Implications of Slowing Expansion Rate
• Our calculation of age T=1/Ho = 13.6 billion years assumed constant rate
• Gravity should slow the expansion rate over time
– If density is high enough, expansion should turn around
• If expansion was faster in past, it took less time to get to present size
• For “Flat” universe  T = 2/3 * (1/Ho) = 9.3 billion years
– contradiction with other ages if T is too small