According to what scientists call the Cosmological Principle, our place in space is by no means exceptional. But recent observations of anomalies in the Universe may undermine this long-held assumption.
Since humans began looking at the sky through telescopes, we have gradually discovered that, in celestial terms, we apparently are not that special.
In the end, Earth was not the center of the universe. It wasn’t even the center of the Solar System! And the Solar System, unfortunately, was not the center of the universe either.
In fact, there were many fundamentally identical star systems, which together formed a galaxy, recalls .
And, as you would expect, the galaxy wasn’t specialbut rather one of many, all with their own solar systems, which They also had planetssome of which presumably have their own set of selfish creatures with an exaggerated sense of cosmic importance.
This notion of vulgarity was incorporated into cosmology, in the form of the so-called “Cosmological Principle“. Its essence is that the universe is basically the same wherever we look — homogeneous as milk, made of ordinary materials evenly distributed in all directions.
At the top of the cosmic hierarchy, gigantic groups of galaxies cluster together in extensive filaments and sheets rich in matteraround intergalactic voids, but beyond that, the structure appears to fade.
But the Cosmological Principle is very vague…
If we could do zoom out and look at the general panorama of the Universe, says Alexia Lopezastronomer at the University of Central Lancashire, in England, “it would look very smooth“.
Lopez compares the cosmos to a beach: If we put a handful of sand under a microscope, the grains of sand would look like the special individuals they are. “We would see different coresshapes and sizes. But if we walked across the beach and looked at the dunes, we would only see a uniform golden beige color.”
This means that Earth — or any of the other trillions of planets out there — do not seem to occupy a particularly privileged place compared to everything else.
E this homogeneity is convenientfor astronomers because it allows them to look at the universe in part as a reliable way to make inferences about the whole; Whether here in the Milky Way or in an unnamed galaxy billions of light years away, the prevailing conditions must be essentially the same.
It is ethos simplifier applies to everythingfrom understanding how dark matter weighs down galaxy clusters to estimating how common life-friendly conditions are throughout the cosmos, and allowing astronomers to simplify their mathematical models of the Universe’s past, as well as their predictions of your future.
“Everything is based on the idea that the Cosmological Principle is true,” says Lopez. “But it is also a very vague assumption. Therefore, it is very difficult to validate.”
Now this validation is especially difficult, explains Alexia Lopezwhen there are significant evidence to the contrary: A number of recent observations suggest, in fact, that the Universe may be stranger and have greater variations than cosmologists comfortably assumed.
If that’s the case, humans (and everyone else out there) could have a kind of special view of the light years beyond them – not privileged, per se, but also not averageto the extent that “average” would no longer even be a useful concept on sufficiently large scales.
“Different observers can see slightly different universesat least on large scales”, says Valerio Marraprofessor at the Federal University of Espírito Santo, in Brazil, and researcher at the Astronomical Observatory of Trieste, in Italy.
The astronomers have not yet thrown away the Cosmological Principlebut are collecting clues about its potential weaknesses.
One approach involves looking for structures so large that they defy cosmic smoothness, even at an extremely wide zoom. Scientists have calculated that anything larger than about 1.2 billion light years would disturb the homogeneity of the cosmic.
And the astronomers have already found some.
Alexis Lopez, for example, called Giant Bow — a curve of galaxies that extends about 3.3 billion light years — and the Big Ringa torus of galaxies about 1.3 billion light-years across and four billion around.
The two strange formations are close to each other and they may be linked into an even larger structure.
Cosmic Variance
The study of cosmology itself has also provided reasons to cast some doubts about the Cosmological Principle.
For example, the light left over from the Big Bangcalled the cosmic microwave background, has some mysterious large-scale fluctuations that don’t appear to be entirely random, notes Dragan Huterercosmologist at the University of Michigan. “This was never explained satisfactorily“, he says.
Some scientists argue that these potential challenges to the cosmological principle can be explained by another principle, the Cosmic Variancewhich refers to the statistical uncertainty inherent in astronomers’ measurements of the universe.
We are always limited by what we can see and therefore always mathematically uncertain as to what conclusions to draw from a limited sample.
Perhaps the variations that astronomers observed are simply the result of incompleteness and not a real reflection of the properties of the Universe; Perhaps what appears to be an anomalous bump in the cosmic smoothness flattens out when compared to an unobserved chunk of the cosmos adjacent to the volume visible to us.
And when it comes to studying large enough parts of the universe, cosmologists are indeed very limited: the observable universe is too large.
“If we say, ‘I will study the shapes of galaxies‘, well, how lucky are we: we have thousands and billions of galaxies in the Universe. We can address our questions with statistics and the sample variance will be very small,” says Huterer. On larger scales, you only get a few examples because the observable universe always splits into many large sections.
Marra thought for some time that certain cosmological discrepancies might be the result of cosmic variance. But it’s not enough anymore to explain them, according to the calculations he presented in one he presented in 2023.
Still, most cosmic observations they resist very well to the cosmological principle. Although scientists have enough information to reasonably question the validity of the idea, they are not ready to abandon it — not least because no one has a solid alternative theory to replace it.
“There is no concrete evidence of the violation of the Principle”, says Huterer. “However, there are some very interesting anomalies.”
Either way, this is a difficult problem to crack — due to the nature of cosmology. “Unlike a lab experiment that you can do over and over again,” says Huterer, “we only have one universe“.
