A new study suggests that the Universe is actually spherical and closed (not flat)

The study of the curvature of the Universe is an active field of research in cosmology. In recent years, the many data collected by observation missions such as WMAP and Planck have shown a locally null curvature of the Universe, indicating that the latter is certainly flat. The data match so well with each other that the model of the flat Universe is today integrated into the standard cosmological model. However, an anomaly derived from data collected by the Planck Space Observatory in 2018, concerning the cosmic microwave background, could be interpreted as a sign of a closed spherical universe.

On the basis of data collected last year by the Planck satellite of the European Space Agency, cosmologists have argued that the Universe is actually curved and closed, like an expanding sphere. This means that a beam of photons drawn in a straight line would eventually return to its starting point, crossing other beams in its path; whereas these beams would remain parallel in the scenario of the flat Universe.

According to an international team of astronomers led by Eleonora Di Valentino of the University of Manchester in the United Kingdom, their findings present a "cosmological crisis" that calls for "radical rethinking of the current model of cosmological concordance". The key in determining the curvature of the Universe lies in the way gravity curves the path of light, an effect predicted by Einstein and called the gravitational lens .

Unlike a flat Universe (zero curvature) where light beams would continue indefinitely their stroke in a straight line, in a closed Universe (positive curvature), they would eventually return to their starting point. Credits: Lucy Reading-Ikkanda

Anomaly A lens : it could be explained by a closed sphere Universe

It is not about any light but the cosmic microwave background (CMB), that is to say the electromagnetic radiation bathing the Universe, whose first emission dates back to 380,000 years after the Big Bang during a phase called Recombination (capture of electrons by atomic nuclei).

The Planck satellite data, particularly from 2018, show that CMB has a more pronounced gravitational lens effect than expected. The Planck Collaboration has called this anomaly A lens , and this has not yet been resolved, but the team believes that an explanation could be the curvature of the Universe. The study was published in the journal Nature Astronomy.

The researchers showed that the anomaly in the spectrum of the cosmic microwave background could be interpreted as the sign of a closed universe (blue). Credits: Eleonora Di Valentino et al. 2019

"A closed universe can provide a physical explanation for this, with the Planck CMB spectrum now pointing to a positive curvature of greater than 99% confidence. Here we study further evidence of a closed universe collected by Planck, showing that positive curvature naturally explains the abnormal amplitude of the lens effect, "the researchers write.

An interpretation incompatible with all current data

A curved universe may explain this anomaly, but there are several important issues, including the fact that all other analyzes of Planck datasets, including the same data from 2018, concluded that the standard cosmological model is correct, including concerning a flat universe.

There are also other problems, and the team took care to note them in its article. One is Hubble's constant, which gives the rate of expansion of the Universe; it is a real problem in cosmology today. The different measures of this constant give different values, and to consider a curved universe makes this measurement even more complex.

The interpretation of the authors of the article (red and blue) is incompatible with the current data from different missions of cosmological observation (gray). Credits: Eleonora Di Valentino et al. 2019

Data from baryonic acoustic oscillation studies on dark energy are also inconsistent with the Closed Universe model, as are data on gravitational distortion obtained from observations of weak gravitational lenses . One other article also suggests that the anomaly A lens is simply a statistical bias in the data collected.

Future studies are needed to clarify the nature of the anomaly

Astrophysicists George Efstathiou and Steven Gratton of the University of Cambridge also analyzed Planck's 2018 data and found signs of curvature. But when compared to other Planck data sets and baryonic acoustic oscillations data, they found "solid evidence to support a spatially flat universe".

Much of the data seems to be in favor of a flat universe rather than a closed universe, except for the anomaly A lens . " Future steps will be needed to clarify whether the observed discrepancies are due to undetected systematics, new physics, or simply statistical fluctuation, " the researchers conclude.


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