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
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?