In essence, though, the difference lies in what happens to the wavefunction during an interaction. In Copenhagen, it collapses, manifesting a single outcome. In MWI, all outcomes are manifest in some universe, and the outcome of a measurement merely tells you which one you're in, broadly speaking.

Originated by US physicist Hugh Everett in the late 1950s, this envisions our Universe as just one of numerous parallel worlds that branch off from each other, nanosecond by nanosecond, without intersecting or communicating.

David Deutsch argues that the way to understand the double-slit experiment is that in each universe the particle travels through a specific slit, but its motion is affected by the interference with particles in other universes. This creates the observable fringes.

The many-worlds interpretation implies that there are most likely an uncountable number of universes. It is one of a number of multiverse hypotheses in physics and philosophy. MWI views time as a many-branched tree, wherein every possible quantum outcome is realized.