Quantum Paradox Reveals Universe's Single State

In 2019, theoretical physicists examining quantum gravity made a startling : their calculations showed that a closed universe like ours should contain only one possible quantum state. This single-state result meant the universe could be described without conveying even one bit of information - not the choice between zero and one, but no choice at all. The finding directly contradicted our observable reality, where stars, planets, and people demonstrate immense complexity. "We look around, and it certainly seems more complex than that," noted Rob Myers, a theoretical physicist at Perimeter Institute for Theoretical Physics in Waterloo, Canada, who was not directly involved in the research.

The paradox emerged from applying trusted mathematical formulas to understand quantum gravity. Physicists have good reason to trust these calculations because they build on fundamental physical ideas. Yet the math implied a universe with only one state, while our actual universe clearly contains far more. Now, a team of theorists has proposed an answer: the paradoxical result occurred because they sought an objective description of the state of the entire universe. Such a description might not be possible in principle because it implicitly assumes the universe exists without any observer to observe it.

The researchers built their work on holography, a concept developed almost 30 years ago by Juan Maldacena at the Institute for Advanced Study. Holography showed that difficult string theory calculations could sometimes be sidestepped by using familiar concepts from particle physics instead. This approach only works with anti-de Sitter geometry, which has a boundary often illustrated as resembling a tin can. Remarkably, everything that happens inside the can - including colliding particles and spinning black holes - is revealed in shadows on the can's outer surface. It's as if the 3D universe were equivalent to an image on a flat screen.

In 2019, Maldacena and three colleagues at IAS - Ahmed Almheiri, Raghu Mahajan, and Ying Zhao - used holographic thinking to better understand what happens inside black holes. Building on earlier work, they proposed a formula that tracks boundaries between regions within a black hole. This soon helped others uncover a potential explanation for a long-standing mystery: how black holes reveal information about what has fallen into them. Their success gave confidence that the formula was trustworthy for understanding gravity, and subsequent showed it held its own outside the original anti-de Sitter context.

When Maldacena applied the formula to our own universe, he uncovered something his colleagues found hard to accept: the region seemed almost completely empty. "I was pretty shocked by the argument," he said. It took a few years, but Zhao eventually found that the problem in Maldacena's calculation wasn't about mass or energy, but something more fundamental: information. When studying quantum theories, physicists need to keep track of each physical system's possible states using abstract mathematical spaces called Hilbert spaces. These spaces, named after early-20th-century mathematician David Hilbert, work by adding mathematical dimensions - the more dimensions, the more information the spaces can encode.

Most real quantum systems feature infinite-dimensional Hilbert spaces. Take a hydrogen atom: its electron can reach higher orbits when given energy, creating unlimited possibilities and thus an infinite-dimensional space. Physicists therefore expect the whole universe to have infinite states too. Yet when Maldacena applied his formula, he found instead just one dimension. There was no information to be found - the whole universe appeared to contain everything in only one state. It lacked complexity entirely. "On my desk there are infinite states," noted Edgar Shaghoulian at University of California, Santa Cruz, highlighting the paradox.

As physicists continued studying different types of universes, they kept seeing the same pattern. While the IAS group considered our universe, Henry Maxfield at Stanford University and collaborator Donald Marolf looked at hypothetical bubbles of space-time called baby universes. They found the same stark simplicity. Increasingly, the barrenness of these universes appeared to be a universal trend. The situation presents a clear paradox: calculations consistently imply any closed universe has only one state, while our universe may well be closed yet appears infinitely complex.

In 2023, Shaghoulian noted that physicists had seen this strange behavior before in topological theories. Mathematicians use these theories to chart the shape, or topology, of geometric spaces. Topological theories also feature one-dimensional Hilbert spaces. When you split up geometric spaces into multiple zones, you need to describe the many possible ways they can connect. To track these possibilities, you need a bigger Hilbert space. Shaghoulian proposed physicists might do something similar by splitting up the universe: bring in an observer.

Ying Zhao, now a theoretical physicist at Massachusetts Institute of Technology, was part of the team that devised a solution to the one-state problem. Quantum mechanics requires a distinction between observer and observed - such as a scientist carrying out an experiment and the system they observe. The observer tends to be something small in quantum mechanics, like an atom. When the observer becomes big and far away, they're well described by classical physics. Shaghoulian observed this split was analogous to the kind that enlarges topological Hilbert spaces.

In 2024, Zhao began working on the problem of how to put an observer into the universe. She and her colleagues Daniel Harlow and Mykhaylo Usatyuk thought about the observer as introducing a kind of boundary: not the edge of the universe, but the boundary of the observer themself. When you consider a classical observer, the Hilbert space returns to having many dimensions, her collaborators showed. The MIT team's work came at the beginning of 2025, around the same time another group came forward with a similar idea. Others chimed in to point out connections to earlier work.

At this stage, everyone involved emphasizes they don't know the full solution. The paradox itself may represent a misunderstanding that evaporates with a new argument. So far, adding observers and trying to account for their presence may be the safest path forward. "Am I really confident to say this is the right thing that solves the problem? I cannot say that. We try our best," Zhao said. If the idea holds up, using subjective accounts could represent a paradigm shift in physics. Physicists typically seek a "view from nowhere" - a stand-alone description of nature. They want to know how the world works, with observers like us emerging as parts of that world. If physicists come to understand the universe in terms of private boundaries for private observers, the view from nowhere becomes less viable. Perhaps views from somewhere are all we can ever have.