Hi there. I'm having a hard time understanding the precise meaning of the so called "cosmological principle": My understanding of the general Big-Bang model is that far enough back in time the observable universe came down to something very small (compared to now), very dense, very hot... Ok, i would have other questions about that but it's not the topic here. So, the next picture is one of this "small" universe spreading incredibly, part of which probably due to inflation (but maybe not?), the other part comparable to the way a gas concentrated in a small region would rapidly spread due to random motion of its particles. Now in this picture i don't see how to justify the assumption of homogeneity throughout all space: it seems that there is a natural, effective center of momentum in the universe and we can expect homogeneity at a given radius from this center (in terms of matter density and therefore metric as well), and also isotropy with respect to this center, but certainly not for any arbitrary point in the observable universe... Also, say we're standing at the edge of this universe: there's certainly no sense of homogeneity and isotropy so what is wrong with my understanding, please? This might be very basic but i doubt i'm the only beginner in Cosmology who doesn't understand it... Thanks!