Einstein’s general relativity describes gravity as the bending of space and time. Some of its solutions bend spacetime so much that two distant places connect through a kind of tunnel. That tunnel is a wormhole. Nobody has ever found one, and it is not known whether they can exist, but the mathematics allows them.
A bridge that collapses
The first such solution was found in 1916 by the Austrian physicist Ludwig Flamm, only months after Karl Schwarzschild described what we now call black holes. In 1935 Albert Einstein and Nathan Rosen published their own version, which became known as the Einstein–Rosen bridge. The name “wormhole” came later, from John Wheeler in 1957. The image is of a worm boring through an apple: rather than crawling around the surface, it takes a shortcut through the inside.
In 1962 Wheeler and Robert Fuller showed that an Einstein–Rosen bridge pinches shut so quickly that not even light could get through.
Holding one open
In 1988 Michael Morris and Kip Thorne worked out what a wormhole would need to stay open long enough for something to travel through it. The answer is exotic matter, material with negative energy. That sounds impossible, but quantum physics does allow small regions of negative energy, as the Casimir effect between metal plates shows. Whether enough of it could ever exist in one place is another matter: in 1995 Lawrence Ford and Thomas Roman showed that quantum theory puts strict limits on it.
A time machine?
Also in 1988, Morris, Thorne and Ulvi Yurtsever showed that if one mouth of a wormhole were moved at high speed and brought back, the time difference between the two ends would turn it into a time machine. It could only reach back to the moment the machine was built. Other physicists have argued that quantum effects would destroy a wormhole before that could happen.
The quantum-computer “wormhole”
In 2022 researchers used Google’s Sycamore quantum processor to simulate the dynamics of a traversable wormhole. It was a simulation of the mathematics on a quantum computer, not a wormhole in space.