The universe is the term for the totality of all matter, energy, space and time that exists. It is the largest space known and encompasses everything that exists, including all galaxies, stars, planets, asteroids, comets, black holes and other cosmic objects.
The universe formed about 13.8 billion years ago from an event called the Big Bang. Since then it has constantly evolved and changed. The universe is expanding, which means all galaxies are moving away from each other. This phenomenon is called the expansion of the universe.
The structure of the universe is hierarchical and consists of different scales. Small scales include stars and planets, medium scales include galaxies and galaxy clusters, while large scales involve the overall structure of the universe, including the cosmic microwave background radiation and dark matter.
Exploring the universe is one of the most important scientific challenges, and astronomers and physicists use various methods to study and understand its properties. This includes observing light and other radiation from space, analyzing cosmic structures and carrying out simulations on supercomputers. Research in the field of cosmology has led to significant advances in recent decades, including the discovery of cosmic background radiation and dark energy.