A Universe from Nothing: Why There Is Something Rather than Nothing

by Lawrence Krauss

What do you mean by “flat”? Is the universe flat as a pancake? I wish I had described this a little more carefully in the hardcover edition, and I have expanded the discussion in this edition. A flat three-dimensional space is just the kind of space you already thought you lived in, where light rays travel in straight lines, and perpendicular axes (x,y, and z) remain perpendicular. In curved three-dimensional spaces neither statement is true. Since mass and energy can curve space locally (i.e., around the sun and earth for example), the big question is what about the global structure of space on the largest scales: Is it curved or not? And it turns out on the largest observable scales, it isn’t. And that fact is very telling, as I describe in the book, because it is what one would expect from a universe that arose from nothing.