Observations of the CMB give us our best chance to see the imprints of a multiply connected universe. Today, due to the expansion of the universe, it's much more likely that the wrapping occurs at a scale beyond the observable limits, and so the wrapping would be much harder to detect. When the CMB was released, our universe was a million times smaller than it is today, and so if our universe is indeed multiply connected, then it was much more likely to wrap in on itself within the observable limits of the cosmos back then. We could then use those observations to measure the total volume of the universe.īut how would a multiply-connected universe reveal itself?Ī team of astrophysicists from Ulm University in Germany and the University of Lyon in France looked to the cosmic microwave background (CMB). If we could somehow determine whether one or more dimensions are wrapped in on themselves, then we would know that the universe is finite in that dimension. While a perfectly flat universe would extend out to infinity, a flat universe with a multiply-connected topology would have finite size. They don't tell us if our universe is multiply-connected, which means that one or more of the dimensions of our cosmos connect back with each other.
While our measurements of the contents and shape of the universe tell us its geometry - it's flat - they don't tell us about the topology. That makes the shape of a donut, which is also geometrically flat. Now, take the opposite ends of the cylindrical paper and connect those. Those parallel lines are still parallel: Cylinders are geometrically flat.
Now, take two edges of that paper and roll it up into a cylinder. It's obviously flat - parallel lines stay parallel. There's also topology, which is how shapes can change while maintaining the same geometric rules.įor example, take a flat piece of paper. Parallel lines stay parallel and our universe will just keep on expanding.īut there's more to shape than geometry. Multiple observations, especially from the cosmic microwave background (the flash of light released when our universe was only 380,000 years old), have firmly established that we live in a flat universe. Flat and open universes would continue to expand forever, while a closed universe would eventually collapse in on itself. That geometry of the universe dictates its fate. Related: 8 ways you can see Einstein's theory of relativity in real life