Doesn the Big Bang theory require space to be flat?
No. To explain the stretching of the universe, the analogy of the surface of a balloon is often employed. Spots on the surface of the balloon grow apart as the balloon stretches while being blown up. Sometimes people infer from this analogy that the shape of space is spherical. However, the interior of the balloon has no meaning in this analogy and, therefore, the surface shape (spherical in this case) is only one possibility for the universe. Here’s a useful way to think about the shape of the universe. Imagine that you’re an astronaut in space and that you have two powerful lasers, one in each hand. You point the lasers so parallel beams from the two lasers shine out ahead of you. If the shape of the universe is flat, the beams continue to travel parallel to each other – forward to infinity. If space is spherical, then the two beams will travel across the curved spherical space of the universe and hit you on the backs of your two hands. Likewise, the saddle shape will cause the two b
