Imagine a universe where one could point a spaceship in one direction and eventually return to where one started. That would have been possible if our universe was a finite donut and physicists could potentially measure its size. According to astrophysicist Thomas Buchert of the University of Lyon, Astrophysical Research Center in France, “We could say: Now we know the size of the universe.”
A team of astrophysicists and Buchert have deduced by examining the light from the very early universe that our cosmos may be multiply connected. This means that space is closed in on itself in all three dimensions, like a three-dimensional donut. Such a universe would be finite. According to their research, our entire cosmos might only be about three to four times larger than the limits of the observable universe and about 45 billion light-years away.
Physicists use the language of Einstein’s general relativity to explain the universe. The content of spacetime to the wrapping and sending of spacetime tells those contents how to interact. This is how the force of gravity is experienced. That language in a cosmological context connects the contents of the entire universe radiation, regular matter, dark energy, dark matter, and all the rest to its overall geometric shape. For decades there have been arguments among astronomers whether our universe is closed, open, or flat.
That geometry of the universe suggests that it is flat. Forever flat and open universes would continue to expand, while a closed universe would eventually collapse in on itself. From the cosmic microwave background, multiple observations have clearly stated that we live in a flat universe. Parallel lines stay parallel, and our universe will keep on expanding.
But there’s more to shape than geometry. There is also topology which is how shapes can change while maintaining the same geometric rules. At the same time, the measurement of the shapes and content of the universe tells its geometry that it is flat, and they don’t tell us about the topology. They don’t tell if our universe is multiply-connected, which means that one or more of the dimensions of our cosmos connect back with each other.