The Many-Worlds Interpretation: An Introduction

Interpretation of quantum mechanics which denies the collapse of the wavefunction.

The Many-Worlds Interpretation (MWI) of quantum mechanics is a theory that proposes a very large—perhaps infinite—number of universes exist in parallel to our own. This theory, also known as Everettian Quantum Theory, was first proposed by physicist Hugh Everett III in 1957.

Historical Context and Development

The MWI emerged as a radical solution to the measurement problem in quantum mechanics. The measurement problem arises from the fact that the principles of quantum mechanics seem to break down during a measurement. Before a measurement, a quantum system can exist in a superposition of states. However, after a measurement, the system appears to 'collapse' into one of these states.

Everett proposed the MWI as a way to resolve this problem. Instead of the wave function collapsing upon measurement, Everett suggested that all possible outcomes of the measurement occur in some universe. Each universe is as real as the others, but they are all mutually unobservable.

Understanding the Concept of 'Branching' Universes

The MWI is often described in terms of 'branching' universes. When a quantum event occurs that has multiple possible outcomes, the universe 'branches' into separate universes for each possible outcome. For example, if a quantum particle can be in one of two states, then after a measurement, there will be one universe where the particle is in the first state and another universe where the particle is in the second state.

The Role of the Observer

In the MWI, the observer plays a crucial role. The observer is also subject to the laws of quantum mechanics and can exist in a superposition of states. When an observer makes a measurement, they become entangled with the system they are measuring. This leads to a branching of the observer's universe: in one branch, the observer measures one outcome, and in another branch, the observer measures a different outcome.

In conclusion, the Many-Worlds Interpretation offers a radical but compelling interpretation of quantum mechanics. It resolves the measurement problem by proposing that all possible outcomes of a quantum event occur in some universe. This leads to the concept of 'branching' universes, where each branch represents a different possible outcome of a quantum event. The observer, who is also subject to the laws of quantum mechanics, becomes entangled with the system they are measuring, leading to a branching of their own universe.