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# Accelera8ng constant speed 2 3 decelera8ng 53013

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Unformatted text preview: 1,\$so dz / dt = −H / a = −H(1 + z),\$so dz dt = − H(1 + z) •  Thus the lookback 8me is: t0 ∫ dt = te 5/30/13 z ∫ 0 dz" 1 ≈ H(z")(1 + z") H0 z ∫ 0 dz" (1 + z") Ωm ,0 (1 + z")3 + ΩΛ ,0 UW, ASTR 323, SP13, Eric Agol ©2013 4 Three cars are going exactly the same speed now Which one took the longest to go from the ﬁrst line to the second? accelera8ng constant speed 2 3 decelera8ng 5/30/13 UW, ASTR 323, SP13, Eric Agol ©2013 5 The age of the Universe & dark energy: •  Higher ma]er density takes less 8me to decelerate •  Ma]er density (ρ=0.315ρcrit) alone would imply the Universe is 11.2 Gyr old (open) •  But, oldest globular clusters: 11.5 Gyr •  Adding dark energy gives an age of 13.8 Gyr •  This was taken as an indica8on for evidence of dark energy, but it was not convincing un8l s...
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