The two largest pieces of Universe, dark matter and dark energy. These are the two types of energy that we know the least about. Yet, nothing less than the ultimate fate of the Universe will be determined by them.
70% Dark energy tends to drive The Universe apart. 26% Dark matter tends to drive the Universe together. 4% which is everything else, including all stars, planets, and us.
Dark Energy and Dark Matter
Results from viewing Type 1a supernova have shown that the expansion of the universe is accelerating. Dark energy is the reason for this acceleration.
The two basic models for dark energy are that it is either energy associated with empty space (vacuum energy) and is constant throughout space and time, or it is an energy field that varies over space and time.
If vacuum energy is correct, in about 100 billion years, no galaxy outside our own will be visible. and if it is an energy field, depending on nature, expansion could stop and become a collapse, or the acceleration could increase without limit.
However, cosmic acceleration could be a sign that the law of gravity needs to be modified.
Ever since the phenomenal success of Isaac Newton in explaining the motion of the planets with his theory of gravity and laws of motion in 1687.
The unseen matter explains puzzling observations of cosmic bodies. Evidence suggests that the mass of dark matter in galaxies, clusters of galaxies, and the universe as a whole are about 5 or 6 times greater than the mass of ordinary baryonic matter such as protons and neutrons.
Dark matter is mostly composed of exotic particles formed when the universe was a fraction of a second old. The issue of dark matter existing or gravity needing to be modified will likely not be resolved until dark matter particles are detected, or ruled out by lack of detection. Physicists propose actually synthesizing dark matter to make.