Physical Theories, Eternal Inflation, and Quantum Universe

TL;DR

This paper proposes a quantum-mechanical framework for the multiverse, unifying eternal inflation and many-worlds interpretations, resolving infinities and paradoxes, and providing a gauge-invariant, observer-centric description of the universe.

Contribution

It introduces a quantum-based, gauge-invariant framework for the multiverse that unifies quantum measurement with eternal inflation and addresses key paradoxes.

Findings

Multiverse described as a quantum state from a single observer's viewpoint

Quantum mechanics regulates infinities in eternal inflation

Framework avoids common measure problems and paradoxes

Abstract

We present a framework in which well-defined predictions are obtained in an eternally inflating multiverse, based on the principles of quantum mechanics. We show that the entire multiverse is described purely from the viewpoint of a single "observer," who describes the world as a quantum state defined on his/her past light cones bounded by the (stretched) apparent horizons. We find that quantum mechanics plays an essential role in regulating infinities. The framework is "gauge invariant," i.e. predictions do not depend on how spacetime is parametrized, as it should be in a theory of quantum gravity. Our framework provides a fully unified treatment of quantum measurement processes and the multiverse. We conclude that the eternally inflating multiverse and many worlds in quantum mechanics are the same. Other important implications include: global spacetime can be viewed as a derived concept; the multiverse is a transient phenomenon during the world relaxing into a supersymmetric Minkowski state. We also present a theory of "initial conditions" for the multiverse. By extrapolating our framework to the extreme, we arrive at a picture that the entire multiverse is a fluctuation in the stationary, fractal "mega-multiverse," in which an infinite sequence of multiverse productions occurs. The framework discussed here does not suffer from problems/paradoxes plaguing other measures proposed earlier, such as the youngness paradox, the Boltzmann brain problem, and a peculiar "end" of time.