While I think I understand the general principle behind CMB and blackbody radiation, I am trying to understand whether it directly supports the current assumptions about age and size of the universe. Therefore, I was hoping that some members of this forum might be able to clarify what basic implications are being drawn from the Cosmologic Microwave Background (CMB) in respect to verifying the current accepted cosmological model. Apologises for the number of initial questions, but it was difficult to separate out the dependencies of the issues. For this reason I have numbered the questions so each may be addressed separately. Would appreciate any clarification of any issue. ----------------------------------- 1) As I understand the issue, we can measure the energy of CMB across its wavelength distribution, i.e. a black body distribution. The essence of the Penzias and Wilson discovery, in 1965, being that this distribution has a peak at a wavelength corresponding to 1.869mm in the microwave spectrum? 2) Is this peak wavelength then used to calculate the much-quoted CMB temperature of 2.7K via Wien’s Law? From my reading of the accepted cosmological model, the CMB is said to be associated with the decoupling of photons and normal matter. This being a point in the expansion of the universe where the temperature falls below 3000K some 379,000 years after the Big Bang. Again, as I have understood this process, this is a temperature below which photons no longer have the energy to maintain the ionisation of hydrogen as a plasma. What surprised me was the apparent accuracy of the time this is said to have taken place. 3) Presumably, based on Planck equation E=hf, you can work out the frequency-wavelength of photons that would have enough energy to maintain the plasma state from which I am assuming you can also determine the temperature, e.g. 3000K. However, I don’t understand how this tells you anything about how long ago it took place? 4) As a general statement, is it true that basic age and size estimates are still essentially based on the Friedmann equation, allied with the Fluid and Acceleration equations, inserting the measurement of the Hubble constant (H) and the current homogeneous density of the universe? 5) If so, is it fair to say that CMB is useful as a verification data point, but does not directly confirm the age or size of the universe?