The odds of this occurring are so extremely low as to cause little-to-no concern, but there is a random chance that in an instant, the entire universe will simply cease to exist. Everything, you and me, stars and planets, entire galaxies would vanish, leaving behind nothing to indicate they ever were there. There wouldn't be- nay, couldn't be any defense or precautions against this, because there's no telling when it would happen. You could be studying, having fun with your friends, or working when it happens. No warnings to the oncoming oblivion.