There are few places in the universe that invite as much curiosity—and terror—as the interior of a black hole. These extreme objects exert such a powerful gravitational pull that not even light can escape them, a feature that has left many properties of black holes unexplained.
Now, a team led by Enrico Rinaldi, a research scientist at the University of Michigan, have used quantum computing and deep learning to probe the bizarre innards of black holes under the framework of a mind-boggling idea called holographic duality. This idea posits that black holes, or even the universe itself, might be holograms.
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“The new techniques do not directly investigate the idea of the universe as a holographic projection,” Rinaldi said in an email. “If a black hole can be described by the holographic duality, then we believe that the gravity in our entire universe could be also described by holography.”
“However, this last step is still under intense research and it is not directly related to the techniques we presented,” he noted. “Our techniques make difficult computations possible and provide tools to test the idea that the universe is a hologram in the future.”
To that point, Rinaldi and his colleagues employ so-called “matrix models” to examine the mysterious behavior of gravity at quantum scales, known as quantum gravity. The researchers believe that these computational techniques could become “the new Swiss army knife” of quantum gravity studies, according to a recent study published in the peer-reviewed journal PRX Quantum.
The new research is the latest iteration of a decades-long effort to square the laws of physics on cosmic and quantum scales. In the expansive realm of stars and galaxies, reality is governed by Einstein’s theory of general relativity, while in the tiny world of atoms and particles, objects move according to the bizarre principles of quantum mechanics. Since these two systems don’t neatly cohere, researchers across many fields have been searching for some way to combine them into a unified field theory that could explain the universe on both small and large scales.
Quantum gravity is at the center of many of these discussions, since nobody knows how gravity works in the quantum realm. Black holes have become natural laboratories for developing theories about quantum gravity, because general relativity cannot explain predictions of gravitational phenomena near these massive objects.
“Black holes are mysterious objects where our theories of general relativity and quantum mechanics clash with each other,” said Rinaldi. “Researchers, including Albert Einstein and Steven Hawking in the past, are studying black holes in the hope to realize a theory of gravity consistent with the rules of quantum mechanics, called quantum gravity.”
“It is believed that such a theory would be able to explain what happens to particles when they enter a black hole and how information transforms when in the proximity of a black hole (or a wormhole),” he continued. “A more ambitious goal is to understand how the bending of space and time near a black hole emerges mathematically from more fundamental objects such as strings and particles (as in string theory).”
One particularly trippy outgrowth of this research is the idea that black holes are two-dimensional holographic projections of three-dimensional objects. In other words, black holes could be optical illusions analogous to holograms that produce a 3D image from a 2D surface. This is a useful way to think about black holes in part because subtracting a dimension simplifies attempts to make gravity fit into quantum field theory. What’s more, it also raises the wild possibility that our entire universe, likewise, exists in two dimensions as a holographic projection of a three-dimensional space.
While the new study does not investigate the idea that the universe is a hologram, Rinaldi’s team ran matrix models to test the limits of a concept known as ”holographic duality” that can create new links between general relativity and quantum mechanics. The team was able to model the lowest-energy state of particles in a numerical system, called a ground state, which essentially establishes a stable baseline for future studies that involve more properties of the system, such as the configuration of particles at a ground state around black holes.
“The ground state is the configuration of a system with the minimal energy,” Rinaldi said. “Other standard techniques can find this energy without knowing what the configuration is, while it is important to also know the configuration itself in order to study other properties besides the energy.”
“We focus on the energy because the new techniques we employ have to be benchmarked on known results before they can be used for the next steps of the research program,” he continued. “This is why the energy is important in our study. Bear in mind that the most important aspect going forward will not be the energy, but the configuration of the ground state because it will encode information about space time.”
In this way, the new research advances techniques to explore black holes and the universe itself. The achievement “is a very promising outcome, which is demonstrated here for the first time,” according to the study. Rinaldi and his colleagues plan to build on their findings by developing even more complex models that will better simulate phenomena found in real experiments and nature.
“I am interested in taking the quantum algorithms and machine learning models to the next level, for example by studying how they behave under different, more realistic, settings (we only studied two examples, and both were done under ‘ideal’ conditions in our pioneering work),” Rinaldi said.
“One example is to use existing quantum computers to provide results for the ground state that we are interested in: contrary to what we did in the paper, where we emulated an ideal quantum algorithm, a real quantum hardware is affected by ‘noise’ which affects the final answer,” he continued. “We need to understand how much the answer is affected and find the best techniques to mitigate these potential errors.”
While it’s not yet possible to literally peek inside a black hole, the study opens new mathematical windows into these fascinating objects and the unknown physics that governs them.
