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Radiation question

  1. Dec 11, 2007 #1
    Hey guys, can someone please help with this question.

    We now live in a time when the energy balance of the universe is dominated
    by Λ. A long time from now, at t2× the universe will have doubled
    in size, i.e.: a(t2×) = 2. At present, radiation is negligible: Ωr,0 ~ 0,
    and will remain so, while Ωm,0 = 0.3 and ΩΛ,0 = 0.7 now. Note that
    since ΩΛ,0 + m,0 = 1 now, their sum will remain the same.
    a) Estimate the value of Ωm at t2×. Consider how the ratio Ωm/ΩΛ
    changes with time, and use the flatness constraint mentioned above.
    b) Estimate the time from now until t2×.
    c) What will the Hubble distance be at t2×?
  2. jcsd
  3. Dec 11, 2007 #2

    George Jones

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    Can you express

    [tex]\frac{\Omega_m \left( t \right)}{\Omega_\Lambda \left( t \right)}[/tex]

    in terms of


    and [itex]a \left( t \right)[/itex]?
  4. Dec 11, 2007 #3
    Yeah it can be expressed like that
  5. Dec 12, 2007 #4

    George Jones

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    This with [itex]a \left( t \right) = 2[/itex] and [itex]\Omega_\Lambda \left( t \right) + \Omega_m \left( t \right) = 1[/itex] give two equations with two unknowns.

    For part b), integrate the Friedmann equation.
  6. Dec 13, 2007 #5
    Thnx George that realy helped, but can you please give more details ?
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