The universe is literally everything, the sum of all existence. It includes all matter, like stars and galaxies. The universe also includes all radiation and all other forms of energy. No matter where or when you exist, you are a part of the universe, as is everything you experience. There is nothing outside the universe, because anything that exists is automatically included in the definition of the universe.

Scientists do not know what came before the Big Bang. However, they do know that the singularity is not real; instead, it's an artifact of general relativity that occurs when the equations break down and lose their ability to describe a physical situation. A true explanation for the singularity must lie in a theory of quantum gravity, which is a physical theory of strong gravity at extremely tiny scales. Physicists do not currently have such a theory, but they do have several candidates, like string theory and loop quantum gravity.

The universe is literally everything, the sum of all existence. It includes all matter, like stars and galaxies. The universe also includes all radiation and all other forms of energy. No matter where or when you exist, you are a part of the universe, as is everything you experience. There is nothing outside the universe, because anything that exists is automatically included in the definition of the universe.

Scientists do not know what came before the Big Bang. However, they do know that the singularity is not real; instead, it's an artifact of general relativity that occurs when the equations break down and lose their ability to describe a physical situation. A true explanation for the singularity must lie in a theory of quantum gravity, which is a physical theory of strong gravity at extremely tiny scales. Physicists do not currently have such a theory, but they do have several candidates, like string theory and loop quantum gravity.