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The Observed Universe, Our Universe, Our Big Bang.



 
 
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  #21  
Old July 19th 14, 03:27 PM posted to sci.astro.research
Nicolaas Vroom
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Posts: 216
Default The Observed Universe, Our Universe, Our Big Bang.

Op dinsdag 15 juli 2014 09:37:24 UTC+2 schreef Phillip Helbig:
In article , Nicolaas Vroom

writes:

The question is: are "Our observable Universe" and "all what is
created as a result of the Big Bang" identical concepts


No. The former is the observable universe and the latter the universe.
Or, in Tegmark's terminology, the former is the universe and the latter
is the Level I multiverse.


The issue is that IMO our primarily interest should be in what you call
"the universe". I would call that "Our universe" created by "Our Big Bang"
completely indepent of any human "behaviour".
The word "our" is only there to allow for more Big Bangs.

Accordingly to Tegmark at page 121:
As we saw inflation predits that there is even more.


By this he means that inflation predicts that the universe is much
larger than the observable universe, perhaps infinitely larger. By
"simplest example" he means what he calls the Level I multiverse.


What I understand is that before inflation the observable universe
was small and equally in size as the (our) universe but after inflation
the (our) universe became much larger as the observable universe.
If that picture is correct it makes sense to first study the larger
part.
The question arises where is this larger part?
before the CMB radiation or after the CMB radiation?
(relevant to our position)


what the simulation shows that in general in the early universe the
density is always close to the critical density and that this is no
prove that inflation theory is correct.


This is a generic feature of non-empty big-bang models. etc

This does not prove that inflation is correct.


See your document: http://arxiv.org/pdf/1112.1666v2.pdf
Equation (1) is the starting point used in my simulations.
Interestingly you raises the question if there is a flatness
problem in the first place.
For Alan Guth the most impressive piece of evidence is the flatness problem



This is what Alan Guth describes in his book at page 185.
When you study study figure 10.6 my interpretation is, that with inflation
the size is the same but the age is a fraction of a second younger.


I don't follow you here.


Fig 10.6 shows horizontal the time axis in seconds (between 10^-43 and present.
Vertical it shows the Radius of the Observed Universe in meters.
The figure shows the Standard Theory and the Inflationary Theory in two lines.
Both lines start from the left (time 10^-43) untill present.
The ST line starts at Radius 10^-3 and finishes with radius 10^20.
(angle 15 degrees)
The IT line starts with radius 10^-57, almost goes straight up around 10^-35
seconds untill 1 meter and than becomes the same as the ST line.
The text reads: Figure 10.6 Solution to the horizon problem: the size of the
observed universe in the standard and inflationary theories.
If you compare the two lines starting after 10^-30 seconds both are identical.
That means the age of the universe without inflation is only a fraction older.
Ofcourse this is a very unimportant issue.
Important is what are the physical implications of this small period of rapid
expansion and which specific observations are an idication that this is true.

The same problem exists with the horizon problem. First "we" assume a problem.
Next we "predict" a theory which solves this problem. Next we claim that
there is no problem anymore (more or less). An even stronger claim is that
this proves that the theory is correct.
What is so important for the inflation theory is that the details of the theory
are impossible to observe nor predicted observations with and without the theory.
This type of science is completely different compared to the medical
industry where the influence of a medicine is tested with thousand patients
with or without the medicine

What worries me about Figure 10.6 is that it shows the observed radius and not
the true radius which includes all what is changed after the Big Bang.

Nicolaas Vroom
  #22  
Old July 20th 14, 07:55 AM posted to sci.astro.research
Phillip Helbig---undress to reply
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Posts: 629
Default The Observed Universe, Our Universe, Our Big Bang.

In article , Nicolaas Vroom
writes:

The issue is that IMO our primarily interest should be in what you call
"the universe". I would call that "Our universe" created by "Our Big Bang"
completely indepent of any human "behaviour".
The word "our" is only there to allow for more Big Bangs.


I don't think anyone disagrees with this, but we have to keep in mind
that we can infer things directly about the observable universe only.

What I understand is that before inflation the observable universe
was small and equally in size as the (our) universe but after inflation
the (our) universe became much larger as the observable universe.


Right.

If that picture is correct it makes sense to first study the larger
part.


IN PRACTICE, one can't study what is by definition not observable,
except theoretically.

The question arises where is this larger part?
before the CMB radiation or after the CMB radiation?
(relevant to our position)


I guess you mean "before" and "after" spatially, not temporally. The
CMB is at a redshift of about 1000 and the big bang at infinite
redshift. That means that a photon just reaching us now from the big
bang (assuming this were possible in practice; it is not since the
universe became transparent only at a redshift of 1000) has travelled
the maximum distance possible. This is the definition of the observable
universe. Things farther away than that---and hence farther away than
the CMB---are in the non-observable part of the universe.

See your document: http://arxiv.org/pdf/1112.1666v2.pdf
Equation (1) is the starting point used in my simulations.
Interestingly you raises the question if there is a flatness
problem in the first place.


Right. That's the point of the paper. As I mention, though, I am not
the first to claim that the flatness problem is exaggerated and/or
misunderstood. See the references to Lake and various combinations of
Coles, Ellis and Evrard.

For Alan Guth the most impressive piece of evidence is the flatness problem


He's built his career on it.

Bird feathers did not evolve for flying, but for temperature regulation.
So, inflation can still be a useful concept no matter what the original
motivation was. (Actually, Guth was studying the monopole problem and
realized that inflation could solve the flatness problem as well.)

This is what Alan Guth describes in his book at page 185.
When you study study figure 10.6 my interpretation is, that with inflation
the size is the same but the age is a fraction of a second younger.


OK, I get it now. The current size is fixed so, of course, any theory
has to have the current size now. Because of inflation, expansion very
early on was faster so, yes, it is slightly younger. Very slightly.

The same problem exists with the horizon problem. First "we" assume a problem.


There is definitely a problem: Why do two widely separated areas of the
sky have the same CMB temperature even though they have not been in
causal contact?

Next we "predict" a theory which solves this problem.


A theory which solves the problem is more interesting, but inflation was
not constructed to solve the horizon problem.

Next we claim that
there is no problem anymore (more or less).


If inflation solves it.

An even stronger claim is that
this proves that the theory is correct.


In general, one can never prove a theory. One can disprove a theory.
However, observational and other evidence can increase our confidence in
a given theory.
  #23  
Old July 22nd 14, 06:29 PM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default The Observed Universe, Our Universe, Our Big Bang.

On 7/20/14, 1:55 AM, Phillip Helbig---undress to reply wrote:
I guess you mean "before" and "after" spatially, not temporally. The
CMB is at a redshift of about 1000 and the big bang at infinite
redshift. That means that a photon just reaching us now from the big
bang (assuming this were possible in practice; it is not since the
universe became transparent only at a redshift of 1000) has travelled
the maximum distance possible. This is the definition of the observable
universe. Things farther away than that---and hence farther away than
the CMB---are in the non-observable part of the universe.


Observable universe
is still an open question in terms of high energy Cosmic Rays.
At what redshift are they produced?
Some data is available:

Indications of Intermediate-Scale Anisotropy of Cosmic Rays
with Energy Greater Than 57 EeV in the Northern Sky
Measured with the Surface Detector of the Telescope Array Experiment
http://arxiv.org/abs/1404.5890

Although the Telescope Array Experiment observed Cosmic Rays
with Energy Greater Than 57 EeV appear with an anisotropic hotspot,
their rate fall within an isotropic generation of ~ 1/km^2/year

Richard D Saam
 




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