Instead of being flat like a bedsheet, our universe may be curved like a giant balloon filled with air, according to a new study published in the British journal nature astronomy on November 4.
The study examined data from the cosmic microwave background (CMB), the faint echo of the big bang. But not everyone is convinced: the new study, based on data released in 2018, not only contradicts years of conventional wisdom, but also contradicts another recent study based on the same set of CMB data sets.
If the universe is curved, it is gently so, according to the new paper. This gentle curvature is not important to our lives or to the workings of our solar system or even our galaxy. But out of all this, far beyond our region of the Milky Way, into the darkness, and eventually — in a straight line — you’ll circle back to where you started.
Cosmologists call this concept the “closed universe.” It’s been around for a while, but it doesn’t fit with existing theories about how the universe works. As a result, it was largely rejected in favor of the theory of a “flat universe,” which held that the universe stretched infinitely in every direction and did not form a loop of its own.
According to the paper’s authors, the most accurate measurements of the CMB to date show anomalies that provide solid, but not conclusive, evidence that the universe is closed after all. The authors include university of Manchester cosmologist eleonora di valentino, university of Rome cosmologist alessandro melchiori, and Johns Hopkins university cosmologist Joseph silko.
The difference between an open and closed universe is a bit like stretching a sheet and inflating a balloon, melchiori says. Either way, the universe is expanding. As the sheets expand, each point moves away from the others in a straight line. When a balloon is inflated, every point on its surface moves away from all the other points, but the curvature of the balloon complicates the geometry of the motion.
“This means, for example, that if there are two photons traveling parallel in a closed universe, they will eventually meet,” melchiori said. In an open, flat universe, the two photons — undisturbed — would travel in parallel paths and never interact.
Traditional models of the expansion of the universe imply that the universe should be flat, melchiori said. According to this model, rewind the expansion of space back to the very beginning, the first 10-25 seconds after the big bang, and you’ll see an incredibly exponential expansion of space as it emerges from that very tiny point where it started. This ultra-fast expanding physical property points to a flat universe. This, he says, is why most experts believe the universe is flat in the first place.
If the universe were not flat, melchiori said, the physics of the creation mechanism would have to be “fine-tuned” so that it could be linked together, and countless other calculations would have to be redone in the process. This, the authors of the new paper write, may ultimately be inevitable.