Hugh Everett’s 1957 interpretation of quantum mechanics, in which the wave function never collapses and every outcome of every measurement is realised in a branch of a continually splitting universal state.
Why it is in this vault
Two of the arguments the site covers run through it. The Simulation Hypothesis makes the sharpest use: the standard objection to many-worlds is that it is monstrously extravagant, and Rizwan Virk’s reply is that it is only extravagant if the branches are physical. As information, branching a world is a routine database operation, so the other outcomes need not exist as universes but as stored, unrendered runs. It is the best original argument in that book. And Closer Encounters argues the opposite way, rejecting both block time and many-worlds in favour of a single revisable timeline, on the ground that moral responsibility requires one.
The physics
It is a live minority interpretation, not a fringe one, and it is empirically equivalent to the alternatives by construction, which is the whole difficulty: nothing observable distinguishes it. Any argument that uses it to license a further conclusion is borrowing the authority of quantum mechanics for a question quantum mechanics does not decide.
Connections
The Simulation Hypothesis · Rizwan Virk · Closer Encounters · Jason Reza Jorjani · Simulation Argument · John Archibald Wheeler · Time-Traveler Hypothesis