Consider a 2-dimensional spacetime. For a 3-, let alone a 4-dimensional spacetime it's impossible to envision the curvature of spacetime near (at the beginning or just after) the big bang.
Is it possible though to show a picture of a 2-dimensional highly curved spacetime (which maybe can't exist but which is used here only to make the 4d case clearer) near the big bang (in a 1d space) using a second space dimension? It would make the 4d case much more intuïtive. If so, what would it look like? Of course, also QM has to be taken into account in this regime according to mainstream physics stories, but until now, there is no guarantee (but a plethora of theories trying to match general relativity with QM: look here) that QM is applicable to spacetime like it is to the three fundamental forces (the weak, strong and e.m. force).