Although it’s possible that wormholes exist, travel through the theoretical tunnels seems nearly impossible. The wormhole, officially called an  Einstein–Rosen bridge, is a theoretical shortcut between two unique regions of space-time.

This concept is displayed in “Interstellar,” a sci-fi thriller directed by Christopher Nolan that opened in theaters across the country in early November.

Astrophysicist Kip Thorne of the California Institute of Technology in Pasadena, an adviser and executive producer for the film, explained that while wormholes may be possible according to Einstein’s theory of general relativity, the voyages through the tunnels are likely to remain a sci-fi fantasy, at least for now.

Thorne said in a statement, “The jury is not in, so we just don’t know. But there are very strong indications that wormholes that a human could travel through are forbidden by the laws of physics. That’s sad, that’s unfortunate, but that’s the direction in which things are pointing.”

Thorne, a leading expert on wormholes, black holes and relativity, explained that a wormhole’s instability is its major barrier. He explained, “If you don’t have something threading through them to hold them open — the walls will basically collapse so fast that nothing can go through them.”

Wormholes would require negative energy to remain open. Thorne explains that although this energy type occurs in physics, “We have very strong, but not firm, indications that you can never get enough negative energy that repels and keeps the wormhole’s walls open; you can never get enough to do that.”

In 1935, physicists Albert Einstein and Nathan Rosen used the theory of general relativity to propose the existence of “bridges,” or wormholes, through space-time.