In early Studies of other galaxies, scientist thought that the expansion of the universe was slowing due to gravity. Scientists were certain about the expansion of the universe. Theoretically, scientist thought the universe might have enough energy density to stop its expansion and re-collapse or it might have so little energy density that it would never expanding, but the scientists were certain gravity slowed the expansion as time went on.  In reality, scientists had no evidence that the expansion was slowing, but in theory, they were certain the slowing was taking place due to the fact that the universe is full of matter and the attractive force of gravity pulls matter together.

This thought changed in 1998 when two independent teams of astrophysicists observed a very distant supernovae. They used Hubble Space Telescope to calculate the deceleration. The findings showed that the universe was actually expanding faster than it was a long time ago.it was observed that the universe expansion was actually accelerating, no one expected the findings, and these findings changed everything. The earlier thought that the universe expansion slowed due to gravity changed, scientist were left in a dilemma they could not explain it (Bahcall, 23).

With time scientist and theorists came up with explanations. They came up with three explanations, in one of the explanations theorist thought maybe it was a result of a long dropped version of Einstein’s theory of gravity. The theory contained the term “cosmological constant” this was a term Einstein included in his field equation, he included it for general relativity because he was dissatisfied that his equation did not allow, supposedly, for a static universe. In another explanation, theorists thought maybe there was some peculiar kind of energy-fluid that filled space. The theorist thought that maybe there was something astray with Einstein’s theory of gravity and maybe the development of a new theory could make allowance for some kind of field that creates this cosmic acceleration.

To date theorists still do not have a correct explanation for but they have developed a name for the solution. They named it dark energy. Dark energy is a force that explains the expansion of the universe. Dark energy is still a mystery a lot about this force is unknown than is known scientist are aware of how much of dark energy there is because its effects on universes expansion are known. Dark energy remains a riddle, but it is a vital riddle.it is reported that approximately 69 per cent of the universe is dark energy while dark matter makes up about 27per cent the rest 5 percent is made up of all normal matters this includes everything on earth and everything observable through instruments (Cline, 340).

Leading theory elucidation of dark energy considers it as a property of space. Einstein was the first to conscious of the fact that space was not empty in his theory of general relativity  Einstein appreciated that space could continue to come into existence he, however, included the cosmological constant term to compliment the static universe scientists thought existed. Later after Huddle tabled the findings of the expanding universe, Einstein realized that the inclusion of the “cosmological constant” term in his theory of general relativity was a mistake. But this mistake could be the best explanation for dark energy. Einstein predicted that empty space could have its own energy because energy is a property of space itself. Einstein’s constant indicates that as more space emerges the more the energy added to the universe thus increasing its expansion (Overduin, 137). Regrettably, people do not understand the cosmological constant they can’t understand why it should even be there, or why it would have exactly the right factors to cause the observed acceleration of the universe.

The quantum theory of matter is a theory that explains how space amasses energy. The theory state that empty space is filled with temporary particles that constantly form and then disappear (Bahcall, 97). To know how much energy these particles would give, physicists did a calculation whose answer was wrong, the answer was too big and ended up increasing the mystery and dilemma on dark energy. In another elucidation for dark energy theorists suggests that dark matter is a new kind of dynamical energy fluid or field something that fills all of space but whose effect on the expansion of matter is the opposite of that matter and normal energy theorist gave this a name they called it “quintessence”. If quintessence is the solution, it is not clear what it is like, what it interacts with or the reason for its existence. So the riddle continues.

The last explanation is that Einstein’s theory of gravity could be wrong.

If this were the case, a lot would be affected from the expansion of the universe to the way normal matter in galaxies and clusters of galaxies behaved this would provide ways for scientists to decide if the solution to the dark energy problem is a new gravity theory or not. But in case a new theory of gravity is needed scientist question what kind of theory it would be and how correctly would it describe the motion of the bodies in the solar system, some think that like Einstein’s theory the new theory would make new predictions about the universe and would create more dilemma and mystery. Scientists need to conduct deep research to know more about the dark energy they should collect more and better data to understand more about dark energy possibilities.

Dark matter accounts for most of the matter in the universe.  Dark matter is unidentified type of matter. It emits no light, and it is not a star or a planet .dark matter cannot be seen directly due to the fact that dark matter is small and transparent to electromagnetic radiation, thus, cannot absorb or emit enough radiation that can be detected by current imaging technology (Overduin, 123). For this reason, we can say dark matter is not in the form of dark clouds of normal matter made up baryons because baryonic clouds can be detected by their absorption of radiation passing through them. Dark matter is not antimatter because unique gamma rays that are produced when antimatter annihilates with matter cannot be seen.

Is dark matter a possibility does it exist, there are few dark matter possibilities that are viable Baryonic matter could still make up the dark matter if it were all tied up in brown dwarfs or in small, dense chunks of heavy elements. These possibilities are known as “MACHOs”. But the most common view is that dark matter is not baryonic at all, but that it is made up of other, more exotic particles like axions or WIMPS. Up to now a lot is unknown about dark energy and dark matter scientist are investing more resources and collect more data and better data to ensure the mystery is solved.

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