The universe is the vast expanse that contains all of space, time, matter, and energy. It includes everything from the smallest particles to the largest galaxies. Scientists believe the universe began with the Big Bang around 13.8 billion years ago, leading to its continuous expansion. Within the universe, there are billions of galaxies, each containing millions or even billions of stars. Our own galaxy is called the Milky Way. The universe is governed by physical laws, such as gravity, which influence the movement of celestial bodies and the formation of structures like planets and stars.