I'm coming with a good background in Big Bang expansion as the following sci-am article shows (which I've mastered): http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.pdf [Broken] What I'd like to understand is this. Expansion can only be felt in unbound system. Meaning brooklyn doesn't expand because matter are bounded with one another. But in depth of space in between super galactic clusters where there are no matters. Space expand. Can we say the space there is Minkowski flat (since there is no matter to cause spacetime curvature)? If so.. then this minkowski flat space is expanding? But they said space expansion automatically means curve spacetime. Is this true? There seems to be some contradictions. Can anyone help clear up this confusion? Thanks.