Can we live in a baby universe formed by a delayed first-order phase transition?

We examine the idea that our Universe began as a baby universe and show that this is feasible in a gauged Uð1Þ_B−L extension of the Standard Model with the classically conformal principle. For the first time, we define a measure to describe the probability that we reside in a baby universe, and find that it can be close to 1 in a considerable portion of the parameter space. The framework is consistent with current cosmological data, and it predicts the existence of a heavy neutral gauge boson, which could be detected at colliders, thereby offering a direct link between early universe dynamics and experimentally testable signatures at the TeV scale.