What one thing would disprove Christianity to you?

[DoktorZ]

It's possible to define it,

True. I should have put it better. It's impossible to define if not in negative terms (absence of anything), so it's not a concept, but the absence of every concept.

Exactly ... I think.

The important point is that we don't have much in the way of empirical evidence from which to meaningfully discuss what a "nothing" would actually be. So, saying "nothing can't produce something" is an absolutely meaningless argument, because we don't have a nothing to examine.

Z