For the better part of a century, quantum physics and general relativity have been a marriage on the rocks. Each perfect in their own way, they just can’t stand each other when they are in the same room.
Now a mathematical proof of the quantum nature of black holes might just show us how the two can be reconciled, at least enough to create a grand new theory of how the Universe works on cosmic and microcosmic scales.
A team of physicists has mathematically demonstrated a curious quirk of how these extremely dense objects can exist in a state of quantum superposition while occupying a range of possible properties.
Their calculations showed that mass superpositions in a theoretical type of black hole called a BTZ black hole occupy surprisingly different mass bands at the same time.
Typically, any garden-variety particle can exist in a superposition of states, with features such as spin or momentum determined only after they become part of an observation.
Where some properties, such as charge, only come 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 measures over others in a pattern that could be useful for modeling the mass in a quantized way. This could give us a new framework for probing the quantum-gravitational effects of superimposed black holes in order to ease the tension between general relativity and quantum theory.
“Until now, we haven’t investigated in depth whether black holes exhibit some of the weird and wonderful behaviors of quantum physics,” explains theoretical physicist Joshua Fu from the University of Queensland in Australia.
“One such behavior is superposition, where quantum-scale particles can exist in multiple states at once. This is most often illustrated by Schrödinger’s cat, which can be dead and alive at the same time.”
“But, for black holes, we wanted to see if they could have very different masses at the same time, and it turns out they do. Imagine you’re both wide and tall, as well as short and thin at the same time – It’s a confusing situation intuitively, as we’re anchored in the world of traditional physics. But this is the reality for quantum black holes.”
The extreme gravity surrounding black holes is an excellent laboratory for detection quantum gravity – the rolling spacetime continuum according to the general theory of relativity associated with quantum mechanical theory, which describes the physical Universe in terms of discrete sizes, such as particles.
Models based on certain types of black hole could simply lead to a single theory that could explain particles and gravity. Some of the phenomena observed around a black hole cannot be described in general relativity, for example. For that, we need quantum gravity – a unified theory that incorporates both sets of rules and somehow makes them play nice.
So Foo and his colleagues developed a mathematical framework that allows physicists to observe a particle outside a black hole that is in a quantum superposition state.
Mass was the main property they investigated, 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 a fundamental contribution to the foundation of black hole thermodynamics – were on the money,” says quantum physicist Magdalena Zych of the University of Queensland.
“[Bekenstein] he hypothesized that black holes can only have masses of certain values, meaning they must fall within certain bands or ratios – this is how the energy levels of an atom work, for example. Our modeling showed that these superimposed masses were, in fact, in certain defined zones or ratios – as predicted by Bekenstein.
“We didn’t assume there was such a pattern, so the fact that we found this evidence was quite surprising.”
The results, the researchers say, provide a path for future investigation of quantum gravity concepts such as quantum black holes and superimposed spacetime. In order to develop a complete description of quantum gravity, the inclusion of these concepts is crucial.
Their research also allows for a more detailed investigation of this superimposed spacetime and the effects it has on the particles within it.
“The Universe is always revealing itself to us to be more strange, mysterious and fascinating than most of us could ever imagine,” says Zych.
The research has been published in Physical Review Letters.