Schrödinger’s cat: Simulations show black holes exhibit baffling quantum behavior

Black holes can be massive and small, dead and alive all at the same time, just like Schrödinger’s cat.
Chris Young
An artist's impression of a black hole.
An artist's impression of a black hole.

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A group of physicists conducted a study on black holes that arguably poses more questions than it answers.

The scientists, from the University of Queensland, confirmed a number of bizarre quantum properties of the cosmic giants, including their ability to have different masses at the same time, a press statement reveals.

Their study links the mysterious behavior of black holes to the weird and wonderful world of quantum physics, shedding new light at the same time as highlighting the elusive behavior of the colossal objects.

Simulating the quantum properties of black holes

The findings, published in a new study in the journal Physical Review Letters, show that black holes have properties typical of quantum particles, meaning they can hold a number of states at the same time, much like the famous thought experiment Schrödinger’s cat. The scientists used computer modeling to link the mysterious properties of black holes to the principles of quantum physics, which explain the behavior and quirks of subatomic particles.

"Black holes are an incredibly unique and fascinating feature of our universe," study lead Joshua Foo, a Ph.D. candidate at the University of Queensland, explained.

"They’re created when gravity squeezes a vast amount of matter incredibly densely into a tiny space, creating so much gravitational pull that even light cannot escape," he continued. "It’s a phenomenon that can be triggered by a dying star. But, until now, we haven’t deeply investigated whether black holes display some of the weird and wonderful behaviors of quantum physics."

One example of this behavior is superposition, where subatomic particles can exist in multiple states at the same time. The scientists devised a mathematical framework that simulated a scenario in which a quantum particle sat just outside a massive black hole.

"For black holes," Foo said, "we wanted to see whether they could have wildly different masses at the same time, and it turns out they do. Imagine you’re both broad and tall, as well as short and skinny at the same time — it's a situation which is intuitively confusing since we’re anchored in the world of traditional physics. But this is reality for quantum black holes."

Slowly uncovering the great black hole mystery

American-Israeli theoretical physicist Jacob Bekenstein was the first to theorize that black holes may have quantum properties. Now, the University of Queensland scientists say their new findings confirm some of Bekenstein's predictions.

"Our modeling showed that these superposed masses were, in fact, in certain determined bands or ratios — as predicted by Bekenstein," study co-author Magdalena Zych explained. "We didn't assume any such pattern going in, so the fact we found this evidence was quite surprising."

Though recent advances, such as the Event Horizon Telescope images of two black holes, add to our knowledge of black holes, we're far from understanding the inner workings of black holes. The new study lends weight to sci-fi depictions of the cosmic giants as colossal gateways that warp space and time in completely unexpected ways.


We present a new operational framework for studying “superpositions of spacetimes,” which are of fundamental interest in the development of a theory of quantum gravity. Our approach capitalizes on nonlocal correlations in curved spacetime quantum field theory, allowing us to formulate a metric for spacetime superpositions as well as characterizing the coupling of particle detectors to a quantum field. We apply our approach to analyze the dynamics of a detector (using the Unruh-deWitt model) in a spacetime generated by a Banados-Teitelboim-Zanelli black hole in a superposition of masses. We find that the detector exhibits signatures of quantum-gravitational effects corroborating and extending Bekenstein’s seminal conjecture concerning the quantized mass spectrum of black holes in quantum gravity. Crucially, this result follows directly from our approach, without any additional assumptions about the black hole mass properties.

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