The Conflagration

Following The Great Union, the sudden expansion and cooling of the universe was known as The Conflagration. As Todra's energy dispersed into Nifra's vacuum, the energy began to vibrate and spread quickly, exploding outward in all directions and cooling as it did so. During this cooling and expansion process, energy began to coalesce into matter, first as hot plasmas and gasses, but then as trace elements such as hydrogen and helium.
Over time, more elements were forged, and gravity began to pull them together to form globes of matter such as galaxies, stars, planets and moons. In this way, Todra and Nifra became the universe, discovering what it was like to be new and exciting states of matter.
Planets and moons and suns weren't the only thing created during the Conflagration, however. A whole new host of primordial gods was born, each representing a different aspect of universal law. There were the gods of attraction and repulsion, of heat and cold, of motion and stillness, to name a few. Each god had an equal and opposite god, and altogether they embodied the universal laws of physics, enforcing these laws in a rational, logical and unerring manner, in order that the fledgling universe would have a sense of order and stability to it. (In fact, order and chaos were two of the gods of Periva.)
Following the Conflagration and the formation of the universe, the gods turned their eyes toward creating the first mortal life, in a shift known as The Dawn of Mortality.