The universe seemed to scientists too homogeneous

Фото Getty Images

Фото Getty Images

Astronomers have found that the universe is more homogeneous than it should be according to conventional theory. Is this an observation error or a door to a new physics?

An international team of scientists received amazing result: galaxies are scattered more evenly across space than would be expected from mainstream theories. Will new data change our understanding of the universe?

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Today, almost none of the professionals doubt that the Universe in its current form arose about 13.8 billion years ago as a result of the Big Bang. The biography of the world has been reconstructed from infancy. We know when the first atomic nuclei were formed (just a few minutes after the Big Bang), when they combined with electrons to form the first atoms (after hundreds of millennia) and when the first stars lit up (after hundreds of millions of years).

These are not unfounded fantasies, but rigorous theories from which verifiable facts follow. Moreover, many facts, from the relict radiation to the exact chemical composition of stars, were first discovered by cosmologists at the tip of a pen, and only then confirmed by observers (with a long list of such confirmations in English you can read here). It is these predictions that have come true in science that are the main sign that the theory is working.

However, the word “theory” should not be misleading. For scientists, it does not mean something unconfirmed, suggesting possible alternatives, but simply a model that links established facts and predicts not yet established ones. The expression “Big Bang theory” does not mean that the Big Bang is something dubious, just as the expression “solid state theory” does not mean that someone doubts the existence of solids (by the way, it is about the same with the biological term ” evolution theory”).

Dark secrets

Today, the Standard Cosmological Model, also known as the ΛCDM model, dominates cosmology. This construction combines ideas about the Big Bang and the expansion of the Universe with data on mysterious substances – dark matter and dark energy.

Recall that dark matter is a substance invisible in any telescopes, which manifests itself only by its gravity. The very fact of the existence of dark matter has been established quite reliably, but its nature is mysterious. Undoubtedly, some of it is made up of very faint astronomical objects (cold gas, black holes, and so on). However, most experts believe that the lion’s share of dark matter falls on one or another exotic particles, not yet discovered by experimental physicists, and now this is more a popular hypothesis than a proven fact.

Dark energy is something that accelerates the expansion of the universe. It was for its discovery that Brian Schmidt and Adam Riess were awarded the Nobel Prize in Physics in 2011.

The very fact of the accelerated expansion of the Universe has been reliably established in several ways. But what the dark energy that provides it is is debatable. At the moment, theorists believe that this is a kind of property of the vacuum.

So, the ΛCDM model combines perfectly proven concepts (the Big Bang, the expansion of the Universe, the synthesis of the first atomic nuclei, the fact of the existence of dark matter and dark energy, and much more) with well-argued, but still not yet proven hypotheses (for example, about the nature of dark matter and dark energy). In some places, there are just blank spots filled with the most plausible assumptions.

This is a normal situation for scientific theory. Only in religion and ideology are there doctrines in which each letter is proclaimed equally certain.

Is everything smooth in the universe?

One of the important concepts in standard cosmology is the idea of ​​seed inhomogeneities. Experts believe that already in the first moments of the life of the Universe, matter was not completely evenly distributed in space. The denser clusters of matter gave rise to stronger gravity. This gravitation gathered more and more masses of matter around the heterogeneity. From this, the attraction intensified, and so on in a vicious circle. Eventually, a galaxy surrounded by emptiness (more precisely, extremely rarefied intergalactic gas) emerged around the tiny initial density fluctuation.

However, galaxies are not the most impressive objects that have arisen from seed inhomogeneities. The “Star Islands” are united into clusters, and those – into superclusters. The largest structures in the Universe, the so-called filaments, are made up of superclusters of galaxies. They form a kind of cobweb or honeycomb filling the space. The spaces between the filaments are voids (voids), in which there are almost no galaxies.

Moreover, all sufficiently large (from hundreds of millions to billions of light years) sections of this web are similar to each other like two drops of water. If you’ve seen one such region of space, you’ve seen them all. This property is called the large-scale uniformity of the universe.

But scholars are not content with hackneyed comparisons. They measure the uniformity of space quantitatively. This value can tell a lot about how the world works.

The point is that cosmologists have two ways to reconstruct the pattern of seed inhomogeneities. First, they observe a cyclopean web of filaments and voids, which was eventually formed by these fluctuations. And secondly, relic radiation is at the service of astronomers.

This radiation was separated from matter even in the era of the formation of the first atoms. But it still contains traces of how matter was distributed in space in those distant times. The relic radiation is inhomogeneous, because the substance that emitted it was inhomogeneous. This is hello to inquisitive humanity from the first hundred thousand years of the history of the Universe.

It should be noted that the Nobel Prize in physics was also awarded for the discovery of relict radiation (to Arno Penzias and Robert Wilson in 1978), and a separate “Nobel Prize” in 2006 was awarded to the discoverers of the inhomogeneities of this radiation, John Mather and George Smoot.

When scientists have two ways to measure the same quantity, it’s time to compare the results. The ΛCDM model predicts how the CMB inhomogeneities and the degree of (in-) homogeneity of the present Universe with its filaments and voids should be related. This is where a very, very interesting fact came to light.

Error or discovery?

Recently, an international team of researchers from 18 scientific centers submitted a scientific article to the prestigious journal Astronomy & Astrophysics, the preprint of which is in the public domain… In a nutshell, the result is this: the modern Universe turned out to be 8% more homogeneous than it should be according to the data on the relic radiation. This may indicate either inaccuracies in measurements, or that it is time to make changes to the ΛCDM model.

Astronomers used data from the Kilo-Degree Survey (KiDS-1000), which covered more than 31 million galaxies at distances up to 10 billion light years from Earth. The authors supplemented this information with information from the 2-degree Field Lensing Survey (2dFLenS), in which more than 70 thousand objects were observed at the same distances. The scientists also turned to the Baryon Oscillation Spectroscopic Survey (BOSS), which includes data on more than 1.5 million galaxies at a distance of up to 8 billion light years.

Comparing all this information, experts calculated the degree of homogeneity of the universe. And it turned out that it is 8.3 ± 2.6% more than expected based on the properties of the relic radiation.

How reliable are these numbers? After all, each measurement result can theoretically turn out to be a false alarm, the product of small but inevitable random noise in the original data.

The reliability of the new result is 2 or 3 sigma (depending on the calculation method). This means that the probability of its “noise” nature is either 5% (with a 2 sigma confidence) or 0.2% (with a 3 sigma confidence). By strict scientific standards, such numbers do not make it possible to confidently claim a discovery. There are examples of results with a confidence level of 2-3 sigma that, when measured more accurately, would dissipate like smoke.

Thus, the revealed excessive homogeneity of the Universe cannot yet be considered a reliably established fact. We need calculations based on even more extensive data. Then, perhaps, it will turn out that we have learned something fundamentally important about the world in which we live, and cosmologists will be forced to make adjustments to their theories.


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