A universe is a vast expanse that contains all of space, time, matter, and energy. It includes everything we can observe, such as galaxies, stars, planets, and cosmic radiation. The universe is often described as having begun with the Big Bang, a massive explosion that occurred around 13.8 billion years ago, leading to its expansion. In addition to our own universe, scientists theorize the existence of multiple universes, often referred to as the multiverse. This concept suggests that there may be other universes with different physical laws, dimensions, or even alternate versions of reality. Each universe in the multiverse could have unique properties and histories.