Superconductors may shed light on the black hole information paradox

Scientists are trying to understand what happens to information that falls into a black hole

illustration of a black hole

MIRROR, MIRROR When black holes evaporate, where does the trapped information go? One potential explanation, that the black hole (illustrated) reflects the information instead of trapping it, has parallels with the behavior of materials that conduct electricity without resistance.

NASA Goddard Space Flight Center

LOS ANGELES ­— Insights into a black hole paradox may come from a down-to-Earth source.

Superconductors, materials through which electrons can move freely without resistance, may share some of the physics of black holes, physicist Sreenath Kizhakkumpurath Manikandan of the University of Rochester in New York reported March 7 at a meeting of the American Physical Society. The analogy between the two objects could help scientists understand what happens to information that gets swallowed up in a black hole’s abyss.

When a black hole gobbles up particles, information about the particles’ properties is seemingly trapped inside. According to quantum mechanics, such information cannot be destroyed. Physicist Stephen Hawking determined in 1974 that black holes slowly evaporate over time, emitting what’s known as Hawking radiation before eventually disappearing. That fact implies a conundrum known as the black hole information paradox (SN: 5/31/14, p. 16): When the black hole evaporates, where does the information go?

One possible solution, proposed in 2007 by physicists Patrick Hayden of Stanford University and John Preskill of Caltech, is that the black hole could act like a mirror, with information about infalling particles being reflected outward, imprinted in the Hawking radiation. Now, Manikandan and physicist Andrew Jordan, also of the University of Rochester, report that a process that occurs at the interface between a metal and a superconductor is analogous to the proposed black hole mirror.

The effect, known as Andreev reflection, occurs when electrons traveling through a metal meet a superconductor. The incoming electron carries a quantum property known as spin, similar to the spinning of a top. The direction of that spin is a kind of quantum information. When the incoming electron meets the superconductor, it pairs up with another electron in the material to form a duo known as a Cooper pair. Those pairings allow electrons to glide easily through the material, facilitating its superconductivity. As the original electron picks up its partner, it also leaves behind a sort of electron alter ego reflecting its information back into the metal. That reflected entity is referred to as a “hole,” a disturbance in a material that occurs when an electron is missing. That hole moves through the metal as if it were a particle, carrying the information contained in the original particle’s spin.

Likewise, if black holes act like information mirrors, as Hayden and Preskill suggested, a particle falling into a black hole would be followed by an antiparticle coming out — a partner with the opposite electric charge — which would carry the information contained in the spin of the original particle. Manikandan and Jordan showed that the two processes were mathematically equivalent.

It’s still not clear whether the black hole mirror is the correct solution to the paradox, but the analogy suggests experiments with superconductors could clarify what happens to the information, Jordan says. “That’s something you can’t ever do with black holes: You can’t do those detailed experiments because they’re off in the middle of some galaxy somewhere.”  

The theory is “intriguing,” says physicist Justin Dressel of Chapman University in Orange, Calif. Such comparisons are useful in allowing scientists to take insights from one area and apply them elsewhere. But additional work is necessary to determine how strong an analogy this is, Dressel says. “You may find with further inspection the details are different.”

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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