# Physicists may finally learn what's inside a black hole

While not the most eye-opening thought, the idea of holographic realities has seen applications outside of Elon Musk's Twitter feed — namely, in the use of quantum computing to explore a theory known as holographic duality.

It's an idea that suggests the theory of particles and gravity — while conventionally incompatible — are mathematically equivalent. Gravity describes things in three dimensions, where the two-dimensional fabric of spacetime curves or "bends" up or down to represent its force. But particle theory describes things in only two dimensions.

However, in cases of extreme gravitational force, like a black hole, holographic duality's aim of envisioning the universe as a holographic projection of particles could potentially reveal the interior of a black hole — as a projection of particles mapped on the curved fabric of spacetime.

And, a team of researchers analyzed holographic duality via quantum computing, in addition to deep learning, to discover quantum matrix models — the lowest energy state of mathematical problems surrounding the idea — bringing us one step closer to revealing the interior of black holes, according to a recent study published in the journal *PRX Quantum*.

And, for some scientists, this research could be a step toward expanding a holographic projection of particles into a quantum field of gravity — hinting at the world's first unified theory of everything.

That's a lot to hold your breath for, but worth trying.

## Quantum computing can help us solve particle theories

Enrico Rinaldi, a research scientist based in Tokyo, and hosted by the Theoretical Quantum Physics Laboratory within the Cluster for Pioneering Research, at RIKEN, in Wako, says in a press release this the research is edging closer to answering an eternal question.

"In Einstein's General Relativity theory, there are no particles — there's just space-time. And in the Standard Model of particle physics, there's no gravity, there are just particles. Connecting the two different theories is a longstanding issue in physics — something people have been trying to do since the last century."

If the scientists can solve this kind of quantum matrix model, they might uncover information about gravity

The study's quantum matrix models are sophisticated representations of particle theory. And, since holographic duality implies that gravitational theory and particle theory are mathematical equivalents, if the scientists can solve this kind of quantum matrix model, they might uncover information about gravity — which has remained an impenetrable black box for nearly a century.

In the study, Rinaldi and his colleagues employed two matrix models that could be solved via conventional procedures, but still retained key features of the more involved matrix models that describe black holes, via holographic duality.

"We hope that by understanding the properties of this particle theory through the numerical experiments, we understand something about gravity," says Rinaldi, who's also a research scientist at the University of Michigan's department of physics. "Unfortunately it's still not easy to solve the particle theories. And that's where the computers can help us."

## Unlocking a unified theory of physics

In essence, the matrix models are groups of numbers that represent objects in string theory — which consists of particles that exist as one-dimensional strings. By solving for matrix models that use these, the scientists look for a way to represent the system's lowest energy state called the "ground state". In this state, a system will retain its initial conditions until someone or something adds a force of some kind, to disrupt it.

"It's really important to understand what this ground state looks like because then you can create things from it," adds Rinaldi. "So for a material, knowing the ground state is like knowing, for example, if it's a conductor, or if it's a superconductor, or if it's really strong, or if it's weak. But finding this ground state among all the possible states is quite a difficult task. That's why we are using these numerical methods."

Ultimately, the researchers succeeded in discovering the ground state of both examined matrix models but emphasized the excessive cost of current quantum computing technology, and how more advances are needed to take their work to the next step: advancing a theory of quantum gravity via the notion of holographic duality.

**A light in the dark —** If quantum computers continue to advance, and perform more calculations for less steep costs, Rinaldi and his team might be able to reveal what happens inside of black holes, beyond the event horizon — a region immediately surrounding a black hole's singularity, within which not even light, nor perhaps time itself, can escape the immense force of gravity.

In practical terms, the event horizon prevents all conventional, light-based observations. But, and perhaps more compelling, the team hopes that further advances in this line of inquiry will do more than peek inside a black hole, and unlock what physicists have dreamed of since the days of Einstein: a unified theory of physics.