In modern cosmology, it is commonly stated to the public that as we look deeper and deeper into space, we are seeing further into the past. CMB is the relic of the big bang after photon decoupling following recombination. However, if we pushed further back in our conceptualization, eventually we get to the period of inflation, and then to a period before that where energy density of the universe was some large value (possibly infinite).
So why would it be wrong to conceptualize the universe as being enclosed by an infinitely dense shell?
Update: For clarification, wikipedia has a good definition of observable universe, and answers in the affirmative on how every observer will see a different observable universe. This question is whether there are valid approaches in theories to avoid issues of big bang singularites.
Update2: I scaled back the question and accepted an answer, I think I was being overly vague in the write up and plan on asking the question again.