I was talking to a friend, and she said: even before the Big Bang and the origin of space and time, still something existed.
That sparked the question: how would you define ‘existence’? What philosopher has found a formal definition?
Taking a Kantian view, of "interpreting existence as relation to the cognitive faculty", the nature of the existence of phenomena pre-dating any observer is inferred. That is to say, the existence of a Big Bang singularity is inferred, not a result of contemporaneous perception.
To elaborate on Kant's view, in the following quote Heidegger develops Thomas Aquinas' ontology through to Kant's.
Existere is something other than essence; it has its being on the basis of being caused by another. Omne quodest directe in praedicamento substantiae, compositum est saltem ex esse et quod est; [de Veritate 27 i Ans.8] each ens, therefore as ens creatum is a compositum ex esse et quod est, of existing and of whatness. This compositum is what it is, compositio realis; that is to say, correspondingly: the distinctio between essentia and existentia is a distinctio realis. Esse, or existere, is conceived of also, in distinction from quod est or esse quod, as esse quo or ens quo. The actuality of an actual being is something else of such a sort that it itself amounts to a res on its own account.
If we compare it with the Kantian thesis, the Thomistic thesis says - indeed, in agreement with Kant - that existence, there-being, actuality, is not a real predicate; it does not belong to the res of a thing but is nevertheless a res that is added on to the essentia. By means of his interpretation, on the other hand, Kant wishes to avoid conceiving of actuality, existence, itself as a res; he does this by interpreting existence as relation to the cognitive faculty, hence treating perception as position.
Etymologically speaking, existence is defined as:
the fact or state of living or having objective reality.
But that doesn't even begin to cover your question because two instant follow-ups to that definition is "what is objective reality" and "how do we know it's true".
So to stick to your question, physicists state that talking about before the Big Bang is nonsensical. At least with our current understanding of physics. Reason being that time as we know it began with the big bang. So to say that something existed before it, is equal to saying "time before there was time".
In addition, existence as we currently understand it is thought of as temporal. So unless there was some different kind of time before our time, there could be no existence before the Big Bang.
Does that make any sense?