One of the most puzzling aspects of quantum mechanics is the fact that, when one measures a system in a superposition of multiple states, it is only ever found in one of them.
When a QM state is written concretely enough to make a prediction, it is written on a basis. If it can be written as a single term on a suitable choice of basis, then it is what is known a a pure state. Note that there is no fact of the matter about whether a pure state is superposed, or how it is superposed, unless there is an objective fact about its basis. If the basis is not an intrinsic part of the state, but chosen by the experimenter, or implied by the way the experiment is conducted, then it is unmysterious that when one measures a system in a superposition of multiple states, it is only ever found in one of them.
While understanding basis as a “map” feature helps explain measurement, it undermines coherence-based many worlds, since there is no longer a fact of the matter about how “worlds”, ie states, are organised, or even about where there is more than one.
When a QM state is written concretely enough to make a prediction, it is written on a basis. If it can be written as a single term on a suitable choice of basis, then it is what is known a a pure state. Note that there is no fact of the matter about whether a pure state is superposed, or how it is superposed, unless there is an objective fact about its basis. If the basis is not an intrinsic part of the state, but chosen by the experimenter, or implied by the way the experiment is conducted, then it is unmysterious that when one measures a system in a superposition of multiple states, it is only ever found in one of them.
While understanding basis as a “map” feature helps explain measurement, it undermines coherence-based many worlds, since there is no longer a fact of the matter about how “worlds”, ie states, are organised, or even about where there is more than one.