Hi, I'm totally lost on how inflation solves the horizon and flatness problem. Flatness Problem Explanation I have d/dt(1/Ha)<0 and therefore [itex] |\Omega-1| [/itex] is driven towards zero rather than away from it. My Confusion Doesn't inflation increase the volume of the universe, and hence wouldn't the density decrease rather than increase? Or am I misunderstanding the density parameter here? Horizon Problem Explanation I have The quantity 1/Ha is the comoving Hubble length, and determines which two regions can communicate now. The particle horizon on the other hand, separates two regions that could never have communicated. The horizon problem is solved by the possibility of greatly reducing the comoving Hubble length. Hence, regions that cannot communicate today were in causal contact early. My Understanding The way I understand this is that, the comoving Hubble length gets smaller with time. Therefore region that were within the comoving Hubble length earlier and hence could communicate and affect each other, are now out of contact. So even though we look at space and see regions that can't communicate now, there was a time when they could do so. Does what I have just said make sense? My Confusion Finally my question on this part is, how does the particle horizon bit come into the picture? Can someone try and explain?