A team of scientists have suggested a possible solution to the famously tricky black hole information loss paradox, first proposed by Professor Stephen Hawking nearly 50 years ago.

Black holes are strange objects which (though we have learned plenty about them) confound our understanding of physics. Formed when massive stars collapse, black holes are areas of space where gravity is so strong that not even light can escape. Their existence posed a problem when studying them in terms of thermodynamics. The final state of a black hole, when it reaches equilibrium, is dependent only on three parameters: its mass, angular momentum, and electric charge.

“In classical general relativity, a black hole prevents any particle or form of radiation from escaping from its cosmic prison,” French astrophysicist Jean-Pierre Luminet explains in a 2016 review. “For an external observer, when a material body crosses an event horizon all knowledge of its material properties is lost. Only the new values of M [mass], J [angular momentum], and Q [electric charge] remain. As a result, a black hole swallows an enormous amount of information.” 

Sounds simple doesn’t it, or at least as simple as physics can get? But if a black hole has mass (and they have a lot of it) then they should have a temperature according to the first law of thermodynamics, and in line with the second law of thermodynamics, they should radiate heat. Stephen Hawking showed that black holes should emit radiation – now termed Hawking radiation – formed at a black hole’s boundary.

“Hawking then pointed to a paradox. If a black hole can evaporate, a portion of the information it contains is lost forever,” Luminet continued. “The information contained in thermal radiation emitted by a black hole is degraded; it does not recapitulate information about matter previously swallowed by the black hole. The irretrievable loss of information conflicts with one of the basic postulates of quantum mechanics. According to the Schrödinger equation, physical systems that change over time cannot create or destroy information, a property known as unitarity.”

This is known as the black hole information paradox, and – given how it appears to violate our current understanding of the universe – it has been the subject of a lot of study and debate. Proposed solutions are that black holes could have a firewall, are a little fuzzy, or that black holes are actually gravastars rather than what we think of as a black hole.

One area of focus has been what happens to entangled particles that fall into a black hole. Quantum mechanics tells us that measurement of one entangled particle can give us information about its entangled partner, and it has been suggested that this non-locality could provide a solution.

“Giddings proposed that the information which fell into the BH can escape it via non-violent non-locality (NVNL), a non-local interaction between the inside and the outside of the BH, with associated nonviolent space-time fluctuations from this information transfer,” the team explain in their new paper, which has been posted as a preprint and has not yet been peer-reviewed. 

“In contrast to firewalls, these quantum fluctuations would be spread out over a larger distance range – up to a Schwarzschild radius away.”

If this is the case, and information really does escape from a black hole due to non-locality, the team suggests we should be able to detect it in gravitational waves, with the waves carrying information from what fell into the black hole rather than random noise.

“We find that the waveform exhibits random deviations which are particularly important in the late inspiral-plunge phase. We find an optimal dephasing parameter for detecting this effect with a principal component analysis,” the team writes. “This is particularly intriguing because it predicts random phase deviations across different gravitational wave events, providing theoretical support for hierarchical tests of general relativity.”

It’s a neat idea, and one that the team believes could be tested by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo Gravitational Wave Interferometer (Virgo) networks, or next-generation gravitational wave detectors. While interesting, the team has more work to do, including modeling “the effect of NVNL perturbations on wave propagation through the final [black hole’s] spacetime in order to capture how the ringdown waves will be modified”, and factoring in black hole spin. Detection of such waves could take a lot longer still.

The study is posted to preprint server arXiv.