Matters that we know such as planets, stars, galaxies, trees, rocks, etc they are only 5% of the universe. About 27% is dark matter and 68% is dark energy. Both dark matter and dark energy are invisible to us. So, how do we know that dark energy exists? What research has been done about it? If all these questions come to your mind and you want to know about them, then this article is for you. Today, I am going to unlock the details of dark energy. In this article, you will know -
1. What is dark energy?
2. What is dark matter?
What is dark energy?
Dark energy occupies about 68% of the universe. It appears to be associated with the vacuum in space. It is evenly distributed throughout the universe, not just in space but also in time. In other words, its effects do not mix with the expansion of the universe.
If we talk about its gravitational force, then the dark energy has no local gravitational effect but has a global effect on the universe as a whole. This leads to a repulsive force that helps to accelerate the expansion of the universe.
The rate of expansion and its acceleration can be measured by observing the expansion of the galaxy with the Hubble Telescope. These measurements, along with other scientific data, have confirmed the existence of dark energy which provides an estimate of how much of this mysterious substance exists.
In the early 1990s, we knew that our universe was constantly expanding. We were sure of one more thing about its expansion. It was that the energy density of this universe was so limited that at some point it will stop spreading and eventually it will merge again at one point, or its energy density is so high that it will always be expanding.
Here you might be wondering what is this energy density? Energy density is like the amount of energy that we can store in a substance or system. In simple words, if the energy density of a substance is high, it means that there is more energy stored in that substance.
Scientists had estimated that either the universe would merge in one point or it would continue to spread according to its energy density. But according to the theory, one thing was absolutely certain that the gravitational attraction will slow down the speed of expansion of the universe with the passage of time.
Scientists were believed this because they believed that the universe was made up of commonly visible substances and his gravitational attraction binds the whole universe. Due to the gravitational attraction, it was natural for the speed of its expansion to slow down.
But in 1998, Hubble Telescope took a picture of a supernova, which showed that in the past the rate of expansion of our universe was slower than it is now. This meant that the speed of its expansion was increasing rather than decreasing. Which was contrary to the theory of the time.
After that everyone knew there is something that is happening but no one was able to explain it. Finally, to solve this problem, they imagined some kind of energy that exists in the empty places of the universe. They named that energy as Dark Energy.
Dark energy is quite strange and mysterious. It is present everywhere around us, but we can neither measure it nor test it. But one can see its impact very clearly. Everywhere there is empty space in the universe, new creations are happening every second.
It seems like dark energy is some kind of energy that can belong to empty space because empty spaces have more energy compared to everything else in the universe. There are many ideas about what dark energy can be.
The first idea is that dark energy can be a property of empty spaces in the universe. Albert Einstein was the first person who said that empty spaces just appear to be empty but they have some amazing qualities. The first quality that he said was that the empty space in the universe can be created by itself and its quantity can increase with the spread of the universe.
In his Theory of Gravity, he referred to a cosmological constant and told that empty places have an energy of their own. The more the empty space increases, the more this energy will also increase. So that this universe will continue to spread forever. But at that time he could not explain what was the need of this cosmological constant. For which his theory was rejected. Perhaps this cosmological constant is dark energy.
The second idea is that this empty space is actually temporary and filled with virtual particles. These are constantly created automatically and become invisible somewhere. The energy located in these particles can be dark energy. But there is a problem out there.
When the physicists tried to calculate how much energy such energy could provide to an empty space, their calculation proved to be wrong. Because it was 10^120 times more than the actual dark energy. That is why dark energy still remains a mystery to us.
The final idea is that maybe Einstein's theory of gravity is wrong and we need to understand it again. Or we need a theory that can explain every quality of the universe. But what could be such a new theory?
Due to Einstein's Theory of Gravity, we have not only understood the behavior of celestial bodies present in the universe but have also got them right. In such a situation, it is difficult to imagine a completely new theory. That is why Dark Energy is still mysterious to us.
What is dark matter?
Dark matter is made up of such particles that do not absorb, reflect, or emit light, that is why we cannot see it directly nor be detected by observing electromagnetic radiation such as x-rays or radio waves. But it covers about 27% of the universe so it is even more important to know about this matter.
It has some effect on objects that is why scientists have pretty sure that it exists. They study dark matter by looking at its effects on visible objects. Dark matter in the universe is empty spaces that divert the direction of light, which indicates their presence.
Most scientists believe that it may be made of nonbaryonic subatomic particles (Hypothetical subatomic particles). All the substances we know so far, such as electron, proton, and neutron, all come in the baryonic matter.
This means that the dark matter is made up of such particles that we do not yet know. The discovery of such particles can take our science forward many times. According to scientists, the particles that are searching for are named WIMPs (Weakly Interacting Massive Particles).
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