Astronomy’s decades-long quest to understand cosmic topology

If some aspects of cosmic topology turn out to be true, the idea that starships might voyage across the cosmos for hundreds of thousands of light-years without ever returning to the same neck of spacetime could be problematic.

That’s because some aspects of cosmic topology (the global shape and connectivity of our cosmos) could dictate a closed-loop universe—at least on the largest scales. That means that, in some instances, if a starship heads in one direction long enough, hypothetically, it could return to its starting point.

“In some cases, there is an actual physical and straight path that can take you back to where you started, but not to when you started,” Andrew Jaffe, professor of cosmology and astrophysics at Imperial College London, told me via email. “If it took you back to the original time and spatial point, you would have something called a ‘closed timeline curve’—also known as a time machine,” he says.

The current paradigm is that we live in a flat cosmos that is infinite in all directions. But global topology may ultimately invalidate part or all of that axiom.

But topology is characterized by the possible existence and properties of nonshrinkable closed loops—if you could travel far enough in some direction along the loop, you would return to your starting point, note the authors of a 2026 paper in the journal Nature Astronomy.

The goal of astrophysicists like Jaffe is to identify the signatures of such topology via large-scale cosmological observations.

Cosmic topology would imprint subtle signatures on the cosmic microwave background (CMB) and on the three-dimensional distribution of matter, potentially breaking homogeneity at the largest scales, the authors write.

The CMB is the earliest cosmic light currently observable. It represents the light that last interacted with matter some 380,000 years after the Big Bang.

Cosmologists have been observing the CMB since the 1960s, but only since the early 2000s have they had enough sensitivity to detect the patterns that would enable them to see topology.

Patterns beyond the CMB

“The modern era of cosmic topology started in the late 1990s when we realized we could use patterns in the CMB to look for topology,” Jaffe, author of the 2025 book “The Random Universe: How Models and Probability Help Us Make Sense of the Cosmos,” told me. “There were great strides with data from the WMAP satellite in the mid-2000s and then with yet higher-quality data in the 2010s,” he says.

The data has not improved much since then.

But in the last few years, Jaffe and colleagues have created a group called COMPACT (Collaboration for Observations, Models and Predictions of Anomalies and Cosmic Topology), now comprising about 20 international scientists dedicated to thinking about this topological problem.

“Our work with COMPACT has started to put these results into the full mathematical theory and details of the possible topologies that could describe our universe,” Jaffe says.

A true three-dimensional map of the observable cosmos would go a long way in identifying cosmic topology, beyond just studying anomalies on the surface of the cosmic microwave background. In other words, it would map the gas, galaxies and clusters of galaxies that astronomers can observe with the best telescopes.

“A proper three-dimensional map of that matter would give us even more information about the topology of the universe—possibly all the information that we could ever have,” Jaffe says.

The goal is to try to see those repeating patterns by looking at as much of the universe as possible.

As for what would be a telltale signature of cosmic topology?

“The existence of such ‘identifications’ means that two areas of the sky that seem to be far apart might in fact be close together,” Jaffe says. “In the simplest case, this gives us repeated patterns: For the CMB, it might mean that there is a circle on one side of the sky that has exactly the same pattern as a circle far away from it,” he says.

Jaffe uses the analogy of a three-dimensional torus, a three-dimensional geometric shape that resembles a ring or a doughnut.

“Imagine a circle that goes around the ‘tube’ of a doughnut that would cut through the tube,” Jaffe says. “The existence of paths like this indicates the kind of topology we are looking for,” he says.

Topological galaxy clusters

There might even be signatures of topology in galaxy clusters that mirror each other from halfway across the cosmos. But such phenomena will be difficult to observe.

“Because we know that the scale of the topology, if it is something like a torus, must be large enough that we can’t observe those twins,” Jaffe says. “They are too far away from each other, and from us, to see both at once,” he says.

And even if we can eventually observe the cosmos on such large scales, this type of topological phenomenon may forever be out of our reach.

Cosmological fortune

We may also be fortunate, and the evidence for cosmic topology may be sitting in existing data, the authors write. Or it may be collected over the coming years in campaigns to observe the CMB and map the distribution and velocities of galaxies and other tracers of large-scale structure, they note.

The bottom line?

“We need to know the universe’s size: If it’s too big—much larger than the distance to the CMB sphere—we won’t be able to detect it,” Jaffe says.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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