The cosmos may have something in common with a doughnut.

In addition to their fried, sugary goodness, doughnuts are known for their shape, or in mathematical terms, their topology. In a universe with an analogous, complex topology, you could travel across the cosmos and end up back where you started. Such a cosmos hasn’t yet been ruled out, physicists report in the April 26 Physical Review Letters

On a shape with boring, or trivial topology, any closed path you draw can be shrunk down to a point. For example, consider traveling around Earth. If you were to go all the way around the equator, that’s a closed loop, but you could squish that down by shifting your trip up to the North Pole. But the surface of a doughnut has complex, or nontrivial, topology (SN: 10/4/16). A loop that encircles the doughnut’s hole, for example, can’t be shrunk down, because the hole limits how far you can squish it. 

The universe is generally believed to have trivial topology. But that’s not known for certain, the researchers argue.

“I find it fascinating … the possibility that the universe might have nontrivial or different types of topologies, and then especially the fact that we think we might be able to measure it,” says cosmologist Dragan Huterer of the University of Michigan in Ann Arbor, who was not involved with the study.

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