Fastest rockets need 80,000 years to cross 4 light‑years—unless you fold space. Einstein’s equations actually allow wormholes (Einstein‑Rosen bridges).Keeping one open needs exotic matter with negative energy—a big Kip Thorne maybe—and energy rivaling the Sun’s entire 10‑billion‑year output; we’ve never seen any of it.Pull it off and you’d get a black‑hole‑looking portal just miles long that could hop galaxies in seconds and even work as a time machine.