Physical theories, eternal inflation, and the quantum universe

Abstract

Infinities in eternal inflation have long been plaguing cosmology, making any predictions highly sensitive to how they are regulated. The problem exists already at the level of semiclassical general relativity, and has a priori nothing to do with quantum gravity. On the other hand, we know that certain problems in semi-classical gravity, for example physics of black holes and their evaporation, have led to understanding of surprising, quantum natures of spacetime and gravity, such as the holographic principle and horizon complementarity.In this paper, 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.

Search optimization, funnel topography, and dynamical criticality on the string landscape

“…The minimal MFPT compatible with recurrence is achieved in d = 2, the critical dimension for recurrence/transience. As a proof of principle, the desired critical scaling (69) can arise in the following simplistic situation. Consider a funnel-like region of the landscape with effective dimensionality D. Suppose that the potential energy is described by a smooth power-law envelope V (ρ) ∼ ρ n , where ρ is the distance in moduli space, punctuated by a lattice of metastable vacua that are equally spaced on average.…”

Spacetime and universal soft modes: Black holes and beyond

“…This problem was addressed in Ref. [49], in which it was argued that the general relativistic, global spacetime as in Fig. 1 should (only) be interpreted as a pictorial depiction obtained by "patching" possible different semiclassical spacetime histories one can obtain in a quantum mechanical world, and that each of these histories describes only the spacetime region a single "observer" (timelike curve) can access.…”

“…In cosmology, the former situation is realized in the scenarios in Refs [49,57]. while the scenario in Ref [58].…”

Cosmological constant: Relaxation vs multiverse

“…Despite these drawbacks and difficulties many authors tried addressing the issue (see e.g. [21,[23][24][25][26][27]).…”