Many-worlds interpretation

An interpretation retaining universal unitary evolution of the quantum state, with definite measurement records described relative to outcome branches. Quantum decoherence explains the practical isolation and stable record basis of emergent branches. It does not insert a physical collapse selecting just one component. The emergence of branch structure and justification of Born rule weights involve additional interpretive arguments beyond writing the Schrödinger equation.

Uncertainty about which observer-centred situation is one's own, even conditional on a known global wave function. An example is a post-measurement observer who has not yet consulted a decohered record. This proposal distinguishes uncertainty about the experienced record from randomness in the universal dynamics. A further argument is needed to connect its credences to branch weights; not every decision-theoretic Everettian account must interpret its weights as ignorance of a uniquely selected future branch.

For an orthogonal decomposition $\Psi ={\sum }_i{\Psi }_i$, the squared norms add to the total norm. Refining one component into orthogonal subcomponents preserves its total weight by the Pythagorean theorem. In an Everettian account these weights are candidates for governing probabilities, rational credences or decisions; the algebra alone does not select which interpretive role is justified. Counting arbitrarily refined components is not the same measure.^[ref]