Speaker
Description
We use the Euclidean path-integral method to approximate the wavefunction of the universe, focusing on a scenario in which a single Euclidean wormhole instanton dominates the path integral. This solution, which connects two Lorentzian spacetimes, provides an approximation to the emergence of classical spacetime in quantum cosmology. Beyond the background level, perturbations about this instanton are treated quantum mechanically in both the Euclidean and Lorentzian regimes. We show that the initial wavefunction for these perturbations can be fully determined at the free-field level, exhibiting an entangled structure between the two Lorentzian spacetimes. In a fully symmetric setting, we further argue that these perturbations can be understood as a generalization of the thermofield-double-state interpretation of the Unruh effect. Interestingly, we find that this generalization uniquely selects the vacuum state in the Lorentzian spacetimes.