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Cosmological solutions of the Einstein-Friedmann equations ...

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Cosmology<br />

(in accord with <strong>the</strong> universal behavior just mentioned before):<br />

i.e.<br />

˙S 2<br />

¯C<br />

→<br />

c2 S<br />

2 or<br />

˙S 2<br />

S 2 → c2 ¯C<br />

S 4 = c2 κρ<br />

3<br />

ρ(t) = ρEdS(t) = 3<br />

κ<br />

H 2 (t)<br />

c 2 .<br />

In fact <strong>the</strong> observed energy density at present is close to <strong>the</strong> critical one. This we<br />

will discuss later. Even if one counts <strong>the</strong> normal baryonic matter only one is not<br />

much more than a factor <strong>of</strong> 10 <strong>of</strong>f from <strong>the</strong> critical value Ω = 1 (atoms ∼ 4%) . The<br />

c○ 2009, F. Jegerlehner ≪❘ Lect. 7 ❘≫ 476

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