According to the strange patterns in the light left over from the Big Bang, the universe may be flat but still ring-shaped. A new study suggests that despite all the evidence that the universe is flat as a pancake, it may actually be a giant donut. The strange patterns found in the echoes of the Big Bang could be explained by a universe with a more complex shape, and astronomers haven’t fully tested the flatness of the universe, according to one study.

flat surfaces

All observations so far show that the universe is flat. In geometry, “planarity” refers to the behavior of parallel lines when they reach infinity. Consider a tabletop: Lines that start parallel will stay that way as they move across the table.

Rather, look at the Earth. Lines of longitude start strictly parallel to each other at the equator, but eventually converge at the poles. When parallel lines intersect first, the Earth is not flat.

The same logic applies to the 3D universe. For example, the cosmic microwave background (CMB), light emitted when the universe was only 380,000 years old, is now 42 billion light-years away and is characterized by slight variations in sky temperature. The astronomers calculated the predicted magnitude of these fluctuations by comparing them with the observations. If the measured magnitudes are different from the predicted, it means that these parallel rays of light change direction in space-time and the geometry of the universe is disrupted.

But the same measurements showed that the overall geometry of the universe is flat, ignoring small-scale aberrations from galaxies and black holes. But there is more than one type of apartment. For example, draw parallel lines on a piece of paper. Then fold one end of the paper to form a cylinder to connect it to the other. The lines remain parallel as they pass around the cylinder.

In the language of mathematics any cylinder is geometrically flat, but is said to have a different topology. Cover both sides of the paper and you will form a donut or ring shape.

For another example of an odd flat shape, wrap a thin strip of paper in a circle, but rotate one end 180 degrees. The result is a Möbius strip that is still geometrically straight because parallel lines remain parallel even when they cross over each other.

Mathematicians have discovered 18 possible geometrically flat three-dimensional topologies. At least one dimension in each is self-wrapped and sometimes inverted or performing a partial spin, like a Mobius strip. In such a distorted universe, if we look away, we see a much younger (perhaps upside down) copy of ourselves. For example, if the universe were 1 billion light-years across, astronomers would see the Milky Way galaxy as it was 1 billion years ago, then another copy of it 2 billion years ago, and so on. If the universe were a giant donut, astronomers could look both ways to see such replicas.

shape of the universe

Astronomers have measured the topology of the universe in a variety of ways, from searching for repeating galaxy structures to matching circles in the CMB. All the evidence suggests that the universe is geometrically flat and has a simple, open topology.

But the article published on February 23 arXiv preprint database assumes that previous measurements are limited. Most importantly, the observations suggest that the universe revolves around itself in only one dimension and does not have a more complex topology. Additionally, CMB observations revealed some strange, unexplained anomalies, such as large patterns appearing where they shouldn’t. In fact, a universe with complex topology might explain at least some of the anomalies in the CMB. While this is not a definitive case for complex topologies, the researchers have proposed ideas for more complex direct searches such as further studies of the CMB.