Jess and Mitch try to explain the Big Bang theory, a scientific explanation for the origin and evolution of the universe. They discuss how the universe began as a tiny, hot, dense speck that exploded, causing the universe to expand rapidly. This conversation uses analogies, such as raisin bread dough and popcorn, to help viewers understand complex concepts like the expanding universe and the Cosmic Microwave Background (CMB) radiation. They also discuss the evidence supporting the Big Bang theory, including redshift, the abundance of light elements, and the detection of the CMB.