[Dalewyn]

Something that intrudes upon this universe from another universe, perhaps.

Nothing that is a product of this universe, whether directly or indirectly, is unnatural. Everything is natural, from steel skyscrapers to beaver dams to beehives to planets and stars.

[dTal]

Clearly "natural" and "unnatural" denote categories that it is useful to distinguish between, or we would not have the words. What is to be accomplished by your attempt to redefine the concept into uselessness, apart from making it difficult to discuss environmental issues?