Imagine a universe where you could point a spaceship in one direction and eventually return to where you started. If our universe were a finite donut, then such movements would be possible and physicists could potentially measure its size.
"We could say: Now we know the size of the universe," astrophysicist Thomas Buchert, of the University of Lyon, Astrophysical Research Center in France, told Live Science in an email.
Examining light from the very early universe, Buchert and a team of astrophysicists have deduced that our cosmos may be multiply connected, meaning that space is closed in on itself in all three dimensions like a three-dimensional donut. Such a universe would be finite, and according to their results, our entire cosmos might only be about three to four times larger than the limits of the observable universe, about 45 billion light-years away.
Physicists use the language of Einstein's general relativity to explain the universe. That language connects the contents of spacetime to the bending and warping of spacetime, which then tells those contents how to interact. This is how we experience the force of gravity. In a cosmological context, that language connects the contents of the entire universe — dark matter, dark energy, regular matter, radiation and all the rest — to its overall geometric shape. For decades, astronomers had debated the nature of that shape: whether our universe is "flat" (meaning that imaginary parallel lines would stay parallel forever), "closed" (parallel lines would eventually intersect) or "open" (those lines would diverge).