Why does higher density of the early universe result in a faster expansion rate?

[lwymarie]

I heard from a TV program that higher density of the early universe resulted in a faster expansion rate, and the lower density of the present universe has a lower expansion rate. Could anyone please expalin to me why? Thanks =)

 

[sdemjanenko]

earlier when the universe was "smaller" and the amount of matter was the same or more ( some of the previous matter could have turned into energy). According to inflation theory which was devised to iron out some bugs in the previous theory the universe underwent a fast expansion. An expansion which has slowed. if the expansion is still slowing down then it must have been higher before, the ultimate expansion beginning with the big bang. Matter's graviational forces could slow down this expansion and are believed to have slowed it down in the past. Just in the past the rate of this slowdown was higher than it is now because they higher density meant a greater gravitational force per unit area, or volume than currently

 

[mathman]

Although right after the big bang there was this inflation period, where the universe expanded at an extremely raid rate, followed by a slowdown to "normal" expansion, at the present time the expansion rate is increasing.