When we look out in to space we sees stars, galaxies spinning gracefully in space. All the visible things we can observe in our universe, we call them normal matter. which makeup less than 5% of all the mass in the universe the rest lies in around of absolute darkness.
The dark universe is invisible yet dominating component of the cosmos it includes a substance called Dark Matter and a force called Dark energy. Physicists believe that rest of the universe 95% of it is the made of dark matter and dark energy. While little less know about either each helps us understand the universe beyond what the eye can see.
Gravity is a force that is responsible for moving objects in order and bringing things together. Every object in the universe with mass has gravity. Planets, stars, moons and other objects in the Universe also have gravity. That’s why they orbit around each other,-Like moon orbits around earth and earth orbits the sun.
In the same way scientists believed that even stars and galaxies are held together by gravity. But when scientists were trying to measure the total mass of a galaxy cluster they found that there is simply not enough mass and visible stuff in galaxies to provide enough gravity to hold the galaxies together. So, there must be something invisible stuff inside and around the galaxies that makes these galaxies bind together. They called this unseen matter as dark matter.
Dark matter makes up about 25% of mass in the universe but its composition is still unknown. The substance neither emits nor reflects light and because of that it cannot be seen. The existence of dark matter can be inferred based on its gravitational pull on the visible universe. According to scientists this force what prevents galaxies from drifting away. Dark matter may also played a role in creation of cosmos. After the big bang dark matter formed a network of filaments across the universe and in this network the first stars and galaxies were born.
Something even more mysterious, called dark energy. Normal matter and dark matter generate gravity which holds things together. Dark energy is completely opposite to gravity; it causes things to fly apart.
Long ago scientists pictured and believed that universe is static. Later they found that universe is not static and also confirmed that the expansion of the universe is accelerating. I.e. galaxies moving away from each other, since its formation, the Big Bang. There must be some kind of energy pushing acceleration just like we need energy to accelerate car. Gravity is not behind this. There is something in space that is pushing things apart. That invisible force they called as dark energy.
Dark energy is mysterious force that fills the space between objects. That makes up about 70% of mass in the universes .Plus it has a repulsive property that contracts the force of gravity. The reason for existence of dark energy is unclear. Some theories state that it is the 5th Force of the nature. Yet another says it may help explain why the universe is expanding.
In his theory of general relativity Albert Einstein considered a repulsive force similar to dark energy that pushed space and particles apart called the cosmological constant the variable may provide the clues for space and time.
Much about dark universe is left to be discovered but with every theory and technological development secrets of the invisible cosmos will come closer to being revealed.