There are two mysterious things in the universe. Mysterious because we don't know what those are; the one is dark energy and the other is dark matter. Of the total energy/matter in the universe, the dark energy is about 67 percent and the dark matter about 28 percent, and the rest five percent constitutes the matter that we know. Does that mean we know five percent of the universe, the answer would be absolutely not? Then how do we know that dark matter and dark energy exist?
The existence of dark matter is inferred from its gravitational effect on the movement of stars and planets within most of the galaxies and the accelerated expansion of the universe is explained by a mysterious force termed dark energy. The term universe means the observable part, which is about 92 billion light-years across, and the parts beyond that will always remain out of reach because of expansion. Now the dark matter.
Ever-since it was hypothesized, search for the particles constituting the dark matter has been ongoing, with several candidates considered and discarded. The difficulty arises because whatever constitutes the dark matter, neither emits/absorbs light nor reacts with the known matter. The latest particles under consideration as a serious candidate for the dark matter are axions and underground detectors filled with xenon are looking for hints of the existence of such particles.
The theoretical basis for axions is based on the charge-parity-time symmetry problem of the strong nuclear force that theorists believe can be explained by the existence of an additional field whose excitation would give axions. The name itself came from a detergent as it would clean up a nagging problem. It's a matter of time before axions as the dark matter particles are either confirmed or discarded.
Fundamentally, it's only minuscule that we know, no matter what theists and atheists tend to believe.
