How did the big bang happen? The word created is de facto because we have, in fact, been created.
The words you use are just words; just because you refer to something as having been "created" does not mean there is a "creator" responsible for it; it just means the particular language you're using is either insufficiently diverse enough to have a proper word for what actually happened, or the proper word is one you're not using for some reason.
As for how the big bang happened, the most common hypothesis is that the big bang resulted from random quantum fluctuation; no creator is necessary for this method and we know that it makes mathematical/physical sense for it to have happened this way. Do we know for certain? No. It is however, the only plausible explanation we have.
Correct, for some people at least. If we were pursue the science further, however, and attempt to use our method to explain how the universe got here, we quickly realize that neither God creating or "nothingness creating" can be scientifically tested.
Presently, this is true. However, this is irrelevant. The two are NOT on the same footing here. "God did it" is a non-scientific "explanation" that doesn't actually explain *anything*. You could replace 'god' with anything and the explanation wouldn't change. You could just as easily say the primordial carrot had a bad hairday and as a result cosmic bunnies started eating different foodstuffs instead, allowing the carrot to grow to such vast proportions that it started breaking down under its own weight, resulting in the big bang. It works out exactly the same as saying 'God did it'.
Science, on the other hand, comes up with explanations that while currently untestable, *do* in fact explain the how and why of the big bang. Furthermore, there is a non-zero chance that our technology might one day become advanced enough to test the hypothesis.
Neither atheism or theism is 100% scientifically testable, but one is more testable than the other.
The one that's testable is theism/creator-creation events. Scientists create this parallel lane of thinking every time they use the scientific method which implies (but does not confirm) intervention. An example would be creating a single celled organism, or any type of nuclear test.
Without anything, however, there is no test. Hence there is no testability. Hence one who somehow believes that all the results IMPLIED are somehow representative of the exact opposite of all the other implied test's conclusions relies on what I refer to as "super faith."
So a religious person, regardless of doctrine, relies on faith. A true atheist who honestly applies the scientific method to the universe's creation or even existence (and therefore cannot even have an entity present to conduct or even observe an allegorical test) relies on super faith.
You don't seem to understand the fundamental difference between theism and atheism then, or for that matter, the nature of 'faith'. Or you know, science. Atheism is simply the lack of belief in god. Whether or not it's 'testable' has no more relevance for atheists than for people (such as yourself, presumably) who do not believe in unicorns.
Faith is defined as the belief/trust in the absence of solid evidence or proof. By contrast, rejecting a belief in the absence of evidence either way, can by definition *not* be an example of faith (or 'super' faith).
Secondly, the scientific method does in fact have evidence as to the origin of the universe (there is overwhelming evidence that the big bang happened), and as for what caused it, there are at least plausible scientific hypotheses. Yes, these hypotheses are currently untestable. However, that is irrelevant since atheism itself doesn't concern itself with the topic to begin with, and irrelevant since atheists themselves who *do* concern themselves with it are generally not likely to *believe* (ie; have faith) these hypotheses to be true, but merely ascribe various degrees of probability to them. In other words, they can not be claimed to have 'faith' in any of it.