Our universe has already experienced a series of profound phase transitions - from the Grand Unified and electroweak epochs to the QCD transition - and it may not be finished yet. The Higgs field could reside in a metastable state, poised to decay into a true vacuum. Tiny black holes or high-energy events could catalyze this transition, creating expanding bubbles of true vacuum racing toward us at nearly the speed of light. In this talk, I will present quantitative predictions for the observable signals such a catastrophic event might generate. We estimate the Higgs particles emitted from a bubble wall, track their decay products, and derive the resulting photon and neutrino energy spectra - possible early-warning signatures that could precede the arrival of the bubble itself. I will then discuss two related scenarios: one involving a TeV-scale colored scalar that breaks SU(3)c and another involving a charged scalar that breaks U(1)EM. In both cases, the first-order phase transition produces distinctive photon and neutrino spectra that could serve as unmistakable fingerprints of an impending vacuum collapse.
