*“Is our beautiful being vertical, horizontal, and / or circular?”*Aksil Tikjda asks on the page The social networking site Facebook from *Science and the future. *This is our question for this week. Thank you for your participation!

## A universe that had long been thought to be flat …

So what is the shape of the universe? For a decade, the answer seemed certain: flat. Thus, two rays of light can always travel in a straight line without meeting. However, an article published in 2019 in the magazine *Natural Astronomy* By an Italian team returning to this “flatness” that seemed to be well integrated into the prevailing cosmic paradigm. It suggests that the universe will be spherical and thus “closed”, which means that a ray of light starting from a point will eventually return to its starting point. At the moment, this is a working hypothesis that has not yet been determined and reflects the fact that cosmologists are not completely satisfied with their model.

## … but that could be spherical!

To understand, remember that Einstein’s theory of general relativity changed our concept of space and time: matter bends space and the curvature of space directs light. Within the framework of general relativity, George Lumetri and Alexander Friedman independently imagined three possible geometric shapes according to the content of the universe. Each geometry is determined by a specific curvature of space, which can be positive, zero or negative. If the density of the material is greater than a certain critical value – it is equal to 10^{-29}g / cm3, or 0 point 28 zeros followed by 1, then space has a positive curvature, the universe can be represented as a sphere with a geometry unfamiliar to us. For example, the sum of the angles of a triangle y will be greater than 180 degrees.

Such geometry assumes a closed universe, because the star’s light will eventually return to its starting point. This is the case discussed today in an article by *Natural Astronomy*. Even if it’s for more than a decade, based on data from the US Wmap probe and the European Planck Observatory, zero curvature is the one favored by cosmologists. Space in which there is no curvature is the result of a material density equal to exactly the critical density. It corresponds to a flat universe. Finally, the third geometry – hyperbolic – is that which corresponds to the density of a substance below the critical density. Then the space is hyperbolic that one can represent as a horse saddle, and the sum of the angles of the triangle is less than 180 °.

*Credit: Astronomy, Nature*

## Cosmologists are in the midst of a debate

The cosmic Wmap satellites, launched in 2001, and the Planck satellites in 2009, examined in detail the first light in the universe – the spreading cosmic background, which was emitted when the universe was 380,000 years old. These missions decided in favor of a zero curvature of space and thus a flat geometry. This favors the cosmic model called “Lambda CDM”, meaning cold dark matter lambda, where dark energy dominates the content of the universe by about 70%, which speeds up the expansion of the universe, while that dark matter – about 25% in a cold form, that is, it interacts very weakly with Ordinary Article. However, in recent years, several observations appear to contradict this model’s predictions. First, theorists and observers do not have the same estimate of the expansion rate of the universe.

Based on the hypothesis detailed in an article by a pen *Natural Astronomy*The fact that light from a diffuse cosmic background appears to be deflected by a greater amount of mass than the current model assumes. As the authors of the article point out, “*A closed universe could explain a physical explanation for this effect.*The conclusion quickly came to appease the other Article. Astrophysicists George Evestathio and Stephen Graton of the University of Cambridge explained that the gravitational anomaly could simply be the result of a statistical bias, insisting on the fact that data must be reanalysed before abandoning the universe model, which explains many other observations. One thing is for sure: cosmologists are in the midst of a debate!