What is the mass of all photons emitted in the universe?

In summary, the mass of all photons emitted in the universe since the Big Bang is approximately ##7.107 x 1030 kg##.
  • #1
Louis Nardozi
2
0
What is the mass of all photons emitted in the universe since the Big Bang?
 
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  • #2
Louis Nardozi said:
What is the mass of all photons emitted in the universe since the Big Bang?
Zero

See our FAQ: Do Photons have Mass?
 
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  • #3
DrGreg said:
Zero

That's the mass of each individual photon, but I think the OP reather asks for the total mass of all photons.
 
  • #4
Isn't n times Zero still zero?
 
  • #5
sophiecentaur said:
Isn't n times Zero still zero?
It is.
 
  • #6
Let's try this phys.org precis of a paper that estimated all of the starlight in the visible universe since "time zero":
https://phys.org/news/2018-11-scientists-starlight-universe.html
... 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

I think the OP wanted a big number. This tidbit fulfills that I believe.
 
  • #7
DrStupid said:
That's the mass of each individual photon, but I think the OP reather asks for the total mass of all photons.
sophiecentaur said:
Isn't n times Zero still zero?
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.

The original question asked about all photons emitted throughout the duration of the Universe, and they cannot be considered as a system of particles with a system mass, as photons are being created and destroyed all the time. Even if the question was changed to refer to all photons in existence now (whatever "now" is interpreted to mean), it still doesn't make much sense, I think, to talk about system mass as the photons don't form an isolated system: they are interacting with other particles.

So I think the best answer is ##4 \times 10^{84} \times 0 = 0##.
 
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  • #8
DrStupid said:
That's the mass of each individual photon, but I think the OP reather asks for the total mass of all photons.
So zero times infinity?Also, isn't the "number of anything in the universe" entirely non-sensical? 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. Before which the number was exactly zero.
 
  • #9
newjerseyrunner said:
So zero times infinity?

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).

newjerseyrunner said:
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.

That's the trivial case. Reading "universe" as the visible universe is more challenging.
 
  • #10
newjerseyrunner said:
So zero times infinity?
##10^{84}## is a fairly large number, but it's still a finite number.
 
  • #11
I was looking for something along the lines of:

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.
 
  • #12
OTOH, a sharp upper limit on a photon's mass, 1.77 x 10-54 kg, times 4 x 1084, gives 7.107 x 1030 kg. A few solar masses, eh?:smile:
 
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  • #13
Louis Nardozi said:
I wanted to see how it matched up to the amount of "dark matter" or "dark energy" in the universe.

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.
 
  • #14
Louis Nardozi said:
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.

It seems the term "photon" caused a lot of confusion. I think what you actually mean is the total radiation field.
 

1. What is the definition of mass in the context of photons?

In the context of photons, mass refers to the amount of energy that a photon possesses. Unlike traditional particles, photons do not have a rest mass, but they do have a relativistic mass which is determined by their energy and momentum.

2. How is the mass of photons calculated?

The mass of photons can be calculated using Einstein's famous equation, E=mc2, where E represents the energy of the photon and c represents the speed of light. This equation shows that mass and energy are equivalent, and the mass of a photon is directly proportional to its energy.

3. What is the total mass of all the photons emitted in the universe?

The total mass of all the photons emitted in the universe is estimated to be around 4 x 1048 kg. This may seem like a large number, but in comparison to the total mass of the universe (around 1053 kg), it is relatively small.

4. How do photons contribute to the overall mass of the universe?

While photons do have mass, they make up a very small percentage of the total mass of the universe. The majority of the mass in the universe is made up of dark matter and dark energy, with regular matter (including photons) making up only about 5% of the total mass.

5. Can the mass of photons be measured directly?

No, the mass of photons cannot be measured directly. This is because photons do not have a rest mass and therefore cannot be weighed like traditional particles. However, their energy and momentum can be measured, and from this, their mass can be calculated using the equation E=mc2.

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