Formula to Calculate Baryon/Photon Ratio

Does anyone know how to derive the following formula?

Nb/Ny=(Omega-b*Ey)/(Omega-y*Eb)

Whe
Omega-b is Omega Baryon
Ey is the energy of a CMB photon = 2.7kT, where T=2.725
Omega-y is the ratio of CMB radiation density to the critical density
Eb=Mb*c^2, where Mb is the mass of a baryon


[[Mod. note -- This at least appears like it might be a university
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that (much) more information is generally imparted by general suggestions
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Dr Measle wrote in message ...
Does anyone know how to derive the following formula?

Nb/Ny=(Omega-b*Ey)/(Omega-y*Eb)


I didn't know there was a formula to calculate the baryon-to-photon
ratio?

At first I thought this was a hoax, but I tried it with the latest
WMAP data and got 6.13 +/- 0.27 x 10^-10 which matches their result
almost exactly. I also checked whether the baryon-to-photon ratio
changed as T and H changed, but they both scale accordingly (H^2
proportional to T^-3) to keep the ratio strongly conserved (as it
should be).

[[Mod. note -- This at least appears like it might be a university
homework problem.

Really? Who gave you the problem and where did they find it? Has
anyone else ever seen this formula, or is it just me?

Alastair

Dr Measle wrote in message ...
Does anyone know how to derive the following formula?

Nb/Ny=(Omega-b*Ey)/(Omega-y*Eb)


I didn't know there was a formula to calculate the baryon-to-photon
ratio?

At first I thought this was a hoax, but I tried it with the latest
WMAP data and got 6.13 +/- 0.27 x 10^-10 which matches their result
almost exactly. I also checked whether the baryon-to-photon ratio
changed as T and H changed, but they both scale accordingly (H^2
proportional to T^-3) to keep the ratio strongly conserved (as it
should be).

[[Mod. note -- This at least appears like it might be a university
homework problem.

Really? Who gave you the problem and where did they find it? Has
anyone else ever seen this formula, or is it just me?

Alastair