Bubble collisions and measures of the multiverse

Abstract

To compute the spectrum of bubble collisions seen by an observer in an eternally-inflating multiverse, one must choose a measure over the diverging spacetime volume, including choosing an "initial" hypersurface below which there are no bubble nucleations. Previous calculations focused on the case where the initial hypersurface is pushed arbitrarily deep into the past. Interestingly, the observed spectrum depends on the orientation of the initial hypersurface, however one's ability observe the effect rapidly decreases with the ratio of inflationary Hubble rates inside and outside one's bubble. We investigate whether this conclusion might be avoided under more general circumstances, in particular placing the observer's bubble near the initial hypersurface. We find that it is not. As a point of reference, a substantial appendix reviews relevant aspects of the measure problem of eternal inflation.

24 pages, two figures, plus 16-page appendix with one figure; v2: minor improvements and clarifications, conclusions unchanged (version to appear in JCAP)

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Cited by in corpus (17)

• Self-Locating Uncertainty and the Origin of Probability in Everettian Quantum Mechanics
• How unitary cosmology generalizes thermodynamics and solves the inflationary entropy problem
• Simulating the universe(s): from cosmic bubble collisions to cosmological observables with numerical relativity
• Accidental Inflation in the Landscape
• Simulating the universe(s) II: phenomenology of cosmic bubble collisions in full General Relativity
• Hierarchical Bayesian Detection Algorithm for Early-Universe Relics in the Cosmic Microwave Background
• Multiple Cosmic Collisions and the Microwave Background Power Spectrum
• Super cosmic variance from mode-coupling: A worked example
• The CMB and the measure of the multiverse
• On memory in exponentially expanding spaces
• Observable Signatures of a Classical Transition
• Gravity waves from cosmic bubble collisions
• New Scale Factor Measure
• New Local Duals in Eternal Inflation
• Multiverse rate equation including bubble collisions
• Forecasting constraints from the cosmic microwave background on eternal inflation
• Disentangling the Cosmic/Comoving Duality: The Cognitive Stability and Typicality Tests