BIG BANG  A-Z  For Layman

                                           - By Chirag Joshi.

Abstract

There are two major theories about the creation of the universe. The theories are the Big Bang theory and the Steady State theory. This paper mostly focuses on Big Bang theory and how universe expands after that. This paper also give ideas about the alternative theory of the Big Bang called the Steady State theory, and also what the Steady State theory proposes about the creation of the universe.

How are the universe at the time of Big Bang and the universe of now similar? How they are different?

There are lot of thoughts and theories out there about the beginning of the universe, but the most widely accepted one is the Big Bang theory. Although it contains lot of contradictions, the Big Bang theory is extensively accepted. But how did scientists develop the Big Bang theory, who were the people who suggested this theory, and how does this theory relate to the universe as it is?
 

Georges Lemaître, a Catholic priest from Belgium, first proposed the idea of a universe born at a single instant in the past and expanding outwards from that moment (Singh). According to Wikipedia encyclopedia, Lemaître worked out a solution to Einstein's equation but he is better known for having introduced the idea of the "primeval atom." He stated that galaxies are fragments that have been ejected by the explosion of this atom, resulting in the expansion of the universe. Lemaître took cosmic rays to be the remnants of the event, although it is now known that they originate within the local galaxy. He estimated the age of the universe to be between 10 and 20 billion years ago, which agrees with modern opinion (Wikipedia).
 

At this time, Einstein, while approving of the mathematics of Lemaître's theory, refused to accept the idea of an expanding universe. He believed the universe was immutable, but would later recognize that this prediction was the greatest error of his life (Wikipedia). After the Belgian detailed his theory, Einstein stood up, applauded, and said, "This is the most beautiful and satisfactory explanation of creation to which I have ever listened" (Wikipedia).
 

In 1933, when he resumed his theory of the expanding universe and published a more detailed version in the Annals of the Scientific Society of Brussels, Lemaître achieved his greatest glory. The American newspapers called him a famous Belgian scientist and described him as the leader of the new cosmological physics (Wikipedia).
 

Edwin Hubble was the first American astronomer to find physical evidence of the universe's expansion, in 1924 (Dolan). At about the same time, other astronomers were trying to find theoretical proof of the same phenomenon. According to Dolan, Hubble discovered that galaxies all around the earth were moving away from the earth. This was discovered because of an analysis of the light coming from the different galaxies. He theorized that lights coming from all the galaxies were red shifted. Red shift is when the light an object emits is displaced toward the red end of the spectrum. Because it is going towards the red, it known as red shifted. Often, the red shift of an object can be measured by examining atomic absorption or emission lines in its spectrum. The motion of a source away from an observer can cause red shifts. For distant objects, red shifts can be caused by the expansion of the Universe.
 

Hubble also found that the further away the galaxy, the faster it is going away from the Earth (Dolan). In 1927, Hubble used Einstein's equations to calculate that the universe was expanding. Then he went on to speculate about how that expansion had begun. His theory was that all the matter in the universe had originally been squashed into one incredibly dense primeval atom. This atom, which he also called the "cosmic egg," had at first slowly disintegrated (Dolan). But then it had become unstable and exploded. As a result, all the matter it contained was still flying apart. In later years, this explosion becomes known as the Big Bang.
 

Scientist today theorizes that Big Bang occurred about 15 billion years ago. Now the question is, "how did they deduce that Big Bang occurred about 15 billon years ago?" Years ago there was an unsuccessful attempt made to find the age of the universe through trigonometry. Scientists tried to calculate the diameter of the Earth's orbit around the sun and use it to triangulate the distance to a galaxy far away (see below). However the orbit of the Earth is not fixed. It changes as the sun moves around the galaxy (LaRocco, Rothstein). So the distance from the Earth to any particular galaxy also changes

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