Wormholes have been a staple of science fiction for decades L. CALCADA / EUROPEAN SOUTHERN OBSERVATORY / SCIENCE PHOTO LIBRARY

Fancy a trip down a wormhole? We have never been quite sure whether these portals through space-time could exist long enough for anything to travel through. Now calculations suggest they could stick around for a while – perhaps as long as the universe itself.

Wormholes are essentially two black holes connected together. Two types could theoretically exist. A non-traversable wormhole is like a room with two doors that can only be used from the outside – the doors are black holes through which things could enter, but never escape. “These are not very interesting, as any astronaut who is brave enough to venture in won’t be able to make it back to tell the story,” says Diandian Wang at the University of California, Santa Barbara.

Traversable wormholes are also possible, but up until now we didn’t know whether they could exist for long enough for anything to pass through in practice.


For such a wormhole to form, space-time needs to change shape from being like a flat sheet to having holes in it. In classical physics, this can’t happen. But the rules of quantum mechanics seem to allow for space-time to spontaneously change shape, although this is likely to only be for very short periods.

Wang has now worked on a scenario involving string theory, in which the fundamental ingredient of reality are tiny strings. If one of these strings breaks, it can create a traversable wormhole. “It contains energy, and when it breaks, that energy becomes two black holes at each end of the string,” says Wang.

Researchers had shown this was a possibility before, but it seemed the energy would force the two black holes to zoom apart from each other, snapping the wormhole.

Now, Wang and his team have calculated that the curvature of space-time could counteract this acceleration, keeping the black holes static and allowing the throat of the wormhole to remain open. This scenario is extremely unlikely, and becomes even more unlikely the longer the wormhole is and the larger the two black holes are.

Read more: You could survive falling into a black hole but it may get weird

This means that a wormhole big enough for a person to travel through is much less likely than one through which light could be sent. Thanks to quantum mechanics, though, the probability of either happening isn’t zero.

Eternal wormhole

Wang’s team also calculated that, once a traversable wormhole exists, it could remain stable for at least as long as the universe has existed – and maybe forever.

“Our previous work showed that wormholes can be traversable,” says Aron Wall at the University of Cambridge. “But we did not describe a process to create the wormhole.” He says Wang’s calculations show how one could be created from scratch.

Wall points out, however, that Wang’s wormholes couldn’t be used to time travel or move faster than the speed of light. Were you to travel through one, he says, you would still be confined to moving slower than the speed of light.

Journal reference: Classical and Quantum Gravity, DOI: 10.1088/1361-6382/ab436f