This has likely been asked before but my attempts at searches did not yield what I was looking for. Assuming the universe is perfectly flat (so far that seems very possible), what are the ramifications? Such as to: 1) Inflation 2) Dark Matter 3) Dark Energy 4) Nature of Gravity 5) Applicability of General Relativity to the Cosmological Problem Much of the above all seem to be intertwined with the use of General Relativity AND the assumption that gravitational force is acting on the universe as a whole (in what seems to be the 'time coordinate' or directly related to it). It would seem that a perfectly flat universe would not need GR. It could be possibly be more simply explained as an initial 'big bang' with the 'pieces' (our universe) being expelled at a constant velocity (less than the speed of light?). It is my understanding of the other forces that a 'transport particle' can be used to describe how the forces come about. For the electromagnetic force (in QED) these are photons (with spin-like properties), etc. For gravity a 'graviton' has been proposed (a zero rest mass -- speed of light particle). This is one factor that I understood to mean that something like 'inflation' was needed in order to get around the 'horizon' problem -- one related to a finite transport velocity. The arguments for dark matter and dark energy were also based on the view that gravity effects need to be 'balanced' in various ways. But if there were no gravity effects at the very large cosmology scale -- would all this still be needed? If still needed, then in what way ... how changed? Likely someone has recently put out a book on all this (too obvious not to) -- but what is a good one? Or is that too early to tell too. I seems to me that a known 'flat universe' -- and if assumed to be the normal stable condition -- puts many assumptions in jeopardy.