Mathematics
Non-Euclidean Geometry and the Shape of the Universe
Quick fact
Astronomers have measured the geometry of the universe using the cosmic microwave background and found it to be remarkably flat—to within about 0.4%—meaning parallel lines could extend forever without meeting, even though gravity curves spacetime locally.
Why this is interesting
We all learned that parallel lines never meet and triangles have 180°. But what if the universe itself is curved, bending these rules on a cosmic scale?