The Shape of the Universe: Flat, Open, or Closed?

The universe’s shape describes how space itself is curved on the largest scales.
A flat universe means parallel lines never meet, and geometry works as we know it.
An open universe has negative curvature, like a saddle, expanding forever.
A closed universe curves like a sphere, potentially allowing space to loop back on itself.
The shape depends on the balance between matter, dark matter, and dark energy.
Cosmic microwave background measurements suggest the universe is very close to flat.
In a closed universe, traveling far enough in one direction could bring you back to where you started.
An open universe would keep galaxies drifting apart endlessly, with no bound.
The exact curvature is so subtle that it requires precise satellite measurements to detect.
Knowing the universe’s shape helps predict its ultimate fate—eternal expansion or a cosmic collapse.