human
Can you explain what the 'big bang' is?
assistant
The Big Bang theory states that the universe began as a hot, dense and rapidly expanding state approximately 13.8 billion years ago. This event was so powerful that it caused the universe to expand at an ever-increasing rate. The Big Bang theory is supported by scientific evidence such as the cosmic microwave background radiation, which is the oldest light in the universe, and the abundance of light elements like helium and hydrogen.