  Spacetime wormholes can lead to surprises in black hole physics. We show that
a very old black hole can tunnel to a white hole/firewall by emitting a large
baby universe. We study the process for a perturbed thermofield double black
hole in Jackiw-Teitelboim (JT) gravity, using the lowest order (genus one)
spacetime wormhole that corresponds to single baby-universe emission. The
probability for tunneling to a white hole is proportional to $t^2 e^{-2S}$
where $t$ is the age of the black hole and $S$ is the entropy of one black
hole.
