Since the big bang about 14 billion years ago, the universe is expanding but after so many years the expansion should’ve had stopped under the influence of gravity with time. Theoretically the expansion of the universe should’ve had stopped long ago but it is still expanding. The universe as we know it is full of matter and attractive force of gravity that pulls it together, then what might be the cause of the ongoing expansion of the universe?
The answer can be found in Einstein’s theory of General Relativity, or in the current ongoing research on some energy-fluid that fills space.
What is dark energy?
We know that dark energy exists because the universe is still expanding, it can be considered some sort of anti-gravity for understanding purposes, a sort of force that is actually much stronger than gravity and is only repulsive. Now since it is much stronger than gravity and assuming it to be the cause of expansion of universe most of the universe should be consisted of dark energy, hence after further studies it showed that almost 68% of the universe is dark energy. Dark matter makes up about 27% and the remaining universe or the matter which we see or our instruments can pursue is only about 5%. So most of the universe is made up of dark matter and dark energy which is still unknown to us.
One explanation of dark energy is that it is a property of space, Einstein was the first one to realize that space is not really empty, it has its own energy, another possibility Einstein discovered was of more space coming into existence now as more space would come into existence more and more energy would also come into existence resulting in more and more expansion of the universe.
Quantum explanation of how space acquires energy:-
Now, according to Quantum theory of matter, this states that empty space is consisted of temporary or virtual particles which keep on forming and disappearing. Another explanation is that the space contains some sort of energy-fluid or field that acts opposite of matter or normal energy, hence again a counterpart of gravity, or repulsive force which is causing the universe to expand.
As of now the mystery continues…