How physically plausible is it that we live in a metastable vacuum?

Answer 1

To the extent that string theory is "plausible", then the idea of living in a metastable vacuum is plausible. A metastable state is one which is locally stable to small perturbations, but does not correspond to the lowest energy configuration possible. String theory supposedly has something like 10^100 possible metastable vacuum solutions, corresponding to all the different possible ways its 11 space-time dimensions can compact or not. If so, the chances of our vacuum being one with the lowest energy is negligible.

The 24 thousand dollar question, then, is how big of a perturbation is needed to knock our vacuum into any of the lower ones? There's no way of knowing, or even making a lower bound based on typical collision events in the universe, since the transition waves is not observable; it travels at the speed of light destoying all observers in its path. Natural selection would only leave those who have not been destroyed by a destabilizing wave (no matter how rare) to ponder such a question.