"There is nothing outside this experience."

A thought.

"There is something outside this experience."

Another thought.

Clearly, if there is anything outside this experience, it cannot be known from inside this experience. If something that was outside this experience enters this experience, it's no longer outside and it becomes known. But there's no way to know whether it existed before entering this experience or whether it came into existence at the point of entering this experience.

All that can be known from within this experience is this experience and its contents -- the awareness which contains and supports it, the forms (thoughts, perceptions, sensations, emotions) that come and go within and as the awareness.

I'm not in a position to say that there is nothing outside this experience, but if there is something beyond this experience, I'm also not in a position to say what it might be. In essence, there's nothing I can say about it.