Is Cosmology in 300BC? The Search for Alternate Universes with Planck

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In the last few years, we have made remarkable progress in understanding the properties of our observable Universe which appears to have evolved from a hot Big Bang 13.7 billion years ago. The fine-tuning of initial conditions required to reproduce our present day Universe suggests that our Universe may merely be a region within an eternally inflating super-region. Many other regions could exist beyond our observable Universe with each such region governed by a different set of physical parameters than the ones we have measured for our Universe. Collision between these regions, if they occur, should leave signatures of anisotropy in the cosmic microwave background. I will present our analysis of the Planck data which had led to the detection of spectral anisotropies at the location of some high-latitude cold spots associated with the CMB. I will argue that the excess emission may be due to enhanced Hydrogen Paschen-series emission from the epoch of recombination. The strength of the emission would favor a collision with an alternate Universe with a much higher baryon to photon ratio than our own and suggest an anthropic explanation for the value of the cosmological constant. Future, observational tests of this hypothesis will also be discussed.