We know that the universe was much denser and close together based on measurements, but cannot truly see the beginning. We think it’s most likely that the big moon in the sky most likely came from another planet hitting ours, but we don’t know exactly how the collision went down. Science is our best understanding, not some absolute source of knowledge. Our interpretations are often incorrect and updated accordingly, and even the most accurate theories are known to be an incomplete understanding. Until we understand everything, science is the search for knowledge, rather than knowledge itself.