A wormhole is a tunnel through the fabric of spacetime, an idea expanded by John Wheeler and Kip Thorne. Just as a mountain passage tends to cave in, the throat of a wormhole wants to snap shut. Normally, it's propped open with exotic matter that has negative energy — a substance that pushes space apart, like dark energy. Only we don't have any.

Now, researchers have revisited gravity. Instead of hunting for nonexistent material, they tweaked the equations, adding extra spacetime curvature. Think of an arch bridge: to keep a span from falling, you could prop it with beams you lack, or you can design the arch's curve so it holds itself. Here, the geometry of space is the support. The math checks out: a traversable wormhole (a cousin of black holes) works without exotic matter, and the forces inside are no stronger than Earth's gravity. Sci-fi portals become a far-future engineering challenge.