# At the time of recombination, the mean temperature of the Universe was 3000 K.) Compute the energy density and pressure of the radiation b.

At the time of recombination, the mean temperature of the Universe was 3000 K.

a.) Compute the energy density and pressure of the radiation

b.) Assuming the velocity of the atomic particles can be described by a Maxwellian distribution, calculate the equation of state parameter, w, of the matter. Recall that the Universe is, to first order, 75% Hydrogen and 25% Helium.

c.) The matter density today is p = 3 x 10^-27 kg m^-3. Calculate the energy density and pressure of matter at the time of recombination. (Tcmb = 2.725 K today), where cmb is the cosmic microwave background.

d.) Is the acceleration of the Universe at recombination mainly due to matter or radiation? (show your work)

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