It wouldn't, that's the point. The is no need for a "notion of nothingness" if nothing exists.
Why do you think nothingness doesnt't make any sense? It's a simple concept: no space, no time, and therefore nothing else such as matter, etc.
> how would something even start to exist?
Perhaps it wouldn't. We weren't talking about the origin of the universe from nothing. If you want to say existence is irrefutable because we observe it, that's fine. But it's not irrefutable because of its definition, that's religious circular logic, like the ontological argument.
