Ever since humans began looking at the sky through telescopes, we have gradually found ourselves in celestial terms apparently we are not so special. The earth was not the center of the universe, it was concluded. It wasn’t even the center of the solar system! The solar system, unfortunately, was not even the center of the universe. In fact, there were many essentially similar star systems, together forming a galaxy. And, wouldn’t you know it, the galaxy wasn’t unique, but one of many, all having their own solar systems, even planets, some of which supposedly host their own set of egotistical beings with an overinflated sense of cosmic importance. .
This notion of mediocrity has been incorporated into cosmology, “cosmological principle“. The gist of it is that the universe is essentially the same everywhere we look: homogenized like milk, made of common materials distributed uniformly in all directions. At the top of the cosmic hierarchy, giant groups of galaxies cluster in extended filaments and sheets around the intergalactic voids, but beyond that, the structure seems to disappear. If you zoomed out and looked at the big picture of the universe, says Alexia Lopez of the University of Central Lancashire in England, “it would be very smooth.”
Lopez compares the cosmos to a beach: If you threw a handful of sand under a microscope, the grains of sand would look like unique individuals. “You’ll see different colors, shapes and sizes,” he says. “But if you were to walk across the beach, looking at the sand dunes, all you would see is a uniform gold-beige color.”
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This means that Earth (or one of the other trillions of planets that must exist) and its tiny corners of the cosmos seem to be holding it together. not a particularly privileged place compared to everything else. And this homogeneity is convenient for astronomers, because it allows them to look at the universe in part as a reliable way to make conclusions about the whole; here in the Milky Way or in an unnamed galaxy a billion light-years away, the prevailing conditions should be essentially the same.
This simplistic ethos applies to everything from understanding how dark matter weighs down galaxy clusters, to estimating how common the conditions for life might be across the cosmos, and allows astronomers to simplify mathematical models of the universe’s past and predictions of its future. . “Everything is based on the idea that (the cosmological principle) is true,” Lopez says. “It is also a very vague hypothesis. So it’s very difficult to validate.”
Validation is especially difficult when there is significant evidence to the contrary, and a growing number of recent observations suggest that the universe may indeed be rarer and more varied than cosmologists so comfortably assumed.
If that’s the case, then humans (and anyone else out there) would actually have a unique view light years beyond, not privileged, per se, but not average either, so “average” wouldn’t be any more. a useful concept on large enough scales. “Different observers can see slightly different universes,” at least on a large scale, says Valerio Marra, a professor at the Federal University of Espírito Santo in Brazil and a researcher at the Trieste Astronomical Observatory in Italy.
Astronomers have not yet thrown out the cosmological principle, but they are gathering clues about its potential weaknesses. One approach involves searching for structures so large that they challenge cosmic smoothness although incredibly wide zoom. Scientists estimate that anything wider than about 1.2 billion light-years would disrupt the homogenous cosmic apple cart.
And astronomers have found some. Lopez, for example, has found a beast called Giant Arch– A curve of galaxies about 3.3 billion light-years away. He has found it too The Great RingA torus of galaxies 1.3 billion light-years and about four billion. The two oddities are close to each other and can be linked into an even larger structure.
The very study of cosmology also gives reason to raise an eyebrow at the cosmological principle. For example, the leftover light from the big bang, called cosmic microwave ovenIt has some large-scale mysteries incidents That doesn’t seem entirely random, says University of Michigan cosmologist Dragan Huterer. “This was never properly explained,” he says.
Some scientists have argued that potential challenges to the cosmological principle can be explained by another principle. 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 what conclusions to draw from a limited sample. Perhaps the variations observed by astronomers were the result of incompleteness, rather than a true reflection of the properties of the universe; perhaps what appears to be an anomalous stroke of cosmic smoothness would flatten out compared to an unseen part of the cosmos next to the visible volume.
And when it comes to studying the right big chunks of the universe, cosmologists are really very limited: the observable universe is so big. “If you say, ‘I’m going to study the shapes of galaxies,’ well, lucky you: you’ve got billions and billions of galaxies in the universe.” You can answer your questions with statistics, and your sample variance will be very small,” says Huterer. At larger scales, you only get a few samples because the observable universe is broken up into many large parts.
Marra thought for a while that some cosmological discrepancies might be the result of cosmic variance. But it’s not enough to explain more, according to him and others calculations.
However, most cosmic observations adhere very well to the cosmological principle. So, even if scientists have enough information to reasonably question the validity of the idea, they are not at all ready to abandon it—not least because no one has a solid alternative scheme to replace it.
“There is no smoking gun evidence of violating the principle,” Huterer says. “However, there are some very interesting anomalies.”
However, it is difficult to decipher due to the nature of cosmology. “Unlike some lab experiments that you can do over and over again,” Huter says, “you get only one universe.”
