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The Multiverse Interpretation of Quantum Mechanics by Raphael Bousso and Leonard Susskind
Abstract: We argue that the many-worlds of quantum mechanics and the many
worlds of the multiverse are the same thing, and that the multiverse is necessary to
give exact operational meaning to probabilistic predictions from quantum mechanics.
Decoherence|the modern version of wave-function collapse|is subjective in that it
depends on the choice of a set of unmonitored degrees of freedom, the \environment".
In fact decoherence is absent in the complete description of any region larger than
the future light-cone of a measurement event. However, if one restricts to the causal
diamond|the largest region that can be causally probed|then the boundary of the
diamond acts as a one-way membrane and thus provides a preferred choice of environment.
We argue that the global multiverse is a representation of the many-worlds (all
possible decoherent causal diamond histories) in a single geometry.
We propose that it must be possible in principle to verify quantum-mechanical predictions
exactly. This requires not only the existence of exact observables but two
additional postulates: a single observer within the universe can access innitely many
identical experiments; and the outcome of each experiment must be completely denite.
In causal diamonds with nite surface area, holographic entropy bounds imply that no
exact observables exist, and both postulates fail: experiments cannot be repeated in-
nitely many times; and decoherence is not completely irreversible, so outcomes are
not denite. We argue that our postulates can be satised in \hats" (supersymmetric
multiverse regions with vanishing cosmological constant). We propose a complementarity
principle that relates the approximate observables associated with nite causal
diamonds to exact observables in the hat.