When he opened his mouth to speak to someone, they immediately shook their head and scurried off, like rats trying to get off a sinking ship. Not that he was referring to the people around them as rats, far from it. It simply reminded him of the Titanic. The original one, not the starship.
He lifted a hand, not to calm her down, but to close all his fingers but one and point at the tear. "It's in flux. If we were to hop into the TARDIS and pop back through it, there's an astronomical chance of us getting back to our universe. The odds aren't in our favor."
At her question concerning the rip, the Doctor sighed, scanning the tear again, then the area around them, the ground, the sky. "It seems as if this is the end of the universe. Well, not the end. The bottom of it. Did you ever hear the story of Yggdrasil? The Norse believed that the world was part of an immense tree, connecting it to other worlds on different branches. It's very much the same here. Only...we're at the roots." A beat. "It explains why the space through the rip is in flux. Outside of this world, is every other universe possible."