Big Bang, Inflation Theory & Cosmic Microwave Background radiation

 Question 1 Critical Evaluation Inflation Theory Question 2 Cosmological Horizon Question 3 Is the universe homogeneous and isotropic ? Question 4 Can the Universe be closed ? Question 5 Observable Universe and or Visible Universe Question 6 What can we learn from the CMB radiation?

Introduction

The purpose of this document is not so much to answer questions but to express my personel opinion about certain issue's.

Answer Question 1 - Inflation Theory

The Big Bang Theory assumes that the Universe started from a singularity with a Big Bang. A singularity is a point with infinite mass, temperature and energy. After the Big Bang the universe expanded in size. Roughly speaking the expansion is almost linear. The current opinion is that at present this expansion is accelerating.
The Inflation theory assumes almost the same as the Big Bang theory except that immediate after the Big Bang during a small period of time the size of the universe increased tremendously. After this period the expansion is the same as in the standard Big Bang theory.

The evolution of the universe is a physical process.
In the Book "the Big Bang" joseph Silk at page 72 discusses a number of Era.
He considers:

Singularity, Planck time, Inflation, Hadronic Era, Leptonic Era, Radiation Era, Matter Era and Decoupling Era 300000 years after the Big Bang.
The biggest problem with the inflation theory is that when you introduce a two small period of discontinuous behaviour you have to explain in detail which chemical reactions caused this process to start and which reactions or conditions caused this process to stop throughout the universe all at the same time. This is a difficult process to explain.
Certain physicists try to explain this by the concept called symmetry breaking. The problem is when you try to explain something with something that is not clear the overall result is more confusion.

The same problem arises when you try to explain something by means of a field. In this case this is called an inflation field. When you study inflation there are many inflation fields all with different shapes. The problem is IMO that in most cases the field is modelled such that its fits what your theory predicts but that there are no experimental individual observations or test to demonstrate that the field has the actual supposed shape.
Also in this case you replace something that is unknown by something else that is unknown.

For a critical evaluation what is written in Wikipedia about inflation select this link: 'Inflation (cosmology) in Wikipedia'

For a critical evaluation of the book "The Inflationary Universe" by Alan H Guth in 1997, select this link: Book Review

Answer question 2 - Cosmological Horizon

The Cosmological Horizon reflects the distance we can observe in space. The concept is closely related to the Observable Universe . The Cosmological Horizon resembles the horizon we can see from a point at the surface of the earth. The Cosmological Horizon also reflects the distance we can communicate between two points A and B.

The central problem with the cosmological horizon is that it has to do with human observations. The problem is that human observations can not be used to explain the physical process happening during the evolution of the universe. Except how humans change the habitat on Earth.

It is worse to use the Cosmological Horizon as an argument in favour to support the idea that immediate after the Big Bang there was a period of rapid inflation or space expansion. The reason is that there is no physical link between an Horizon and the chemical reactions that took place during that process.

It is a fact that of the present state of the universe we can only observe a tiny bit. Most of the present day universe can not be observed. This becomes more stringent when we call the entire Universe (assuming that entire Universe means all that was influenced, created, formed after the Big Bang) at present homogenous and isotropic. The problem is we cannot observe the outer edge of this universe so how do we know it is.
The point is that all of the present day galaxies we can observe but not in there present state but more in their infancy. The higher the measured z values (redshift) the younger.

See also The Inflationary Universe - by Alan H Guth page 183

Answer question 3: Is the entire universe at present homogeneous and isotropic.

A Slightly different question is: Was the entire universe always homogeneous and isotropic?
It is very important to make a different between we humans observe and the entire universe at present. With entire Universe we mean all of space that is effected by the Big Bang.
As explained in Question 2 we can only observe a tiny bit of the Universe at present. The earliest we can see is the Cosmic Back Ground radiation which is rather uniform. The CMB radiation originated 300000 years after the Big Bang when the universe was very small. The CMB radiation observed came from a sphere of roughly 900000 light-years. To what extend this sphere is a good representation of the entire universe as of that moment is speculation.

In order to study the size of the entire universe, using Friedmann's equation and based on the mainstream accepted cosmological parameters, please study this: Friedmann Lambda=0.01155 What this document shows:

1. First the path of a light ray (of events) emitted starting very close to the Big Bang. (blue line)
2. The size of the entire universe as a function of the age of the universe. (black line)
When you compare the blue line with the black line you can see that of the entire universe we can only observe a tiny bit at present and that the size of the entire Universe is approximate 35 billion light-years
IMO the best answer is that our local universe (radius 1 billion light-years) is more or less homogeneous but that we can not answer this question for the entire universe.

The problem is that when space expansion is not continuous there is a higher chance that the entire universe as a whole becomes more inhomogeneous.

Answer question 4 - Can the universe be closed.

This question has to do with the evolution of the size of the Entire Universe. In theory there are three physical options.
• The size of the universe will exponetial expand. That means the density is lower than the critical density.
• The size of the universe will increase with a constant rate. That means the density is equal to the critical density.
• The size of the universe will reach a maximum and then decrease. That means that the density is larger than the critical density. This is called a closed universe.
The most probable option is number 1. The least probable option is number 3.
Option number 2 requires that this situation already existed within the Big Bang.
In principle it is possible that after space expandsion certain parts of space can start to contract. The problem is that this never will be in the entire universe in harmony, all at the same time and than all to the same center point.
Mathematical this is may be possible but the evolution of the universe is not mathematics but physics.

Answer question 5 - Observable Universe

The Observable Universe is defined as the present space occupied by the galaxies, including the CMB radiation based on human observations. This is a typical human based concept.
The observable universe defines a universe which we cannot observe directly and is based on the Friedmann equation. What exist is the entire universe which is defined all that is created after the Big Bang.
The entire universe at present is larger than the observable universe. The issue is how much larger If the difference is caused by inflation than this should clearly mentioned.
IMO we should not use the concept of observable universe as a concept to understand the evolution of the universe in time.
That does not mean that we do not use observations in order to understand the evolution. The opposite is true.

The important part of that document and the link mentioned is that the distance of the path of a light ray, which originated from as far ago as the CMB radiation or later (the blue line), is not so large. This distance is much smaller as the size of the entire universe.
What we should see along the blue line is that the furtest galaxies should have a young appearance while the closest galaxies should look mature.

Answer question 6 - What can we learn from the CMB radiation.

The Cosmic Micro Wave background radiation is electromagnetic radiation that was created 380000 years after the Big Bang.
The fact that the CMB radiation is detected is considered as proof that there was a Big Bang i.e. that the Universe started as a "singularity", a point of "infinity" density and temperature.

Literature

Created: 14 October 2014