What is the mass of all photons emitted in the universe since the Big Bang?
I think the OP wanted a big number. This tidbit fulfills that I believe.... according to the new measurement, the number of photons (particles of visible light) that escaped into space after being emitted by stars translates to 4x1084
That's the mass of each individual photon, but I think the OP reather asks for the total mass of all photons.
This actually raises all sorts of complications. The answer I gave in post #2 is really the answer to the question "What is the sum of all the the masses of photons emitted since the Big Bang?" But in relativity, the mass of a collection of particles is not necessarily equal to the sum of the masses of each particle. In special relativity, a collection of photons has a non-zero mass, unless all the photons travel in the same direction. In general relativity, the mass of a system isn't a well-defined concept. There are a number of different types of system mass, and some of them make sense only in special circumstances.Isn't n times Zero still zero?
So zero times infinity?That's the mass of each individual photon, but I think the OP reather asks for the total mass of all photons.
No, it isn't (not only in this special case). Better get the total energy E and the total momentum p of all potons and calculate the total mass according to E²=m²+p² (with c=1).So zero times infinity?
That's the trivial case. Reading "universe" as the visible universe is more challenging.If the universe is both homogenous and infinite (both of which we assume) then the total number of photons is infinity, and has been since the electroweak epoch.
Then you don't need or want the additional complication of integrating over the entire universe. The photon density is enough to compare. It's something like 10-5 of the total density.I wanted to see how it matched up to the amount of "dark matter" or "dark energy" in the universe.
It seems the term "photon" caused a lot of confusion. I think what you actually mean is the total radiation field.4*1084*Percentage of photons still traveling in space (gotta be close to unity)* mass of photon traveling in space. I wanted to see how it matched up to the amount of "dark matter" or "dark energy" in the universe.