Armageddon, the end of days, depends in physics on how space is curved overall. Relativity lets space curve but doesn’t specify how it is curved. In mathematics, a positively curved space will eventually stop expanding and contract in a big crunch, but a negatively curved space will expand faster and faster forever because there isn’t enough mass to stop it leading to a big freeze. The latter was expected until cosmology discovered that the expansion of space is accelerating not slowing down (Cowen, 2013), so space is negatively curved.
If our space is the inner surface of an expanding hyper-bubble (2.4.1), it will have the slight negative curvature that cosmology predicts, but that doesn’t mean it will expand forever. If our universe is an expanding bubble in a quantum bulk, there are probably others, so they will eventually meet. What happens when one pocket universe, as Guth calls them, meets another?
The answer depends on whether they are made of matter or antimatter. If one matter universe meets another, they will just merge into a bigger bubble, so if our universe has already done this, it will be bigger than its own expansion allows. The alternative, that our universe meets an antimatter universe, is the Armageddon option.
What then happens when matter meets antimatter? Essentially, they destroy each other, so if a matter universe collided with an anti-matter universe, both would be destroyed to some degree. Antimatter is rare in our universe but is produced tiny amounts by cosmic rays in thunderstorms. It soon vanishes however when it meets matter, some of which probably also vanishes with it. It seems then that if our bubble universe met its antimatter equal, both could annihilate back into the quantum bulk from whence they came.
This Armageddon would spread at light speed but it could take a while, as our galaxy is an estimated 100,000 light years across, and the observable universe is 90 billion light years across. Even so, could our telescopes see it coming? Unfortunately no, as we see galaxies as they were millions of years ago. Our earth would just be there one moment and gone the next. When our world is packed away, it will be at the speed of light, with no possible warning.