Topics · Space Codex
What is a wormhole?
A wormhole is a theoretical shortcut connecting two distant regions of spacetime.
A hypothetical tunnel through spacetime
At a glance
Key points
General relativity allows such solutions, but holding one open for travel would need exotic matter with negative energy density in amounts never observed. Unlike a black hole, a traversable wormhole would have no event horizon.
- Its mouth would look like a crystal ball showing a distant sky
- A useful thought experiment for teaching curved spacetime
- The 2022 'quantum wormhole' was a simulation, not a tunnel
Where the idea came from
In 1916, months after Karl Schwarzschild's solution of Einstein's equations appeared, Ludwig Flamm noticed that its geometry could be read as a tunnel. Einstein and Nathan Rosen described a 'bridge' joining two sheets of spacetime in 1935, and John Wheeler's group coined the word 'wormhole' in 1957. In 1988 Michael Morris and Kip Thorne asked what a wormhole people could actually travel through would require, partly as a way to teach general relativity.
How it would work
A wormhole has two mouths joined by a throat. The route through the throat can be far shorter than the route through ordinary space, which is what makes it a shortcut. Gravity would normally pinch the throat shut, so it must be propped open by material that violates the 'null energy condition', behaving as if it had negative energy density. Ordinary matter and dark matter cannot do this. Morris, Thorne and Ulvi Yurtsever also showed that moving one mouth could in principle turn a wormhole into a time machine, one reason many physicists suspect nature forbids them.
Common misconceptions
A black hole is not a wormhole. The Einstein–Rosen bridge that appears in the mathematics of an idealised black hole pinches off before even light can cross. A traversable wormhole, by design, has no event horizon, no dark shadow and no accretion disc, so a traveller could turn round and come back. And the 2022 quantum-computer experiment did not create a wormhole: it simulated a small toy model on nine qubits, and even its gravitational interpretation is disputed.
How we would know
No wormhole has ever been observed. A mouth would bend background starlight, and theorists have worked out lensing signatures that would set it apart from a star or black hole; one 1995 proposal suggested looking for the odd brightening a negative-mass mouth would cause in microlensing surveys. Nothing of the kind has turned up. Whether quantum gravity allows large, stable wormholes at all remains an open question.
Related entries
- WormholeA hypothetical shortcut through spacetime
- Black holeEvent horizon · gravity light cannot escape
Sources
- Einstein & Rosen 1935, Phys. Rev. 48:73 (opens in a new tab)
- Morris, Thorne & Yurtsever 1988, Phys. Rev. Lett. 61:1446 (opens in a new tab)
- Jafferis et al. 2022, Nature 612:51 (opens in a new tab)
- Kobrin, Schuster & Yao 2023, critique of the 2022 result (arXiv) (opens in a new tab)
- Morris & Thorne 1988, Am. J. Phys. 56:395 (opens in a new tab)
- James et al. 2015, Am. J. Phys. 83:486 (arXiv) (opens in a new tab)
- Cramer et al. 1995, Natural wormholes as gravitational lenses (arXiv) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.