Navigating the universe may be more mind-bending than we thought.
If our universe takes the shape of a three-dimensional, finite donut, we can imagine a spacecraft traveling in one direction, and eventually ending up where it began. Something like this might actually be the case, according to an initial Live Science report.
"We could say: Now we know the size of the universe," said Thomas Buchert, an astrophysicist of the University of Lyon, in the France-based Astrophysical Research Center, in the report. This idea has yet to be proven, but it would provide new and bizarre clues about the universe's behavior, structure, and final fate.
A donut-shaped universe
If we live in a donut-shaped universe, the first two things we'd know are the following: The cosmos is finite, and far smaller than we thought (only three to four times larger than we can currently see). This is significant, despite our limited telescopic range of study. This would also imply that the universe will ultimately collapse in on itself, instead of expanding outward forever, read the Live Science report. This is a question that begets many more, but there exists plenty of evidence to lend credibility to the "big donut" hypothesis. To map the topology of the universe, the astrophysicists measured disruptions in the cosmic microwave background (CMB), which is an ambient background noise of the universe's beginning, in the Big Bang.
"In an infinite space, the perturbations in the temperature of the CMB radiation exist on all scales," said Buchert in an email to Live Science. "If, however, space is finite, then there are those wavelengths missing that are larger than the size of the space." The researchers discovered that there's a maximum limit to the size of the disruptions in the universe. Unless there was an error in the analysis, this means the universe closes in on itself, since a cosmos opening out into infinity could support CMB perturbations of every size. But even if the universe is finite and donut-shaped, a spacecraft wouldn't be able to "loop around" to its starting position after traveling across the surface of the cosmos. This is because the universe is still expanding faster than the speed of light, which means that — barring the discovery of a means of faster-than-light travel — no one could ever go so far as to arrive where they started.
Cosmic perturbations at large scales missing from data
NASA's WMAP and the ESA's Planck satellites assisted the scientists as they built their maps of the CMB, and they revealed an exceptional number of missing perturbations at large scales. Having concluded that the limited size of perturbations implies a three-dimensional donut, or a three-torus, according to its mathematical name. "We find a much better match to the observed fluctuations, compared with the standard cosmological model which is thought to be infinite," added Buchert in the report. "We can vary the size of the space and repeat this analysis. The outcome is an optimal size of the universe that best matches the CMB observations."
"The answer of our paper is clearly that the finite universe matches the observations better than the infinite model," said Buchert. If this three-torus (or big donut) theory of the universe is later confirmed, astrophysicists may one day report that we finally know the size of the universe, whether or when it will begin to collapse in on itself, and more.