Well first, a theory means a well-substantiated body of facts, evidence, predictions, and explanations. For example, gravity remains a theory. There is nothing to prove that it won't suddenly stop working, or start working in reverse.
Second, existence could theoretically exist without the Big Bang. Before the Big Bang, there was allegedly an infinitely dense mass of matter. This existed, yet it was still before the Big Bang.
Second, existence could theoretically exist without the Big Bang. Before the Big Bang, there was allegedly an infinitely dense mass of matter. This existed, yet it was still before the Big Bang.




