What is the total number of protons in the observable universe? What's the total number of protons, is it equal to the number of electrons?
What is the Eddington number and how is it found?
 A: Well, one way to calculate proton amount in a universe would be :
$$ N_{\text{Edd}} = N_{\text{galaxies}} \,\cdot N_{\text{stars_per_galaxy}} \,\cdot \frac{M_{\text{star}}}{m_{h}}
$$
where $M_{star}$ is average star mass in a typical galaxy and $m_h$ is Hydrogen isotope $^1H$ mass.


*

*Galaxies in observable universe is about $2\cdot10^{12}$

*If we take our Milky Way galaxy as a reference, then stars in a galaxy would be $2\cdot10^{11}$ (lower bound)

*for typical star mass we can take our sun mass, which is $\approx 2\cdot 10^{30} \,kg$

*And most abundant Hydrogen isotope has mass of $1.7\cdot 10^{-27} \,kg$
Plunging all these numbers into formula gives us $\approx 10^{80}$ protons in a visible universe
EDIT
BTW, actual number should be somewhat bigger, because calculation not includes the amount of protons in : planets of universe, asteroids, comets, cosmic dust, etc. Also it is not known what happens to elementary particle when it falls towards singularity of a black hole. IF elementary particle, included proton, is not destroyed by singularity of black hole, then these calculations must include total number of protons existing in black holes of visible universe.
