The question that has fascinated man since he developed cognitive sense and set him thinking on, is what is the origin of this universe and how it evolved to its present form? This question of how the universe came into being and how it evolved to its present form attracted the attention of not only Greek philosophers but poets, scientists and common man equally from time to time. The problem of the origin of the universe in earlier times as Stephen Hawking says was a bit like the old question: which came first, the chicken or the egg? In other words, what agency created the universe, and what created that agency? Or perhaps the universe, or the agency that created it, existed forever and did not need to be created. Till the 1950s, most philosophers and scientists reposed their faith in the static universe model. The static universe model held the belief that the universe is unchanging with time and argued that the universe was both infinite in size and eternal in duration or in simpler words it argued that the universe had existed and will exist forever. This model was accepted not because it was supported by observational evidence but because these people believed that something that is eternal was more perfect than something that had to be created. Dennis Sciama, a longtime friend of Fried Hoyle in his defense of the steady-state model once pointed out so beautifully and eloquently that he defended this theory not because he deemed it valid, but because he wished that it were valid.
Immanuel Kant in his monumental book “Critique of Pure Reason” considered one of the most influential works in the history of philosophy even argued that there were equally valid arguments for believing that the universe had a beginning and for believing that it did not. The Greek philosopher Aristotle too believed that the universe did not have the beginning in time and that matter was eternal. However, the problem with these conclusions lies in the fact that they are based on pure reason and not on any kind of observation. Furthermore, a difficulty in a static universe as Hawking argues in his book ” Brief History of Time” is that according to Newton’s law of gravity a star ought to attract every other star, would not they all fall together in s Static case then?
Shedding his further deeper insights on the issue, Stephen Hawking in his book “Blackholes and baby universes” writes that in the 19th century, evidence began to accumulate that the earth and the rest of the universe were in fact changing with time. The evidence that the universe is not static was provided by the 2nd law of thermodynamics formulated by German physicist Ludwig Boltzmann which states that the total amount of disorder in the universe (disorder is measured by a quantity called entropy) always increases with time. This suggests that the universe has been going only for a finite time. Otherwise, in the case of an infinite history, it would by now have degenerated into a state of complete disorder, in which everything would be at the same temperature. so all these astronomical observations were in total contrast with what the static universe model argued for. So the model of the static universe was dispensed away within the 1950s owing to its failure to account for major astronomical observations.
Scientists since the 1950s explain the creation of the universe through a phenomenon called the Big Bang. Big Bang refers to the singularity at which the density and curvature of the universe were infinite and the universe was extremely hot. Precisely it is this singularity where the laws of physics break down). This theory is widely accepted because it is not only supported by reason but by astronomical observations as well. In 1985 a scientist remarked in a scientific meeting ” It is as much true that universe started with a big bang in some finite past, as it is that the earth goes around the sun’.According to this theory, if we take the notion of the present galaxies and run it back in time, it would seem that they should all have been on top of each other at some moment between ten and twenty thousand million years ago. So this whole matter would shrink into a minutely very very small fireball (the dimensions of which we can not define) called a primary nebula. Then through an expansion in this primary nebula some fifteen billion years ago it split up into various fragments which formed the matter for present-day galaxies.
The theory of the Big Bang was first proposed by George Lemaitre in 1927. The model is based on two simple assumptions, one is Albert Einstein’s theory of General Relativity correctly describes the gravitational interaction of all matter and 2nd is the cosmological principle. The greatest evidence in support of this theory apart from Hubble’s discovery in the late 1920s is the discovery of microwave background radiation in 1964 by Arno Penzias and Robert Wilson for which they shared half of the Nobel Prize in 1979. These radiations had the characteristic spectrum of radiated emitted by a hot ball. These radiations are believed to be emitted by the distant parts of the early hot universe and would be reaching us by now only in the form of microwave radiations because of redshift as a result of the expansion of the universe. Acclaimed Nobel Prize-winning American theoretical physicist Krip Throne while commenting on the theory of the Big Bang writes in his book ‘The Science Of Interstellar’ that “we do not know what triggered Big Bang nor of if anything existed before it, but all we know is that there emerged a vast sea of ultra hot gas, expanding fast in all the directions like a fireball ignited by a nuclear bomb blast or the explosion in the gas pipeline. Except that, it was not destructive and that it created everything in the universe.”
Despite its enormous success and wider acceptance in the scientific community big bang theory also has many shortcomings. There remains an aspect of the observable universe that is yet adequately explained by the big bang models At the fundamental level it fails to explain Baryon asymmetry and on the other hand it fails to account for flatness and the Horizon Problem.
To account for some of the problems of standard big bang cosmology Alan Guth in the 1980s proposed the inflationary model. The inflationary model does not replace the Big Bang model, rather it is considered an “auxiliary addition” which occurred at the earliest stages of the universe without disturbing any of its successes. As the astronomical evidence continues to pile up and some exciting physics is likely to come up, for now, we stick with Big Bang cosmology as a comprehensive model for a broad range of observed phenomena.
The writer is a student of Physics, and can be reached at na************@***il.com
Some reflections on cosmological models
