The following is an extract from our monthly Launchpad newsletter, in which resident space expert Leah Crane journeys through the solar system and beyond. You can sign up for Launchpad for free here.
We don’t have evidence that wormholes – strange tunnels in space-time – really exist, but they’re so fascinating that I hope they do. There’s some new research on how we might be able to spot them, if they really are out there, and it is wild.
First, let’s be clear: we’ve never seen a wormhole. That could be because they don’t exist or are extremely rare, or it could just be because they’re difficult to spot. In the most basic model of a wormhole, the mouths at either end of the tunnel are black holes. There’d be no way to travel through one of these wormholes – a black hole’s edge is defined by the event horizon, and once anything travels past the event horizon it can never escape. That applies to light, too, so each entrance to this sort of wormhole might just look like a regular black hole, and there would be no exit.
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With the right scientific instruments, though, you could tell the difference between a bog-standard black hole and a wormhole. Close to a black hole, high-energy light is dragged around its edge by the curvature of space-time. A 2022 study found that this would look subtly different near a regular black hole and one that leads to a wormhole – the polarisation of the light emitted in that region would differ. However, we haven’t been able to observe the area that close to a black hole yet, so we can’t use that warped light to tell whether we’ve ever accidentally stumbled upon a wormhole.
There is one other option, though. It only works for traversable wormholes, which are propped open by hypothetical exotic matter that prevents the formation of an event horizon, and keeps the wormhole from collapsing into a black hole. Luciano Combi at the Perimeter Institute in Canada and his colleagues simulated what a traversable wormhole would look like if matter were falling into one end, as it does in active black holes.
The matter falling in would form a ring of matter called an accretion disc around the mouth. But the lack of an event horizon means that light could escape from this sort of wormhole. “As you approach the mouth, it starts to deviate from a black hole,” says Combi. “From the outside, it will be quite similar [to a black hole], but in the centre you will see this very bright shining spot.”
If matter were to fall into the wormhole, it would get stuck in the tunnel, which physicists call the throat. There, it would turn into a blazing hot tornado of plasma, perhaps reaching temperatures hot enough to cause nuclear fusion – it could even turn into a star, although that would almost definitely cause the wormhole to collapse.
Some of that matter could blast out the other end of the wormhole to an entirely different region of space-time at an appreciable fraction of the speed of light. This side of the wormhole would look even stranger: a glowing orb of plasma surrounded by a cloud of hot gas, spewing matter seemingly for no reason. Frankly, it would look crazy. This would be a telltale sign of a wormhole.
I think it’s worth a warning about what would happen if you fell into a wormhole. Depending on its size, you might get spaghettified – your body stretched into noodles – by the powerful gravitational forces. If you were somehow immune to that, the plasma inside an accreting wormhole would immediately incinerate you. Even if the wormhole wasn’t actively accreting matter, just a few tiny particles or a little bit of light would accelerate to such high speeds in the throat that it could blast through you with disastrous consequences. So, if we do someday find a wormhole… probably don’t try to travel through it.
