Within the big bang theory, how can I conceptually understand the needing for an inflationary expansion? Why the CMB should be different than the observed one without inflation? Really the concept please.
PS in case the requirement is due to the cosmological principle. In this case I understand that if I have to see the same CMB every where ( say outside our observable universe or even inside but being at midway ) then inflation is necessary. To clarify what I mean here: with the same thinking, strictly applying the cosmological principle tell me that the universe is spatially infinite ( especially if curvature is , as it seems, quite unity) .