The Large Scale Structure of the Universe - 1

Introduction
The word Cosmology is a word that includes everything. Hence we say that if we are studying Cosmology we are studying everything. No branch of science can claim to have a bigger area of interest than - The study of everything. Even the so called Aadhyaatma has profound implications to the field of Cosmology from the background. This field started from the instance the human race started to reason by looking up in the sky wondering “why it is the way it is?”, and then started to make inference based on their observations. This was it, the beginning of one of the most fascinating and real science of the place in which we originated, survived and evolved till today.
Cosmology has extended its limits of study from the nearby planets, stars to the distant reaches of the universe – The Extragalactic world. It is the study of the large scale structure of the universe extending to distances of billions of light years – a study of overall physical and dynamical behavior of billions of galaxies spread over vast distances and of evolution of this enormous system over billions of years. It may look like an ambitious task at first. One of the questions that might appear is;
Is our knowledge of the laws of nature sufficiently advanced and mature to interpret the information?

Well, to answer this Albert Einstein might help us with one of his famous quotes – “The most incomprehensible thing about the universe is that it is comprehensible”.
Whether we are far from perfect or near to the so called perfection we don’t know! But what we do know is that with the techniques available with us; we still manage to pull out some meaning to the things, events we observe in this universe.
Let us consider this universe as a Physical system subject to the laws of physics, and follow the Procedure of science.

Let us begin the incredible subject!
Wait! Wait! Wait! What am I doing! Let me first introduce some of our heroes and vampires in this system without whom, the film (study) may be a flop.
Length: Normally while measuring distances one uses meter as a unit. Well, that is okay if it is for small distances. But if we are referring to the distance to stars then we measure such distances using light years, while astronomers use the unit for measuring distances as parsecs.
[A parsec (pc) is a measure of distance on the cosmic scale; it is the distance that corresponds to one angular second of the parallax. Since parallax is due to the Earth’s motion around the Sun, the parallax angle 2a is the diameter 2R of the Earth’s orbit divided by the distance d to the star or galaxy.
Thus a=R/d radians which gives 1pc=3.26 light years.]
Time: Well is this a hero or a villain. What ever it is, but its basic unit is second, but we cannot count on seconds in cosmology. The typical unit here is the giga year (1Gyr=10^9 years=3x10^16 seconds).
Mass: The physicist may use the kilogram, but masses of astronomical objects are best expressed in the mass unit of the Sun’s mass M = 2x 10^33 grams.