# How many protons in the known universe

Alcra
Posers and Puzzles 31 Mar '06 07:07
1. Alcra
Lazy Sod
31 Mar '06 07:07
Can the number of protons in the known universe be estimated? If so, what is the estimate, and how did you derive the answer?

Along the same lines, what is the total area of the known universe?
2. 31 Mar '06 08:01
Originally posted by Alcra
Can the number of protons in the known universe be estimated? If so, what is the estimate, and how did you derive the answer?

Along the same lines, what is the total area of the known universe?
Well, you say the known universe and that makes the answer quite easy.
We know the mean density of the universe, including the almost empty intergalactic space. The very most of the matter (including protons) are concentrated in stars and the stars are easaly seen. Radio observations detect (more or less) cold matters between stars. And these observations supports observational data about intergravitational forces.
So, yes, the number of protons are quite easy to calculate.

When you ask about area (two-dimensional) in the space (three-dimensional) there can be no answer. The question is not well defined.
3. sonhouse
Fast and Curious
31 Mar '06 15:31
Originally posted by FabianFnas
Well, you say the known universe and that makes the answer quite easy.
We know the mean density of the universe, including the almost empty intergalactic space. The very most of the matter (including protons) are concentrated in stars and the stars are easaly seen. Radio observations detect (more or less) cold matters between stars. And these observation ...[text shortened]... onal) in the space (three-dimensional) there can be no answer. The question is not well defined.
I think he meant the total 'volume' of the universe, which of course changes from second to second but you can build up a good picture of it anyway.
4. 31 Mar '06 16:37
Originally posted by sonhouse
I think he meant the total 'volume' of the universe, which of course changes from second to second but you can build up a good picture of it anyway.
Is it agreed on whether the universe is considered being infinite or not yet? I don’t think so.

If the Universe is infinite, then the question has no meaning.
If he just mean the known universe, his question is answerable.
And he actually wrote “the known universe”.

If the size of the universe is expanding doesn’t alter the answer. There is no more protons than before, only less in density.
5. 02 Apr '06 03:04
There are four protons in the universe.
6. 02 Apr '06 15:10
Originally posted by Drumbo
There are four protons in the universe.
It's more than that - now.
7. Bowmann
Non-Subscriber
02 Apr '06 19:04
Probably too many.
8. Alcra
Lazy Sod
03 Apr '06 06:18
Originally posted by sonhouse
I think he meant the total 'volume' of the universe, which of course changes from second to second but you can build up a good picture of it anyway.
Yeah, thanks. I meant volume.
Also, even though the universe is expanding, its present size is so large that the tiny (relative) expansion it has undergone since posing this question would be negligible.

My thoughts on its volume are as follows:
Take the age of the universe as 15 billion years. Take the speed of light as c and the distance light travels in one year as C. Then, the radius of the universe would be 15 billion * C kms, and the volume can be calculated form that.

As for protons, I come out at around 2*10E79 protons - but am unsure as to the validity of that. Working,
Mass of the sun in kgs around 2 * 10^30 kgs = x
mass of proton = 1.67 * 10^-27 kgs = y
protons in the sun = x / y = 1.20E+57

Since the sun is thought to be 1/100 billion of the mass of the galaxy, then protons in the galaxy = 1.20E+68

Assumptions on the number of galaxies is 200 billion, so
2.40E+79 protons

Now, of course the sun also contains neutrons and electrons. I thought I can safely dismiss the electrons as they are much less massive than protons, but what is the distribution of neutrons to protons.
Also, what about interstellar gas - would that make a perceptible difference to my assumptions?
9. 11 Apr '06 09:13
Originally posted by FabianFnas

... There is no more protons than before, only less in density.
This is untrue, matter is constantly being created and destroyed contraty to popular belief but if you've heard the equation e=mc^2 then you should already know that.
10. 11 Apr '06 09:211 edit
Originally posted by MarsII
This is untrue, matter is constantly being created and destroyed contraty to popular belief but if you've heard the equation e=mc^2 then you should already know that.
Matter converts to energy in stars center, that's right.
But where is energy converted to matter (aside at the Big Bang itself)?

Okay, at the center of Supernovas, but it's not really that much c
compared at the whole...
We have no equilibrium at all between creation of matter from energy and creation of energy from matter.

Does it matter, anyway?
11. XanthosNZ
Cancerous Bus Crash
11 Apr '06 09:37
Originally posted by FabianFnas

Does it matter, anyway?
You stated that the number of protons in the universe is a constant and now you're saying that no it isn't?
12. 11 Apr '06 09:571 edit
Originally posted by XanthosNZ
You stated that the number of protons in the universe is a constant and now you're saying that no it isn't?
Sorry for the joke about matter and energy - "Does it matter?"

In the stars fusion process, it doesn’t consume nor produce protons.
In a supernova, it doesn’t consume nor produce protons.
(As far as I know.)

But when matter is pressed together in neutron stars or black holes - protons are consumed and neutrons produced.

What other processes consume or produce protons in an amount that is considerable? The expansion of universe doesn't produce nor consume protons though.
13. sven1000
Astrophysicist
12 Apr '06 01:231 edit
The expansion of the universe does not create protons, but the number in the "known" universe still increases, because the volume of the universe we can see increases. As time goes on, we see more of the previously "unknown" universe, which of course has protons, neutrons, and everything else in it as well. Thus the two questions are actually tied together, since the number of protons depends on the volume of space we can see. The average density of the universe is about 7.5 x 10^-31 g/cm^3 and about 7/8 of that is in protons (mass = 1.67x10^-24 g). The volume of the universe is about 4*pi*(c*age)^3/3 = 9 x 10^84 cm^3. So the number of protons (currently) is roughly 3.5 x 10^78.
14. 12 Apr '06 11:25
Originally posted by sven1000
... The volume of the universe is about 4*pi*(c*age)^3/3 = 9 x 10^84 cm^3. ...
When you apply a formula for calculating tha volume to a such large entity as the known univers itself, you have to take the topology of the universe into consideration. Is our universe open or closed? Is it spherical, hyperbolical or straight up flat? Do you know? Does anyone know? Yet?
15. Alcra
Lazy Sod
12 Apr '06 12:12
Originally posted by sven1000
The expansion of the universe does not create protons, but the number in the "known" universe still increases, because the volume of the universe we can see increases. As time goes on, we see more of the previously "unknown" universe, which of course has protons, neutrons, and everything else in it as well. Thus the two questions are actually tied togethe ...[text shortened]... *(c*age)^3/3 = 9 x 10^84 cm^3. So the number of protons (currently) is roughly 3.5 x 10^78.
OK, we have come pretty close to each other, using two different techniques.

Any other ideas?