Cosmology

It is the study of large scale structural behaviour of the Universe taken as a Single whole. Here the Whole Universe is considered to be a Single Entity. Every part of the Universe is mathematically and physically identical to every Other part in its behaviour.All parts of the Universe are in some sense in unison with all other parts.This is the view taken in Cosmological Models.We have to modify this view when considering the inflationary model. What can be rationally (scientifically) known about our Universe? To this question,as old as human history,the “scientific community “ is overwhelmingly unanimous in its answer:presently,the favoured explanatory cosmological model capable of accounting for observational data within our reach and coherent with currently preferred—and as yet not experimentally falsified—physical theories,is the (Standard)BIG BANG model. When considering the large-scale structure of the Universe the basic constituents can be taken to be galaxies,which are congregations of about Ten To the Power of eleven Stars bound together by their mutual gravitational attraction.Galaxies tends to occur in groups called clusters,each cluster containing anything from a few to a few thousand galaxies.There is some evidence for the existence of clusters of clusters (Superclusters),but not much evidence existence of higher hierarchies. Superclusters and Voids(empty regions) have received much attention nowadays. Observations indicate that on the average galaxies are spread uniformly throughout the Universe at any given time.This means that if we consider a portion of the Universe which is large compared to the distance between typical nearest galaxies (of the order of a million light years),then the number of galaxies in that portion is roughly the same as the number in another portion with the same volume at any given time.The distribution of galaxies appears to be isotropic about the observer. We always assume that the distribution of galaxies is both Isotropic and homogenous throughout the Universe as a Working Hypothesis.