What kind of theory is a theory about the structure of the world? If by "the world" one wants to mean "everything", there is no such theory. Certainly, science has no such theory, nor could it have. "Everything" is not the name of one big thing or topic, and therefore, there can be no theory concerning a thing or topic of this kind. To speak of a thing is to acknowledge the existence of many things, since one can always be asked which thing one is referring to. Science is concerned with specific states of affairs, no matter how wide the scope of its questions may be. Whatever explanations it offers, further questions can be asked about them. It makes no sense to speak of a last answer in science, one that does not admit of any further questions. Science is not concerned with "the structure of the world", and there are no scientific investigations which have this as their subject.