The shape of the universe is one of the most important questions in cosmology, with far-reaching implications, up to and including the ultimate fate of the cosmos.
For decades, we've been measuring our universe to be geometrically flat, but a team of cosmologists are now reporting that our latest measurements actually prefer something rounder. But there's far more to the story than a simple measurement.
The surface of the Earth is curved. We know this because the tiles of geometry that you learned in high school don't always apply. For example, parallel lines don't always stay parallel on the Earth: lines of longitude intersect at the north and south poles, something that can never happen on a flat plain. And if you were to draw a triangle connecting three cities on the Earth, you would find that the angles inside that triangle add up to more than 180 degrees; again, good luck doing that on a flat plain.
Astronomers are very curious about the ultimate curvature of the universe: how do parallel lines and triangles behave on the very largest scales? They care because the shape of the universe is intimately connected to its fate. Einstein's theory of general relativity, which we use to understand the cosmos, tells us that the contents of space-time affect its shape, and the shape tells the contents how to move.
A geometrically flat universe will just keep on expanding forever, while a "closed" one will eventually pull back in on itself, leading to the reverse of the Big Bang, something called the Big Crunch.
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