Final answer:
According to the Big Bang Theory, the universe didn't always look the way it does now. It began as a singularity and rapidly expanded in an event called the Big Bang about 13.8 billion years ago.
Step-by-step explanation:
According to the Big Bang Theory, the universe didn't always look the way it does now. The theory suggests that the universe began as a singularity, a point of infinite density and temperature, about 13.8 billion years ago. It then rapidly expanded in an event called the Big Bang, and has been expanding ever since. This expansion is supported by observations of the redshift of light from distant galaxies and the cosmic microwave background radiation.