Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Joe L. Ogan on 19/06/2013 20:45:00

Title: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: Joe L. Ogan on 19/06/2013 20:45:00
Assuming the universe was the shape of a ball, how large was it when the Big Bang happened.  Thanks for comments.  Joe L. Ogan
Title: Re: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: syhprum on 20/06/2013 08:37:44
The usually quoted figure for the mass of the observable universe is 6*10^51 kg assuming the universe was compressed to Planck density 5.1*10^96 kg/m^3 then it could be contained in a cube of side approximately 1.176*10^-15m or a sphere of 0.654*10^-15m radius.
Title: Re: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: evan_au on 22/06/2013 11:04:12
Assuming that there has been no fundamental change in the laws of physics, the universe with this density would have formed a black hole with a Schwarzschild radius of about 1025 meters (about 10 light-years).

The Schwarzschild radius (https://en.wikipedia.org/wiki/Schwarzschild_radius#Parameters) of a black hole rs = 2GM/c2
Where
Title: Re: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: Pr. snoerkel on 22/06/2013 12:40:20
I have been using the same argument to speculate that the big bang could not have happened that way. But now I am not so sure. My thinking is like this:
 Assuming that the Universe started off having no mass (because it contained nothing but photons without rest mass), then - when matter formed - the size of the universe would be considerable. Gravity would only come into being then, and since the gravity could only radiate with the speed of light, it would take some time for any particle to "feel" the effect of the rest of the matter. In the meantime the matter would continue to move away from the center of the big bang at near light speed.
Is it possible that once a particle is affected by the full force of the rest of the matter, it is already far beyond the Schwarzchild radius?
Title: Re: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: Bill S on 22/06/2013 19:44:26
A couple of questions come to mind, here.

1. Does a hole not have to be a hole in something?  If the Universe is all there is, in what could it be a hole (black or otherwise)?

2.  If there is no space outside the Universe, where (and what) would the Schwarzschild radius be? 
Title: Re: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: Pr. snoerkel on 23/06/2013 10:57:43
Quote from: Bill S on 22/06/2013 19:44:26

1. Does a hole not have to be a hole in something?  If the Universe is all there is, in what could it be a hole (black or otherwise)?

2.  If there is no space outside the Universe, where (and what) would the Schwarzschild radius be? 

I suppose that is right. If you cannot be outside a hole, is it a hole then? But that is metaphysics. From inside the hole it does not matter what, if anything, is outside. The characteristics of the hole is - according to science -that everything is located in a singularity. That is not what we see, so we conclude we are not inside a black hole.
Title: Re: Assuming the universe was the shape of a ball, how large was it when the Big Ban
Post by: lean bean on 23/06/2013 13:04:27
Quote from: Joe L. Ogan on 19/06/2013 20:45:00
Assuming the universe was the shape of a ball, how large was it when the Big Bang happened.  Thanks for comments.  Joe L. Ogan

Joe
 You may be interested in this old web page…

Quote
The Universe was not concentrated into a point at the time of the Big Bang. But the observable Universe was concentrated into a point.

From  http://www.astro.ucla.edu/~wright/infpoint.html