The concept of what existed before the Big Bang is still a topic of scientific inquiry and speculation. The Big Bang theory describes the expansion of the universe from a highly dense and hot state, but it doesn't address what caused the initial singularity or what existed before it.
According to current scientific understanding, the laws of physics, as we know them, break down at the moment of the singularity. Therefore, it is difficult to make definitive statements about what caused the Big Bang or what might have existed before it. The nature of time and causality may be different or incomprehensible in such extreme conditions.
Speculative theories and hypotheses such as the cyclic model or multiverse theories propose the existence of other universes or cycles of expansion and contraction, but these ideas are still being explored and are far from being proven.
In summary, the question of what caused the Big Bang or what existed before it remains a topic of active scientific research, and currently, we do not have a definitive answer.