The question "What existed before the Big Bang?" is often considered problematic because it assumes that there was a "before" the Big Bang, as if time and space existed prior to the Big Bang event. However, according to our current understanding of cosmology, the Big Bang represents the beginning of both space and time. Therefore, asking what existed before the Big Bang is akin to asking what is north of the North Pole or what happened before time began—it seems to involve a logical contradiction.
The concept of time as we understand it breaks down at the moment of the Big Bang. Time is thought to have emerged as a property of the universe following this event. Prior to the Big Bang, there is no framework within which we can meaningfully discuss "before" or "existence" in the conventional sense.
Additionally, our scientific models and theories cannot currently describe or explain the exact nature of the universe at the moment of the Big Bang. Our understanding of the universe becomes less reliable and more speculative as we approach the singularity, the point of infinite density and temperature. This lack of knowledge further contributes to the difficulty in addressing what might have existed before the Big Bang.
In summary, the question assumes the existence of time and a pre-existing state, which may not be applicable before the Big Bang. The current understanding of cosmology suggests that the concept of "before" may not have any meaning in the context of the Big Bang.