What did scientists use to come up with a theory about how the universe was created?

Scientists used their observations to come up with a theory about how the universe was created. More specifically, this theory is now known the big bang theory. According to the big bang theory, all matter in our known universe began as one tiny dot of matter, which then expanded at incredible speeds to form our universe, and is still expanding even today.

Sequoia national park  /  inyo national forest, california, u.s. mount whitney is the tallest mountain in california, as well as the highest summit in the contiguous united states and thesierra nevada—with an elevation of 14,505 feet (4,421 m).