Still Here After 13.8 Billion Years: The Decay-Rate Bound Implied by the Survival of the Present Vacuum

The present vacuum has not decayed, and that non-event is quantitative information. Approximating the spacetime volume of our past by the Hubble volume times the Hubble time, this paper derives an upper bound on the vacuum decay rate density of 1.02 x 10^-168 GeV^4, and converts it into minimum bounce actions for tunnelling prefactors set by four scales: B of at least 563 for a Planck-scale prefactor, 537 for a grand-unification prefactor, 405 for an electroweak prefactor, and 380 for a QCD-scale prefactor. Relaxing the survival requirement to a one-percent survival probability weakens the bound by less than a factor of five. The paper is a computation from stated assumptions, not a measurement.