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.