"All around the edge of it," he says. "It was a disk, so whenever you got to the edge, there was a chance you could fall off and into the nothing that existed below."

And that reminds Thor of another story.

"When we were young, all of used to see who'd go closest to the edge and stay there the longest. I always held out the longest. I was scared, but it had been important to me that I'd win."