Black holes in quantum states have surprisingly strange masses

For nearly a century, quantum physics and general relativity have been a marriage on hold. Each perfect in their own way, these two just can’t stand each other in the same room.

Now, mathematical proof of the quantum nature of black holes might just show us how the two can reconcile, at least enough to develop a grand new theory about how the universe works on the cosmic and microcosmic scales.

A team of physicists has mathematically demonstrated a curious way in which these amazingly dense objects could exist in a state of quantum superposition while simultaneously assuming a spectrum of possible properties.

Their calculations showed that the mass superpositions in a theoretical type of black hole called the BTZ black hole occupy surprisingly different mass bands simultaneously.

Normally, any garden-like particle can exist in a superposition of states, with properties such as spin or momentum only being determined once they have become part of an observation.

While some properties, like charge, only exist in discrete units, mass is usually not quantized, meaning that the mass of an unobserved particle can be anywhere within a range of maybe.

However, as this research shows, the superposition of masses held by a black hole tends to favor some masses over others in a pattern that could be useful for quantized mass modeling. This could give us a new framework to study the quantum gravitational effects of superimposed black holes, to ease the tension between general relativity and quantum theory.

“Until now, we haven’t thoroughly investigated whether black holes exhibit some of the weird and wonderful behaviors of quantum physics,” explains theoretical physicist Joshua Foo of the University of Queensland in Australia.

“One such behavior is superposition, where particles can exist in multiple states at the same time on a quantum scale. This is most often illustrated by Schrödinger’s cat, which can be dead and alive at the same time.”

“But with black holes, we wanted to see if they could have very different masses at the same time, and it turns out they do. Imagine being tall and tall and short and thin at the same time – it’s a situation that is intuitively confusing as we are anchored in the world of traditional physics. But that’s the reality for quantum black holes.”

The extreme gravity surrounding black holes is an excellent laboratory for probing quantum gravity – the rolling continuum of spacetime according to general relativity combined with quantum mechanical theory, which describes the physical universe in terms of discrete entities such as particles.

Models based on certain types of black holes could lead to a single theory that could explain particles and gravity. For example, some of the effects observed around a black hole cannot be described using general relativity. For that we need quantum gravity – a unified theory that takes both sets of rules and somehow makes them play well.

So Foo and his colleagues developed a mathematical framework that effectively allows physicists to observe a particle outside a black hole that is in a state of quantum superposition.

Mass was the most important property they studied, since mass is one of the only properties of black holes that we can measure.

“Our work shows that the very early theories of Jacob Bekenstein – an American and Israeli theoretical physicist who made fundamental contributions to the foundation of black hole thermodynamics – were on the money,” says quantum physicist Magdalena Zych of the University of Queensland.

“[Bekenstein] postulated that black holes can only have masses that have certain values, meaning they must fall within certain bands or ratios — that’s how the energy level of an atom works, for example. Our modeling showed that these superimposed masses were indeed in certain fixed bands or ratios – as predicted by Bekenstein.

“We didn’t think such a pattern would occur, so the fact that we found this evidence was quite surprising.”

The results, the researchers say, provide a path for future study of quantum gravity concepts such as quantum black holes and superimposed spacetime. In order to develop a complete description of quantum gravity, the incorporation of these concepts is crucial.

Her research also allows for a more detailed study of this superimposed spacetime and the effects it has on particles within it.

“The universe reveals to us that it is always stranger, more mysterious and more fascinating than most of us could have ever imagined,” says Zych.

The research was published in Physical Verification Letters.