Evolution of the Universe. Computer artwork showing the evolution of the Universe from the Big Bang (far left) 12-15 billion years ago to the present day (far right). Immediately after the Big Bang was the Plank Era (yellow) during which all four forces were unified. This symmetry then breaks, leading to the inflation period (orange) a rapid time of exponential expansion. The universe begins to cool and atomic nuclei can form (nucleosynthesis, red). After 300,000 years (pink) atoms start to form and after 1 billion years (purple) galaxies start to form.