What is dark matter and dark energy?
The visible universe — the earth, the sun, other stars, and galaxies — is made up of protons, neutrons, and electrons, which together form an atom. The most astonishing discovery of the twentieth century was that this ordinary (baryon) matter accounted for less than 5% of the mass of the entire universe.
The rest of the universe consists of an unknown, invisible substance called dark matter (25%) and dark energy, which is an anti-gravity force (70%).
Scientists have not yet detected dark matter directly. It does not interact with baryon matter and is completely invisible in any type of electromagnetic radiation, including visible light, in whatever range a person sees. Therefore it is impossible to fix it with today’s technologies. Nevertheless, scientists are convinced that it exists because it opens up a noticeable gravitational effect on galaxies and galaxy clusters.
For example, according to standard physics, stars in the corners of a rotating, spiral galaxy should move much more slowly than those at the center of a galaxy where the visible matter of the galaxy is concentrated. But observations have shown that stars move at the same speed regardless of their distance from the center of the galaxy. This puzzle is solved if the scientist allows the stars near the border to feel the gravitational effect of an invisible mass, dark matter.
Dark matter also solves the specific optical illusions that astronomers encounter when observing deep space. For example, images of galaxies with strange rings and arcs of light can be explained by the fact that images of distant galaxies are distorted and magnified from massive, invisible clouds of dark matter – a phenomenon called gravitational lensing.
Scientists have several assumptions about what dark matter might be. One of the most common and accepted hypotheses is that dark matter is composed of exotic particles that do not interact with ordinary matter or light, unlike gravity. Several scientific groups are still working to generate dark matter particles in laboratories, including the CERN Large Hadron Collider.
Other scientists believe that the effects of dark matter can be explained by modifying the theory of gravity. According to such ideas, there are many forms of gravity, and the large-scale gravity that governs galaxies is different from the gravity to which we are accustomed.
Dark energy is much more unknown and its discovery in the 90s was a complete shock to science. Previously, scientists believed that the force of gravity would stop the universe from expanding over time. But when two groups independent of each other tried to measure the rate of deceleration, they found that the expansion did not stop, on the contrary, it accelerated.
Now, scientists suggest that the accelerated expansion of the universe is caused by a negative force generated by quantum fluctuations in another empty space. Moreover, as observations show, the power is getting stronger and stronger as the universe expands. For lack of a better name idea, scientists have dubbed this mystical force dark energy.
Unlike dark matter, scientists have no explanation for dark energy. According to one idea, dark energy is an unknown fifth fundamental interaction (the other four known: weak, strong, gravitational, and electromagnetic) called quintessence. This power fills the universe like a liquid.
Many scientists believe that the properties of dark energy are compatible with the cosmological constant – the mathematical solution that Albert Einstein added to his general area theory to fit his equations to the notion of a static (real) universe. According to Einstein, the constant he introduced was a negative force that resists gravity and protects the universe from self-destruction. Later, Einstein rejected his idea when astronomical observations showed the expansion of the universe. Einstein called his cosmological constant the biggest mistake.
And now, when we see the accelerated expansion of the universe and add dark energy as a cosmological constant, it already logically opens up how space-time stretches over time. But this explanation still gives scientists nothing because they do not know why this strange force exists.