Don't be so sure that our universe is flat

摘要

For centuries the ancients believed the Earth was flat. Evidence to the contrary was either ignored or effortlessly integrated into the dominant world view. Today we dismiss flat-Earthers as ignorant, yet we may be making an almost identical mistake - not about our planet, but about the entire universe.rnWhen it comes to the universe, "flatness" refers to the fate of light beams travelling large distances parallel to each other. If the universe is "flat", the beams will always remain parallel. Matter, energy and dark energy all produce curvature in space-time, however. If the universe's space-time is positively curved, like the surface of a sphere, parallel beams would come together. In a negatively curved, saddle-shaped universe, parallel beams would diverge.