Comments about "Universe" in Wikipedia

Introduction

This document contains comments about the document Universe in Wikipedia
To order to read the document select:http://en.wikipedia.org/wiki/Universe In the last paragraph I explain my own opinion.

Contents

Introduction

The Universe is all of spacetime and everything that exists therein, including all planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy.
This is a rather vaque definition. This definition would be much more practical when you define concepts like Entire Universe versus Local Universe.
Next sentence:
The estimated diameter of the observable universe is about 93 billion light years or 28 billion parsecs. Scientific observation of the Universe has led to inferences of its earlier stages.
Here they introduce the concept of observable universe which has a radius of 46 billion light-years without an explanation what the difference is.
These observations suggest that the Universe has been governed by the same physical laws and constants throughout most of its extent and history.
A difficult to understand sentence. The real issue is that generally speaking througout the whole evolution of the entire universe at each era the same chemical processes took place.
The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe, which is calculated to have begun 13.798 0.037 billion years ago.
The issue is what do they mean: (Entire) Universe or Observable Universe.
Observations of supernovae have shown that the Universe is expanding at an accelerating rate
The issue is what do they mean: (Entire) Universe or Observable Universe.
What is really important is what we know or assume about the Entire Universe since the Big Bang.

1. Historical observation

Throughout recorded history, several cosmologies and cosmogonies have been proposed to account for observations of the Universe.
IMO what we are discussing here in this sentence is the Observable Universe

2. History

According to the prevailing scientific model of the Universe, known as the Big Bang, the Universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable universe was concentrated.
Again here they play with two concepts universe and observable universe which makes the sentence difficult to understand.
My first impression is that they mean "Entire Universe" because the issue is all matter.
The universe is composed of ordinary matter (4.9%) including atoms, stars, and galaxies, dark matter (26.8%) which is a hypothetical particle that has not yet been detected, and dark energy (68.3%),
With universe do they mean entire universe ?
All these parameters are calculated based on observations. If these observations are based on local observations than the parameters represent the local universe.

4. Size, age, contents, structure, and laws

The size of the Universe is unknown; it may be infinite
I expect they mean Entire Universe i.e. all of space influenced by the Big Bang
The CMB radiation shows the outer edge of a sphere of what we can observe.
The first question is what is the size of this sphere at the moment 380000 years after the Big Bang.
The second question is how much larger was the entire universe as of that moment.
To assume that it was infinite as of that moment raises the question: What means infinite. IMO only total space is infinite.
The region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years, based on where the expansion of space has taken the most distant objects observed.
The region visible from Earth at present is small.
The region from Earth were all space has taken after the Big Bang is 46 billion light years. The most distant are the present regions of the CMB radiation.
The observable matter is spread homogeneously (uniformly) throughout the Universe, when averaged over distances longer than 300 million light-years.
Again here you should use the concept of Observable Universe instead of Universe.
See also: Answer question 3: Is the entire universe at present homogeneous and isotropic.

7 Shape of the Universe

The shape or geometry of the Universe includes both local geometry in the observable Universe and global geometry, which we may or may not be able to measure.
If you want to discuss the shape of the (Entire) Universe you first must have a clear difinition of what you mean by (Entire) Universe secondly what you mean with shape and how you want to establish that different shapes are possible which is which.
IMO the shape is impossible to measure.
A complete different issue is that you cannot describe the concepts of shape and geometry in one sentence because the first is physical and the second mathematical.

Reflection 1 - General

When you read the whole Wikipedia document "Universe" there is a continuous struggle between the concepts Universe, Entire Universe and Observable Universe. Which is which is not clear.
IMO the whole concept of "Observable Universe" should be dropped because it is a concept with a human touch.

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Created: 15 November 2014

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