Riemann cut

The study of “multiply connected space” actually goes back to Bernhard Riemann. This is when different regions of space and time are “spliced” together. Riemann anticipated the concept of wormholes. Indeed, Riemann was the first to discuss multiply connected space or wormholes. A construction, known as a Riemann cut, connects two sheets of paper together by a line. You make a shortcut on each piece of paper with a pair of scissors. If we walk around the cut, nothing happens, however, if we walk through it, we can move from one plane to the other. It’s a multiply connected surface! This is a wormhole with a neck of length zero: Riemann’s cut.