⇧ [VIDÉO] You may also like this partner content (by ad)
The standard model of cosmology, which describes all stages of the evolution of our universe and its contents, is based on the Friedmann-Lemaître-Robertson-Walker metric. This describes the average geometry of the great universe; it is generally accepted that space-time on the cosmos scale has a homogeneous and isotropic geometry. In other words, the universe appears almost identical in all directions, regardless of the position of the observer. This is what scientists call “the cosmological principle of homogeneity and isotropy”. A team of researchers recently questioned this assumption.
The cosmological principle of homogeneity and isotropy was introduced by Albert Einstein in 1917, when he tried to apply the theory of general relativity to the entire universe. Since then, the homogeneity of the universe has been supported by astronomical observations over ever-greater distances; the hypothesis is supported in particular by the extreme regularity of the cosmic microwave background (CMF), which exhibits temperature fluctuations of only about a fraction out of 100,000 on small angular scales.
The FDC fluctuations that we perceive on Earth are due to our planet’s movements in the solar system, but also the movements of our own galaxy in the universe – just as the frequency of an ambulance siren seems distorted to us as it passes closer. to us. If the standard model follows the cosmological principle well, the same distortion must be observed in very distant galaxies. Thus, in 2002, astrophysicists confirmed the hypothesis of a catalog of galaxies, the NRAO VLA Sky Survey (NVSS). However, the sample of galaxies was relatively small and there were uncertainties in their distances, leaving some scientists skeptical about the results obtained.
A universe that is not really symmetrical
Subir Sarkar, a physicist at the University of Oxford, has been interested in the question and has recently presented evidence to suggest that our understanding of the universe is in fact completely deficient – the models and theories established so far to describe the cosmos. , would not be universal. From our earthly perspective, the universe appears to be expanding at a given rate, but it may just be a matter of perception, biased by the fact that our own galaxy itself is moving through the universe.
His hypothesis is based on the study of the catWISE catalog, which shows 1.4 million quasars detected by the WISE space telescope (this catalog has the advantage that it covers a larger part of the sky than NVSS). In a study published last year in The Astrophysical Journal Letters, the physicist and his team explain that they have discovered a distortion in the distribution of these quasars, twice as large as that predicted by theory. Their results thus suggest that it is not only galaxies and all other astronomical objects that drift through the universe, but that the entire universe can also drift in a certain direction.
” If it is determined that the distribution of distant matter in the large universe does not share the same frame of reference as the FDC, then it will be imperative to ask whether the differential expansion of space produced by the non-linear structures close to cavities, walls and filaments can be effectively reduced to a simple local “nudge” “, The researchers conclude in their study. If further work is needed to clarify things, Sarkar and his co-authors believe it may be necessary to establish a whole new cosmological framework that does not assume that all directions are equal. Specifically, it would be necessary to solve Einstein’s equations differently.
A “cohabitation” of several cosmological models?
Of course, most scientists are not ready to accept that the universe is asymmetric and that current theories are biased. Some believe, for example, that the results obtained by Sarkar could be due to the fact that quasars tend to agglomerate more than other types of objects on these scales, which would not fundamentally challenge the standard model.
The physicist points out that our universe could also be based not on a single cosmology capable of describing everything, but on several models, each of which applies to a different era. New generation of telescopes, especially Vera C. Rubin in Chile and the Euclid Space Telescope, not to mention the Square Kilometer Array, which will soon scan billions of very distant galaxies, may help shed light on the debate.
Note that Sarkar is not the first to question the cosmological principle. Two methods are generally used to calculate the Hubble constant – the rate of expansion of the universe. One is based on the analysis of FDC, the other is based on the study of standard light (astronomical objects with known brightness). However, researchers achieve different values depending on the strategy used: 67.4 km / s / Mpc or 74 km / s / Mpc, respectively. This inexplicable discrepancy, called the “Hubble Tribe”, suggests that our cosmological model is incomplete – although recent work has shown that this difference could simply be due to measurement errors.
Likewise, the recent discovery of a giant arc spanning more than 3 billion light-years, consisting of galaxies and galactic clusters, is also against established models of the cosmos. This megastructure, called the Giant Arc, which makes up about 7% of the observable universe, simply should not exist if matter is evenly distributed in all directions. In fact, the current theoretical limit, according to cosmologists, is estimated at 1.2 billion light-years. ” The growing number of large structures that exceed the size limit of what is considered theoretically viable is becoming increasingly difficult to ignore “, Emphasized at the time Alexia Lopez, at the origin of the discovery.