Stephen Hawking explains how information can escape from black holes in his new theory

Stephen Hawking, the 74-year-old British theoretical physicist has created history again by saying that presence of black hole ‘hairs’ can be proved. He has published a paper titled “Soft Hair on Black Holes” outlining his theory that the solution to the paradox of Black Hole could be that “hairs” or light-induced holograms are left on the edge of the Black Hole, which support the information that goes into it. According to Hawking’s theory, the information lost or sucked into the Black Hole can be conserved.

Hawking shares the credit of writing this theory with Cambridge University’s Malcolm J Perry and Harvard’s Andrew Strominger. This new discovery may very well earn the scientists a Nobel Prize.

So, what is the black hole information paradox? According to Einstein’s general theory of relativity, the problem with black holes is that all information that crosses the boundary of a black hole – called the event horizon – is lost forever. Not even light is protected from this, that’s how black holes got their name.

However, Hawking challenged the assumption that anything sucked into the massive objects is lost forever. In particular, the theoretical physicist claimed to have discovered a mechanism ‘by which information is returned out of the black hole.’

His solution? “Hairs” (low or zero energy particles) that appear on the black hole’s event horizon that make a watermark of what has gone through it. The hairs shred information from particles falling into the holes in the same way that nose hair gathers dust.

As co-author Professor Andrew Strominger told Scientific American: “We show that when a particle goes in, it adds a soft photon to the black hole. So it adds hair to the black hole. And more generally if particle goes in – because all particles carry mass and are coupled to gravity – they always add a soft graviton. So there’s a kind of recording device.”

Hawking hinted at this last August in a lecture at the KTH Royal Institute of Technology in Sweden. “I propose that the information is stored not in the interior of the black hole as one might expect, but on its boundary, the event horizon,” explained Hawking. “The message of this lecture is that black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought. Things can get out of a black hole both on the outside and possibly come out in another universe.”

So when a black hole disappears, according to what Hawking proposes, information is lost forever, which is a problem, because quantum mechanics states that information can never be lost. Hence, the paradox.

“Going way back to Galileo or earlier, the idea of a physical law is that you start out with bodies in some state of motion and interacting, and you use the physical laws to determine either where they will be in the future or where they must have come from,” Harvard University physicist Andrew Strominger, a co-author of the study, told Scientific American. “So it’s a very big thing if black holes destroy information. It’s a very big thing to say that we cannot use physical laws in the way that we’ve been accustomed to for thousands of years to describe the world around us.”

Here’s where the new paper comes in. Staying true to Hawking’s previous assertion that “black holes ain’t as black as they are painted,” the new study adds another feature to these enigmatic bodies — the so-called “soft hairs.”

Hawking and his co-authors suggest that charged particles crossing the event horizon could leave traces of themselves in space-time in the form called soft photons and soft gravitons, which have no energy. These bizarre particles change the vacuum of space-time and allow it to preserve information about the original particles.

“We show that when a charged particle goes in, it adds a soft photon to the black hole. So it adds hair to the black hole. And more generally if any particle goes in — because all particles carry mass and are coupled to gravity — they always add a soft graviton,” Strominger said, in the interview with Scientific American. “So there’s a kind of recording device. These soft photons and gravitons record information about what went into the black hole — infinitely more information than we previously believed is recorded by this mechanism.”

The paper is published online for a kind of informal peer review and no one has yet reported a mistake in the calculations presented in the paper, but the theory is still believed to be incomplete. Sabine Hossenfelder of the Nordic Institute for Theoretical Physics wrote a blog post outlining her scepticism about it, in particular how black holes would transfer the held information into radiation once evaporated. “I am not at all convinced that the new idea proposed by Hawking, Perry, and Strominger solves the information loss problem,” she wrote, “but it seems an interesting avenue that is worth further exploration”.

As Perry admitted, he, Hawking, and Strominger are not 100 percent sure if this is the right answer to the black hole information paradox, but their paper is now out there for their peers to pick over everything and help them figure it out. “We’re saying that it’s a step on the way,” he concludes.