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Recently, Marco Ajello et al. (2018) has estimated the total number of photons in the whole observable universe as: $$N_\gamma \approx 4\cdot 10^{84}.$$ On the other hand, the ratio of baryons to photons or the baryon abundance is defined as: $$\eta \equiv \frac{N_b}{N_\gamma} \simeq 2.75 \times 10^{-8} \; \Omega{_b}h^2$$ being $\Omega{_b}h^2 = 0.0224 \pm 0.0001$ according to the Planck surveyor measures of 2018. All these numbers, suggest (if I am not confusing the data) that the total number of baryons in the universe is about:

$$N_b \approx 2.5\cdot 10^{75}.$$

Is this number in agreement with other experimental measures of baryonic abundance (I have not been able to find a suitable reference), already taking into account the missing baryon problem?

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The quantities considered in the question are not directly comparable. The Fermi collaboration (2018) measured the number of photons comprising the extragalactic background light, which is ultraviolet/visible/infrared light produced in galaxies. This is a tiny fraction of the total number of photons in the Universe, which is dominated by the cosmic microwave background (CMB). The photon-to-baryon ratio is the ratio between CMB photons and baryons.

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