Before the Big Bang, there was a state of incredibly high energy and temperature known as the singularity. This singularity is considered the starting point of the universe, and it is believed to have contained all the matter and energy that would eventually form the cosmos.

The Big Bang theory describes the rapid expansion of the universe from this singularity, during which the universe underwent a phase transition and the fundamental particles and forces that govern our universe were formed. As the universe expanded and cooled, galaxies, stars, and other cosmic structures began to form through gravitational interactions.

It's important to note that the exact nature of what existed before the Big Bang is still a topic of ongoing scientific research and debate. Some theories propose that the universe was in a state of quantum fluctuation or a multiverse before the Big Bang occurred. However, due to the limitations of our current scientific knowledge and observational capabilities, the exact details of what preceded the Big Bang remain speculative.