I am not a physics student, nor do I work in the field. I do however have a strong interest in understanding physics at a conceptual level (as in laymans explanations). I am struggling to understand/reconcile the idea that the universe began with the "big bang" (I understand this is not actually an accurate term) and has been expanding ever since. Given that as a accepted premise, my thinking goes to the the question of the limits of the universe. Assuming it (the universe) started out very small, a very large "space" must have existed within which the universe began to, and continues to expand. How is that "space" characterized ? Are there (proposed ?) theoretical limits to the future expansion of the universe based on any definition of the size of this original "space" within which it is housed ?