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The Composition of the Universe: Mysteries of Dark Matter and Dark Energy

Going outside at night and looking at the sky, we can see the whole story. Planets, stars, nebulae, and quasars that exist or once existed—the whole vast world brightly colors the sky in different colors. Looking at this, you begin to understand how small you are in comparison with the gigantic space. We look at the same stars and the sun that great people before us once looked at. Einstein, Newton, Marie Curie, and Tesla once went outside and looked into the night sky; they saw the same objects as we do but perhaps perceived them quite differently. Have you ever wondered what it's all made of? What is in voids, galaxies, planets, and space dust? Many scientific discoveries started with a simple "why?" and today I will answer one of yours.

Over the past century, the space world has made an incredible breakthrough in the study of the composition of the universe. At the moment, we know that from a chemical point of view, 91% of atomic nuclei are hydrogen (H), 9% are helium (He), and less than 1% are the rest of the elements. Classical physics described the world as a set of physical objects like those listed above, but at certain moments there were inconsistencies that forced us to look at everything from a different angle.

The first such case occurred in the 1930s. Scientists have found that the galaxies in the Coma Cluster are not behaving the way they should be scientifically expected. In order for the predictions to be true, the mass of the cluster had to be 500 times greater than expected.

The second case was already in the 70s. By all the laws of physics, when rotating around a central body under the influence of the body's gravity, the farther the body is, the slower it rotates. The motion of stars around the galactic center should have obeyed the same law, but measurements showed that they rotate almost the same at all distances.

The most weighty argument against the lack of information appeared when scientists realized that the mass that is observed in galaxies is not enough for their formation; the forces of gravity could not overcome the kinetic energy of individual components, and everything would have scattered throughout the universe.

In addition to these cases, gravitational lensing was also observed, as were the rotation curves of galaxies, etc.

The answer to these phenomena was the theory put forward by Fritz Zwicky (a Swiss astronomer) back in the 1930s about "dark matter. The presence of the hidden mass explained the above dissonances. Gradually, the theory began to be supplemented. For example, by measuring the degree of curvature, one can calculate the average density of the universe and, based on this, understand its components. I quote: "The results have confirmed the model of the cosmological constant, dark energy, and a spatially flat universe with unprecedented accuracy. They did not coincide with the assumption of a positive spatial curvature, which was derived by scientists in the course of studying the cosmic microwave background radiation. In other words, the universe is flat, not curved." Judging by the data, it was ultimately determined that 5% was ordinary matter, 26% was dark matter, and 69% was dark energy.

But What are Dark Matter and Dark Energy?

Dark matter is a kind of matter that does not participate in electromagnetic interactions (therefore we cannot see it), flies freely through all objects in the universe, and is supposedly not subject to nuclear interactions. The only form of manifestation is gravity.

Dark energy is a stranger substance than dark matter. The fact is that it is absolutely evenly distributed throughout the universe; it cannot clump and form something, and it also affects the acceleration of the expansion of the universe. In fact, such a picture does not contradict the general theory of relativity, but for this, dark energy must have negative pressure.

Now that there are not so many ways to directly experimentally study dark matter and energy, this question remains one of the mysteries of fundamental physics in the 21st century. On the other hand, a small amount of information gives rise to a greater number of assumptions and hence experiments, which in the future may open our eyes to reliable answers. Let's hope that scientists will still find ways to interact to study our incredible world and its composition, and we will be one step closer to understanding the infinite.

Appel, J. (2023, June 8). Researchers May Have Spotted a Star Made of Dark Matter. If So, That’s Crazy. Popular Mechanics.

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