Simulations of the formation of structure in an expanding universe, featuring a universe with no cosmological constant/dark energy (left), a universe with 10 times more dark energy than in our universe (center), and a universe with a very large cosmological constant/dark energy, 100 times more than in our universe (right). In the color scheme, blue colors represent high density regions of the universe where stars are forming, and red, low density. The simulations run for approximately 14 billion years. All models use the same initial conditions after the big bang. At early times, the Universe was very hot and dense. Gravity pulls matter together to form structure, while the rapid expansion caused by dark energy dilutes all matter as the Universe ages, halting star formation.