Is the Universe Not Quite Flat? express
Light from distant stars travels for billions of years, and during that time space itself stretches. How can we check whether it stays as flat as a sheet of paper or bends like a saddle? Astronomers gathered data on supernova explosions, such flashes are visible from enormous distances and act as beacons. They added a map of galaxy positions from the recent DESI survey. Then they applied a clever trick: instead of assuming the Universe is flat from the start, they let the data reveal the shape on its own.
The result is intriguing. When the scientists allowed space to be curved, the data slightly favored a not-perfectly-flat option. This does not mean the Universe is definitely curved — the uncertainties are still large, and a flat model cannot be ruled out. But there is a hint. If space is indeed curved, the familiar picture of cosmic expansion will need refinement.
Checking the shape of space is like checking how level the floor is in a huge hall. If the floor is perfectly level, a ball rolls in a straight line. If the floor is slightly concave or convex, the ball will deviate. Light from distant objects is that ball, and its path tells us about the geometry of the Universe.
If the Universe were noticeably curved, very distant galaxies might appear as their own copies — light would loop around all of space and come back from the other side.
The idea of curved space is explored in the film Interstellar, where characters travel through a wormhole, a fold in spacetime.