For decades, cosmologists have built their theories on the assumption of a cosmos identical in all directions, a fundamental premise for tracing its history. This simplified approach has the advantage of making the equations of gravitation solvable and producing models with predictive capabilities.
This postulate of isotropy is at the heart of the standard cosmological model, often called Lambda-CDM. It describes the dynamics of the Universe on a large scale, incorporating dark matter and dark energy. However, some recent observations seem to contradict this beautiful symmetry, casting doubt on our current representations.
Credit: Pixabay/CC0 Public Domain
Among the anomalies shaking the model, one of the most striking concerns the cosmic microwave background, this residual light from the Big Bang. Its distribution across the sky shows a slight temperature deviation, known as the dipole. According to established theories, this signature should be reflected in the distribution of matter at great distances.
To test this hypothesis, astronomers have developed the Ellis-Baldwin test, which compares the deviations of the cosmic microwave background with those of distant sources like quasars. The results, obtained thanks to recent data catalogs, show a clear disagreement. The measurements do not match, regardless of the observation method used, whether by radio telescopes or satellites.
This inconsistency, named the cosmic dipole anomaly, directly challenges the FLRW theoretical framework on which the standard model is based. It cannot be explained by measurement errors, as it is confirmed by different techniques. The implications are profound, perhaps forcing us to completely rethink our description of spacetime.
Map of the cosmic microwave background taken by ESA's Planck satellite.
Credit: ESA and the Planck Collaboration
New instruments, like the Euclid telescope or the Vera Rubin Observatory, will soon provide an avalanche of data. This information could pave the way for innovative cosmological models, thanks to the support of artificial intelligence tools, and perhaps lead to the discovery of novel physical phenomena.
If this lead is confirmed, our understanding of the Universe could evolve significantly. The coming years will allow us to verify whether solidly anchored concepts need to be revised, thus opening up new perspectives.