Wormholes Could Explain What Happens to Matter Swallowed by Black Holes

Physicists may have discovered what happens to matter that is swallowed by black holes by considering wormholes, theoretical bridges that connect distant points in the Universe.

The team from Japan's RIKEN research institute, including RIKEN Interdisciplinary Theoretical and Mathematical Sciences researcher Kanato Goto, show that black holes mimic wormholes—a concept very familiar to science fiction fans—allowing an escape tunnel back into the Universe for information trapped at their heart.

Goto said in a press release from RIKEN: "A wormhole connects the interior of the black hole and the radiation outside, like a bridge."

The model suggested by Goto and his colleagues could solve a long-standing paradox surrounding what happens to pure information stored in black holes if they "evaporate" as predicted by Stephen Hawking in the 1970s.

Do Black Holes Evaporate?

According to Einstein's theory of general relativity, from which the concept of the singularity at the heart of a black hole first arose, nothing that falls into a black hole should be able to escape. The gravitational influence of a black hole is so strong that even light that passes beyond what is known as the event horizon of a black hole isn't fast enough to escape.

All matter that passes this point makes its way inexplicably to the singularity at the heart of the black hole, the point at which conventional physics break down, and is destroyed. The physical information of this matter should remain there in that singularity in perpetuity, however.

That concept was challenged in the 1970s when British physicist Hawking suggested that black holes should "leak" radiation. Something which would later be named "Hawking radiation."

The emission of Hawking radiation causes black holes to "evaporate" and would mean their last moments are marked by an explosion, though for larger black holes this would happen on a timescale longer than the lifetime of the Universe.

Goto said: "This is called black hole evaporation because the black hole shrinks, just like an evaporating water droplet."

This leads to a paradox as this evaporation should include information about the matter. But this contradicts quantum physics which says that information like this can't disappear from the Universe.

Goto said: "This suggests that general relativity and quantum mechanics as they currently stand are inconsistent with each other. We have to find a unified framework for quantum gravity."

Solving the Black Hole Paradox

As a solution to this problem, known as the black hole paradox, physicists have investigated the idea that information could escape from black holes encoded in Hawking radiation. The problem with this solution involves entropy—a measure of the energy of a system that is unavailable to do useful work.

In the 1990s, physicist Don Page theorized that if information is saved then entropy will build in the system, as predicted by the theory of thermodynamics, but drops to zero when the black hole has fully evaporated.

This work removes problems associated with the solution, suggesting that physicists are right to suspect that information is preserved even after the black hole's demise.

As general relativity suggests that black holes are actually areas in spacetime with extremely curved geometry, often compared to a bowling ball placed on a stretched rubber sheet, the team's computations also involved looking at the extreme geometry of these regions.

"We discovered a new spacetime geometry with a wormhole-like structure that had been overlooked in conventional computations. Entropy computed using this new geometry gives a completely different resul," Goto said.

Goto concedes that what is missing from the team's model is an explanation of how Hawking radiation is able to carry information away from a black hole. Solving this, the RIKEN researcher believes, may hinge on solving a long-standing problem is physics, uniting two of its most successful theories, general relativity and quantum mechanics.

Goto concludes: "We still don't know the basic mechanism of how information is carried away by the radiation. We need a theory of quantum gravity."

Black hole
An illustration of a black hole consuming dust and gas. Researchers have used the idea of wormholes to explain what could happen to matter that passes into the center of a black hole. vchal/GETTY