A universe is a vast expanse that contains all of space, time, matter, and energy. It includes everything from the smallest particles to the largest galaxies. The observable universe is the part we can see, which is about 93 billion light-years in diameter, while the entire universe may be much larger or even infinite. There are theories suggesting the existence of multiple universes, often referred to as the multiverse. Each universe within this concept may have different physical laws and constants. This idea raises questions about the nature of reality and our place within the cosmos.