Wow, I see you replied three years ago and I missed it!
I'm much better at catching replies now, sorry.
I do want to correct you on one thing - no one's postulating that at the hypothetical big bang, nothing turned into something. We literally have no idea what could have happened before it.
Yes, I agree with you that we cannot be certain that the big bang happened. But we cannot be certain of pretty well anything we have not directly experienced ourselves. Did Alexander the Great exist? Lots of evidence but it's hearsay. What about Lincoln? Same story. It's very very hard to believe that all the evidence about Lincoln is faked but we can't actually rule it out.
Over the last century, there has been an immense amount of evidence collected about the existence of the big bang. And yes, this is complexified by the fact that specialists are gathering that evidence, and it is not comprehensible to your average audience. But the same is true about evidence of the existence of Alexander the Great.
So I I "know" that the Big Bang happened in a similar way that I "know" that Alexander the Great existed. I can follow the ideas behind the argument in both cases, I believe that if I spent the years it would take to become an expert on these matters that I would agree with the academics on this matter.
I don't "know" it in quite the same way I know there is someone watering outside this window, but it is a valid usage of the word "know".