Well said, Álvaro :-). 知之為如知。不知為不知。是知也。Freely translated: to know when you do know something and when you don't know something, that's wisdom ;-).
The Big Bang itself stands on fairly firm ground, I believe ... it fits the data well and gives a good description of what is currently going on. As to what came before: any theory of the world that assumes a first origin leads to the immediate question: but what came before it? From that point of view, an infinite universe seems much more appealing, aesthetically. Whether it be an infinite series of contractions and expansions or a continuous expansion leading to near nothingness and a renewed expansion ex - quasi - nihilo, from a spontaneous bubble fluctuation?
Perhaps one day we will have a set of equations which will give a hint as to which model is more likely to be true. Radio waves "fell out" of Maxwell's equations before being practically observed, as did other phenomena which were first predicted from the model and later observed in nature. That is the power of mathematical models in physics. Until such day that we have such a comprehensive model, though, we must recognize that we simply do not know (yet). My 5c.