ManyWorldsInterpretation

The Many-Worlds Interpretation (MWI) of quantum mechanics posits that all possible outcomes of quantum measurements are realized in a vast or perhaps infinite number of branching, non-communicating parallel worlds. Proposed by Hugh Everett III in 1957 as an alternative to the Copenhagen interpretation, MWI eliminates the notion of wavefunction collapse and treats the universal wavefunction as the complete description of physical reality.

According to MWI, the evolution of the universal wavefunction is always unitary; when a measurement occurs, the system becomes entangled with the measuring device and observer, producing a superposition of correlated states corresponding to different outcomes. Decoherence with the environment rapidly suppresses interference between branches, effectively isolating them.

In this view, every possible outcome occurs in some branch, while observers in each branch perceive a definite result. The probabilistic aspect is addressed by deriving the amplitudes of branches from the Born rule, though this is a subject of debate and various approaches exist, such as decision-theoretic proofs.

The interpretation has no unique experimental predictions distinct from standard quantum mechanics, and therefore is not universally accepted. Proponents argue it resolves the measurement problem and eliminates the need for non-unitary collapse. Critics point to ontological extravagance and challenges in explaining probability and the preferred basis problem.

MWI has spawned variants and extensions, including the role of observers (many-minds) and analyses emphasizing decoherence and relative states. It remains one of several interpretations discussed in the philosophy of quantum mechanics.