Scientists Say They’ve Finally Solved Stephen Hawking’s Black Hole Paradox

SCIENCE, 8 May 2023

Jackie Appel | Popular Mechanics - TRANSCEND Media Service

Andriy Onufriyenko//Getty Images

  • Scientists may have just solved the famous Hawking information paradox.
  • The paradox states that information can neither be emitted from a black hole or preserved inside forever. But the laws of quantum physics dictate that information cannot be destroyed.
  • By adding quantum gravity into Hawking’s original calculations, researchers found that information could in fact be carried out on Hawking radiation.

5 May 2023 – Black holes are one of the most active areas of cosmological research. We know they’re a big deal, we know their effects reach into the far edges of the universe, and we know they really test the laws of physics from time to time.

Interestingly, despite these huge gravity wells continuing to prove somewhat of a mystery, they’ve long been thought pretty easy to describe. Researchers only needed three parameters—their mass, their angular momentum (how fast they’re spinning), and their electric charge. This straightforward-ness has led some physicists to refer to black holes as “bald.”

But there’s a catch, and it’s a pretty big one—the Hawking information paradox. Introduced by Stephen Hawking in 1976, this paradox basically says that black holes are doing something impossible: they’re destroying information.

Astronomers, however, think they’ve finally cracked that paradox.

According to the laws of quantum physics, information cannot be destroyed. You should be able to analyze an existing object and use the information contained within to track that object back through its evolutionary history to see where it came from. For example, you should be able to look at the aftermath of a supernova and tell what kind of star exploded.

Hawking argued, though, that under our current understanding of black holes, you can’t track them back to their source. You can’t look at the radiation of a black hole and see what kinds of stars have fallen in. This is because the radiation leaking out of black holes (known as Hawking radiation) is thermal, which can’t carry information.

Hawking also discovered that the information can’t stay locked in the black hole forever. And if it can’t stay in and it can’t ride radiation out, it’s being destroyed.

Or is it?

According to a group of researchers who just published a new study, the answer is no. And it comes back to the idea of “bald” black holes.

Last year, this group of researchers published a paper that claimed that black holes weren’t bald at all, but had what is now casually referred to as “quantum hair.” It’s basically the idea that if you look at the way black holes warp spacetime right at their horizons, you can detect a sort of fingerprint in the quantum realm pointing to where the matter within came from. Essentially, the hair contained the missing information.

At the time of that paper’s release, the whole idea of quantum hair was nothing more than a deeply abstract mathematical concept. But now, in their new research, the team argues that the hair is the whole ball of wax when it comes to cracking open the paradox.

The researchers re-ran Hawking’s original calculations that showed that the only thing coming out of black holes was information-less thermal Hawking radiation, but with one added ingredient—quantum gravity. That’s the description of gravity as it exists in the quantum realm, and it’s something Hawking didn’t originally take into account.

“While these quantum gravitational corrections are minuscule, they are crucial for black hole evaporation,” Xavier Calmet, professor of physics and lead author on the study, said in a Live Science article. “We were able to show that these effects modify Hawking radiation in such a way that this radiation becomes non-thermal. In other words, factoring in quantum gravity, the radiation can contain information.”

The study shows that Hawking radiation, contrary to historical belief, could scoop up information from the black holes and carry it out into the universe. Information that had been stored in the hairs around black holes could be carried out. No more destruction, no more paradox.

Even though this group is now sure they’ve solved what Hawking could not, it’s going to be very difficult—if not impossible—to observationally confirm the findings. That’s not at all to say they should be dismissed, of course. We’ve learned a lot about the universe from math and models, even though we’ve never seen certain objects.

It just means we can’t see this radiating information with our own instruments. Hawking radiation is extremely weak (and itself currently entirely theoretical), and we don’t have any detectors strong enough to pick it up. We may eventually be able to see the quantum hair using gravitational waves, but even that tech is still firmly next-gen.

For now, we’ll have to settle for what we can figure out on Earth. The team has already produced intense mathematical models of this phenomenon, and they suggest it could be tested in lab-housed simulated black holes.

There are still plenty of avenues for exploration and deeper study. And if this study has reinforced anything, just because information isn’t obvious, doesn’t mean it doesn’t exist.


Jackie Appel is a writer and Associate News Editor from Pennsylvania. She’s especially fond of writing about space and physics, and loves sharing the weird wonders of the universe with anyone who wants to listen. She is supervised in her home office by her two cats.


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