Is the Scope of the Causal Principle Metaphysical?

I think that when somebody objects to the causal principle by saying, you know, this is something that applies to things within the universe, that what they're doing there is challenging the assumption that the scope of the causal principle is in fact metaphysical and not physical. So I think it does not good to respond to that objection by reasserting the very thing being questioned, which is that thescope of the causal Principle is metaphysics. That sounds question begging to me. After all, we've only experienced with ... things within the universes anyway.