A simulation of the structure of the Universe. If you leave one “edge” of the Universe and return through another, you just might live in a recurrent Universe. (NASA, ESA, AND E. HALLMAN (UNIVERSITY OF COLORADO, BOULDER))

Would A Long Journey Through The Universe Bring Us Back To Our Starting Point?

If you traveled in a straight line for far enough, would you come back to where you started?

If you were to set out on a journey from anywhere on Earth’s surface, and traveled in a straight line for far enough, you’d eventually wind up right back where your journey began. After traversing approximately 40,000 kilometers (25,000 miles) — crossing mountains, oceans, deserts, etc. — you’d have completed one entire journey around the surface of our planet. The eventual destination you’d arrive at would be unambiguous: it’s the same as your starting point.

Could it work the same way in space? If you got into a starship, set off in one direction, and traveled as far as you liked, would you eventually return to your starting point? It’s a fascinating question to explore. Even though all signs seem to point towards “probably not,” there are actually two ways that the answer might turn out to be yes, after all.

The Mesquite Flat Dune field at Death Valley National Park is a spectacular landscape, but even with this level of visibility, we cannot determine the curvature of Earth from simply standing on the ground at this (or any other location) on its surface. (WIKIMEDIA COMMONS USER BROCKEN INAGLORY)

When we step out of our homes and look at the Earth around us, it generally appears to be flat. For as far as we can see in every…