These few paragraphs provide a brief overview of how energy is believed to evolve from beginning to end. A most basic fact is that the universe evolves: We do not live in a static cosmos. Total energy in the universe is constant, but its form is steadily evolving from a low entropy to a high entropy form. All forms of energy, such as matter, fission, fusion, and kinetic and potential energy are precisely offset by the negative gravitational potential of everything. All energy is contained either in matter or force fields and the theoretical Higgs field which imparts mass to certain particles (as protons, neutrons and electrons).
The universe not only expands but the expansion is accelerating. All appears to have started from a bang, perhaps infinite, perhaps finite, depending on the model of your choice, but the universe began from a very high energy, high temperature, unstable state.
It evolves towards a more stable lower temperature state and might eventually reach absolute zero in the big bang model. Inflationary energy created exponential expansion just after the big bang and such energy decays into radiation via quantum mechanical processes. Cyclic models reflect repeated expansions and contractions powered by the endless cycling of energy between gravity, forms of dark energy, kinetic and potential energy.
In the beginning it’s believed most energy was in the form of heat radiation and inflationary (vacuum) energy from which space, time, and matter evolved. As the universe expands, the total vacuum energy increases and its repulsive nature causes space to expand even faster…in a run away exponential expansion. In the big bang model, dark energy powers an accelerated expansion after 9B years as it over powers the gravitational attraction of matter. [we are in this phase currently]
Matter energy density decreases as volume grows and matter spreads out; while radiation energy density not only decreases but its wavelength is stretched further by expansion depleting its energy faster, so radiation density falls faster than the energy density of matter. Dark matter energy density remains nearly constant. Dark matter dominated the past; dark energy will dominate the future.