A more complicated curvature would be like a function that inputs an entry point and returns one of several local lowest points.

With Roger Penrose I showed that if Einstein's general theory of relativity is correct, there would be a singularity, a point of infinite density and space-time curvature, where time has a beginning.

Spanish entrepreneur wants to give you a glimpse of the black expanse of space and the curvature of the earth from a most unusual vantage point — a balloon.