact in theory. I don't think it is. Maybe someone else knows the answer to that.)