The Radiantverse was formed when a normal universe was producing many massive and varied stars at once. At the same time, millions of new and close by galaxies were being formed as well. More than 2 trillion stars were made in the timespan of a few months (in ONE galaxy). This went on for a while (and some say it still is) until the stars started dying. After that so much and so many different types of radiation was expelled at once the started going to turmoil. It's currently uninhabitable by most people due to the massive amounts of radiation (even on the planets).