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The theory that our universe is contained inside a bubble, and that multiple alternative universes exist inside their own bubbles -- making up the 'multiverse' -- is, for the first time, being tested by physicists.

Two research papers published in Physical Review Letters and Physical Review D are the first to detail how to search for signatures of other universes. Physicists are now searching for disk-like patterns in the cosmic microwave background (CMB) radiation -- relic heat radiation left over from the Big Bang -- which could provide tell-tale evidence of collisions between other universes and our own.

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So far there is no good evidence, but that may change. - Jack Sarfatti

First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results

Stephen M. Feeney (UCL), Matthew C. Johnson (Perimeter Institute), Daniel J. Mortlock (Imperial College London), Hiranya V. Peiris (UCL)
(Submitted on 16 Dec 2010 (v1), last revised 12 Jul 2011 (this version, v2))
In the picture of eternal inflation, our observable universe resides inside a single bubble nucleated from an inflating false vacuum. Many of the theories giving rise to eternal inflation predict that we have causal access to collisions with other bubble universes, providing an opportunity to confront these theories with observation. We present the results from the first observational search for the effects of bubble collisions, using cosmic microwave background data from the WMAP satellite. Our search targets a generic set of properties associated with a bubble collision spacetime, which we describe in detail. We use a modular algorithm that is designed to avoid a posteriori selection effects, automatically picking out the most promising signals, performing a search for causal boundaries, and conducting a full Bayesian parameter estimation and model selection analysis. We outline each component of this algorithm, describing its response to simulated CMB skies with and without bubble collisions. Comparing the results for simulated bubble collisions to the results from an analysis of the WMAP 7-year data, we rule out bubble collisions over a range of parameter space. Our model selection results based on WMAP 7-year data do not warrant augmenting LCDM with bubble collisions. Data from the Planck satellite can be used to more definitively test the bubble collision hypothesis.
Comments:    Companion to arXiv:1012.1995. 41 pages, 23 figures. v2: replaced with version accepted by PRD. Significant extensions to the Bayesian pipeline to do the full-sky non-Gaussian source detection problem (previously restricted to patches). Note that this has changed the normalization of evidence values reported previously, as full-sky priors are now employed, but the conclusions remain unchanged
Subjects:    Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
Cite as:    arXiv:1012.3667v2 [astro-ph.CO]

Actual article is http://arxiv.org/pdf/1012.3667v2
Category: Science