A comment about the cosmology on a bubble wall
Abstract
The interface between a big bubble of true AdSD vacuum expanding inside a false AdSD vacuum is a model of an inflating D-1 dimensional universe. It looks like an interesting setup to study fundamentals of inflation. A recent computation shows that the prediction of this model for the wavefunction of the universe disagrees with that of Hartle and Hawking. We show that this discrepancy is because the effective D-1 dimensional description of the model is spin-0 (Nordstr\"om) gravity rather than spin-2 (Einstein) gravity.
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