The science

A wormhole, if one existed, wouldn't look like a tunnel. Seen from outside, its mouth is a sphere: a crystal ball holding a lensed view of wherever it leads, ringed by a lensed image of our own sky. (The funnel shape in diagrams is that sphere with one dimension left out.)

Einstein's equations allow wormholes. In 1935, Albert Einstein and Nathan Rosen described a "bridge" joining two identical sheets of space, as a model of particles, not a passage. John Wheeler and Charles Misner named wormholes in 1957, and in 1962 Robert Fuller and Wheeler showed that this bridge pinches shut so fast that no signal, not even light, can cross it.

In 1988, Michael Morris and Kip Thorne worked out what it would take to keep one open: material at the throat whose tension is greater than its energy density, called exotic matter, which has negative energy in some reference frames. Thorne took up the question after Carl Sagan asked him for a scientifically believable way to travel for his novel Contact. Negative energy is real in small amounts (the Casimir effect between metal plates less than a micron apart has been measured), but by physicist Matt Visser's estimate a wormhole about a meter across would need about minus one Jupiter's worth of it.

Interstellar's wormhole was built by Thorne and the film's visual-effects team from the same family of geometry as the one ray traced here (an Ellis wormhole). No wormhole has ever been found; searches for their lensing signatures and for gravitational-wave echoes have come up empty.

The animation is a model: an Ellis wormhole, ray traced. Our sky and the other sky are made up.

Imagery: Milky Way panorama: ESO/S. Brunier (CC BY 4.0).