Dark Matter and Dark Energy.
Matter as we know it, is a collection of physical elements, knowable by our senses and surrounding us. Atoms, stars, galaxies, trees, rocks and us, all of these belong to it. This matter accounts for less than 5% of the known universe. Rest belongs to dark matter and dark energy, analogically in about 25% and about 70%, and both are in general invisible for us. Our knowledge in this topic is quite sparse as to their advanced properties.
But what we already know?
Dark matter is the main source which makes the existance of galaxies to be possible. When we as a humanity calculated why the universe is structured the way it is, it quickly became clear that there’s just not enough normal matter. According to calculations, the known mass of the entire Universe is far too small for the galaxy to form after the Big Bang. The Milky Way should not be created at all. Therefore, there is a lack of mass in the Universe. Most likely, it is hidden in the form of invisible objects that interact gravitationally, but do not emit or reflect light, and do not react with other substances known to us. This missing mass is called Dark Matter.
So, we know there is something else inside and around us. Something that doesn’t emit or reflect light. Something dark. But besides being able to calculate the existence of dark matter, we can see it, in a way.
Astronomical observations have shown that dark matter creates "gravitational lenses" that bend light that reaches the Earth. In this way, you can even see where it's cumulative today. Astrophysicists plotted a map of its densities in space and it turns out that more or less it coincides with the location of the luminous matter, with the fact that the clusters of dark matter are much more extensive. Bright stars and galaxies are small objects immersed in a huge network of unknown dark substance. Our Milky Way with the Solar System is also immersed in such a huge dark cloud that reaches almost to the neighboring large Andromeda Galaxy.
Dark matter is probably made up of a complicated exotic particle that doesn’t interact with light and matter in a way we expect, but right now, we don’t know it.
Dark energy is even more strange and mysterious. We can’t detect it, we can’t measure it and we can’t taste it. But we can see it's effects very clearly.
When the amounts of individual forms of matter in galaxies and clusters of galaxies were determined by means of various observation techniques in the optical, radio and X-ray range, it was found that the total density of chemical elements and dark matter accounts for only about a quarter of the value postulated by the majority of theoreticians (critical density).
This was threated as a sign that, contrary to the theoreticians' predictions, we live in a hyperbolic curvature of the infinitely expanding Universe like a trumpet outlet. However, this interpretation was denied by measurements of the distribution of hot and cold areas of microwave background radiation, showing that the space is flat and the total energy density equal to the critical density. If we take into account both observations, a simple calculation implies the necessity of introducing additional energy, the contribution of which would compensate for the missing three-quarters of the total density of matter - energy.
So, dark energy seems to be some kind of energy intrinsic to empty space.
Energy that is stronger than anything else we know and it keeps getting stronger as time passes by. Empty space has more energy than everything else in the universe combined. Dark energy is probably not a thing, but just a property of space. Empty space is not nothing, it has its own energy. It can generate more space and is quite active. So, as the universe expands, it could be that just more and more space appears to fill the gaps and this leads to a faster expanding universe.
Maybe dark energy is an unknown kind of dynamic energy fluid or field which permeates the entire universe, but somehow has the opposite effect on the universe than normal energy and matter.
But if it exists, we don’t know how and where or how we could detect it. So there are still a lot of questions to answer. Our theories about dark matter and dark energy are still just theories.
