The known universe is full of exciting things like black holes, hypernovas, and neutron star mergers. However, all of these seem tame compared to the elements that physicists think might be there but haven’t yet found. Perhaps the most important of these are wormholes, which theoretically connect portions of space and time, allowing those who enter them to shortcut to remote locations.
The possibility of wormholes came as a great relief to science fiction writers, cut off from the star systems they wished to explore by physical laws forbidding faster-than-light travel. Many physicists doubt it exists, or at least that 3D objects can pass through it unscathed, but mere chance was enough for the writers to pilot a spacecraft, or at least retell, through it.
And as telescopes advance, the question becomes more troubling: If wormholes are real, why haven’t we found any? Four Bulgarian physicists proposed an answer in Physical Review D: We may have known them and not recognized them.
The vast majority of black holes we have identified are known either from their gravitational influence on the stars around them, or from jets of material shooting out of their accretion disks. If any of these holes are actually wormholes, we’re unlikely to know. However, the Event Horizon Telescope Collaboration’s observation of polarization around M87* and its follow-up on Sagittarius A* is a different matter. In these cases, we saw the shadow of the object itself against its event horizon, and we might hope to notice something if we were actually looking into a wormhole.
The possibility of wormholes is exciting enough for physicists that 12 papers have been published on ArXiv.org exploring the concept since the beginning of November. However, as noted by Petya Nedkova of Sophia University and co-authors, we don’t know what they’ll look like.
The paper seeks to address this and concludes that wormholes, when viewed from high angles, would look like nothing we’ve ever seen. For small tilt angles, the authors believe the wormhole would exhibit a “very similar polarization pattern” to a black hole. Thus, M87*, seen at an estimated angle of 17 degrees, could be a wormhole and we wouldn’t know.
This does not mean that we are doomed to be unable to distinguish between wormholes and blacks. “More significant differences are observed for strongly lensed indirect images, where the intensity of polarization in wormhole spaces can grow to a level of an order of magnitude greater than that of a Schwarzschild black hole,” the authors wrote. The lens referred to here is not from a massive object between us and the hole that creates a gravitational lens. Instead, it is from The trajectories of photons are distorted by the hole’s massive gravitational field, causing them to complete a partial loop around the hole before heading toward us.
The situation is further complicated if we assume, as the authors did, that matter or light can pass in either direction through a wormhole. If this is the case, they speculate that “signals from the region beyond the throat are able to reach our world.” This will change the polarized image of the disk that we see around the hole, with light coming out from somewhere else having distinct polarization properties. This could provide what the authors call a “distinctive signature of detection of wormhole geometry.”
Besides the interest in finding wormholes to confirm their existence, and the fact that they might make interstellar travel possible, it’s nice to be able to tell them apart from black holes before getting too close. “If you were nearby, you would find out too late,” Nedkova told New Scientist. “You will know the difference when you die or pass.”
The authors acknowledge that their conclusions are drawn from a “simplified model of a magnetized liquid ring” orbiting the black hole. More advanced models may reveal differences that can be used to distinguish a wormhole from a black hole in other ways.
The paper has been published in Physical Review D.
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