The CMB and the measure of the multiverse

Abstract

In the context of eternal inflation, cosmological predictions depend on the choice of measure to regulate the diverging spacetime volume. The spectrum of inflationary perturbations is no exception, as we demonstrate by comparing the predictions of the fat geodesic and causal patch measures. To highlight the effect of the measure---as opposed to any effects related to a possible landscape of vacua---we take the cosmological model, including the model of inflation, to be fixed. We also condition on the average CMB temperature accompanying the measurement. Both measures predict a 1-point expectation value for the gauge-invariant Newtonian potential, which takes the form of a (scale-dependent) monopole, in addition to a related contribution to the 3-point correlation function, with the detailed form of these quantities differing between the measures. However, for both measures both effects are well within cosmic variance. Our results make clear the theoretical relevance of the measure, and at the same time validate the standard inflationary predictions in the context of eternal inflation.

28 pages; v2: reference added, some clarifications

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Cited by in corpus (6)

• Inflation after False Vacuum Decay: Observational Prospects after Planck
• A non-Gaussian landscape
• Non-Gaussian Mode Coupling and the Statistical Cosmological Principle
• Super cosmic variance from mode-coupling: A worked example
• New Scale Factor Measure
• Multiverse effects on the CMB angular correlation function in the framework of NCG