Dark energy is one of the phenomena of the Universe, the existence of which became known twenty years ago. However, scientists to this day do not know much about its nature.
When Einstein at the beginning of the last century deduced the equation of gravity, he assumed that there must be a force that opposes the attraction of objects to each other. At the time, scientists assumed that the universe was static. But gravity acts in such a way that all objects with mass are attracted to each other. Therefore, in order for the Universe not to collapse, some force must oppose gravity. And Einstein introduced a cosmological constant into the equation, which was supposed to balance gravity. But from the obtained equality it followed that the Universe is not static, but expanding, and this contradicted the theory. The scientist called the constant his great mistake, but it turned out to be a great prophecy.
In the late 1990s, researchers discovered that supernovae in distant galaxies were less bright than previously thought. That is, the distance to these galaxies turned out to be greater than that calculated using the old formulas: D = 2R / 2sin (α / 2), where D is the distance to the star, R is the radius of the earth's orbit, α is the angle at which the average radius of the earth's orbit would be seen from the center of mass of the star.
Scientists have concluded that the universe is expanding not just, but with acceleration. Then these observations were experimentally confirmed by measurements of the relict radiation irregularity (the remnant of the Big Bang energy) and observations of the formation of galaxy clusters.
CMB map compiled by the Planck Orbital Observatory / ESA
Physicists formulated a hypothesis, from which it followed that some energy does not allow the Universe to collapse, it also solves the problem of invisible mass. Indeed, according to theoretical calculations based on the analysis of the Big Bang, the mass of the Universe does not correspond to that which should be obtained as a result of calculating the contribution of all matter. It may seem strange that energy is the equivalent of mass, but this is a validated physical concept of the theory of relativity: E = mc².
Aside from influencing the expansion of the universe, little is known about dark energy. It forms our world by 68%, it has a low density, it is homogeneous and does not interact (at least so that it is noticeable) with ordinary matter, except for gravity.
The essence of dark energy is difficult to determine, as it is too different from the usual phenomena. The fact is that in physics, when describing processes, it is not the amount of energy that is important, but its change. For example, with a potential difference, a voltage arises (electrons move from one point to another), and when the temperature changes, we can determine exactly how many degrees the body has heated up or cooled down.
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Gravity is an exception to the rule here - it is acted upon by constant energy, not a difference in values. The phenomenal field that affects the rate of expansion of the universe is called vacuum energy, or dark energy. The field is spread throughout the entire space and has the same density everywhere. Errors in cosmological observations leave the possibility of assuming the presence of weak dynamics in the vacuum energy.
“The fact is that our experience with the study of the Universe is negligible in comparison with its lifetime and scale. Let's say we photograph a large old oak tree every day for several months and don't notice any changes. Based on the experiment, we conclude that the plant does not change at all over time. But, probably, our camera simply cannot detect insignificant changes, besides, the experiment time is too short. It is reasonable to assume that the constancy of dark energy is only apparent, but in fact we observe a dynamic field, only it evolves very, very slowly. Therefore, it is too early to make final conclusions about the properties and essence of dark energy,”comments Dmitry Gorbunov, Associate Professor of the Department of Fundamental Interactions and Cosmology at the Moscow Institute of Physics and Technology.
But if the universe is expanding, why can't our senses feel it? The fact is that large clusters of matter (for example, galaxies) are gravitational systems. And they have a certain balance between the action of dark energy and gravity, thanks to which such systems remain stable. And the takeoff of the universe occurs due to the expansion of interstellar space.
Olga Kolentsova