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Question
The peak intensity of the CMBR occurs at a wavelength of 1.1 mm. (a) What is the energy in eV of a 1.1-mm photon? (b) There are approximately $10^9$ photons for each massive particle in deep space. Calculate the energy of $10^9$ such photons. (c) If the average massive particle in space has a mass half that of a proton, what energy would be created by converting its mass to energy? (d) Does this imply that space is “matter dominated”? Explain briefly.
1. $1.1\times 10^{-3}\textrm{ eV}$
2. $1\textrm{ MeV}$
3. $5\times 10^{2}\textrm{ MeV}$
4. Space is matter dominated since the energy accounted for by matter is greater than that of photons by a factor of ~500.
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