Simulated view of the formation of our Milky Way galaxy. The simulation begins moments after the birth of the universe 13.8 billion years ago and ends with our mature, present-day Milky Way galaxy. Pockets of matter are seen growing in size, and merging with each other, due to the force of gravity. The clock in the corner denotes the passage of time using a convention astronomers refer to as redshift, or “z.” The universe begins at a z value of 30, while the present-day has a z value of zero.