1. THE BEGINNING – A COSMOLOGICAL MODEL

                            Singularity- that extremely hot and unimaginably dense primordial patch of spacetime- exactly where we reach after traveling back in time at least 13.7 billion years when we are asked about the beginning of the universe. That very tiny region from which the universe is said to have emerged. Our present knowledge about the universe starts from it.

The most successful model on the origin of the universe is the big bang theory which explains that universe started from the expansion of a tiny, hot and extremely dense fireball of hot particles and radiations. Of course, the primordial patch contained all the energy of the universe and precisely it was the expansion along with energy-matter conversion which created all the matter and radiations including all the planets, stars, galaxies, galactic clusters contained within the unimaginably vast universe. The rate of the expansion was unbelievable in the sense that in the first 10^-35th second, the universe had grown to the size of 10^(10^12) cm (trillionth power of ten) in diameter. The energy which propelled the expansion was very high that the actual size of the universe may be many times compared to what we observe today since the universe had been expanding for at least 13.7 billion years which is supposed to be the age of the universe.

Big bang model is successful in that it precisely predicted the relative amounts of hydrogen and helium- two of the most abundant elements in the universe. Also the microwave energy- the cosmic microwave background radiation was detected which is a relic of the expansion. The most important proof which confirmed the big bang model was the discovery that universe is expanding by Edwin Hubble in 1929. But the drawback of big bang model was that it did not explain the singularity, how it came into being and what caused it to bang. However the situation was resolved to a great extent by the inflation theory which explains the events leading to the bang and what caused it to bang.

Inflation theory explains that the singularity or the primordial patch contained within it vacuum fields which when fluctuated created a bubble of false vacuum containing enormous anti gravitational energy and it later decayed producing the expanding fireball. But inflation theory also starts from the singularity and gives us no details of what was there before it and what created it.

Two other models on the origin of the universe are- the instanton theory by Stephen Hawking and Neil Turok, multiverse theory by Andrei Linde. Of these instanton theory is a pure mathematical model and it explains that initially the universe sprouted from a region where space and time blended into one called the pea instanton such that all the physical laws are satisfied within it. But it does not explain how the universe originated. Linde's multiverse theory explains that the universe that we see today is nothing but a part of a multi-branching universe which was inflated from a pre-existing region and that region in turn inflated out of another pre-existing region. Thus he travels progressively backwards in time so that we cannot explain actually what happened in the beginning.

Both these theories and some other cosmological models provide an uncertainty about the origin of the universe. They indicate that the universe was created from nothing, but actually it is not.

What exactly do we mean when we refer to the word origin? - Creation of the primordial patch of spacetime? Nucleation of the bubble of false vacuum? Decay of the bubble releasing the enormous amount of energy contained in it creating the expanding fireball of particles and radiations? or Was it the very instant of the bang? We assume it to be the instant of the bang. Both instanton theory and the multiverse theory do not explain the creation of the singularity (the primordial patch of spacetime). Inflation theory successfully explains the bang and the events leading to it. So it is a theory of the bang, a formalism used to explain the big bang.

It also starts from the singularity and explains in detail the events leading to the bang. But it gives us no idea about the creation of the singularity or what was there before it. But it certainly provides us hints to what happened before the creation of the singularity and what might have led to the creation of it. Let's go to the details of inflation theory proposed by Alan Guth- Inflation theory explains that the primordial patch of spacetime contain vacuum dominated by energetic vacuum fields. As these vacuum fields fluctuated, their potential energy increased and decreased. During these fluctuations of the energetic scalar fields, they got temporarily stuck at a high value. These stuck scalar fields caused a bubble of false vacuum to nucleate from it, the peculiarity of the bubble being that it contained a large amount of anti gravitational energy which caused the bubble to expand.

Guth explains that as the bubble expanded, the energy density within the bubble would have remained constant and so the energy content increases as the bubble expands. This gives the impression that energy is being created out of nothing and so he calls it positive energy and in turn calls inflation “the ultimate free lunch”. To explain this he suggests that an equal amount of negative gravitational energy of the ordinary attractive kind was created simultaneously during the expansion and the net effect is zero. Basically this was an assumption to satisfy the law of conservation of energy and he admits that the total energy of the system is conserved.

But how can we explain the creation of such a huge amount of anti gravitational energy and the positive energy that builds up from within the primordial patch of spacetime which contain nothing but vacuum fields confined within a very small region (patch)?

Well, the situation can be explained with some other concepts as follows- Before the origin of universe by big bang or before the beginning of time (which was the instant of the bang) or in other words the pre-big bang universe contained only vacuum consisting of a finite amount of energy (of very large magnitude) in the form of vacuum fields which is the total energy of the observable and the unobservable universes together. All the matter and radiations now seen in the universe was created from this energy (a part of it) and the rest probably remains as the unobservable or in the form of dark energy.

Now the case of Guth's positive anti gravitational energy and the creation of the primordial patch of spacetime- According to Einstein's theory of relativity, mass and energy are equivalent and if matter is able to exert gravitational pull, then so must energy. The pre-big bang universe which contained energy in the form of vacuum fields exerted gravitational pull on the surrounding region which eventually increased the energy density of that region. Consequently all the surrounding regions containing the vacuum fields were pulled into that region so that they collapsed into it causing the region to become progressively smaller, denser and denser. Thus the primordial patch (the singularity) was created which contained all the vacuum field energy within it. These vacuum fields then fluctuated to produce the bubble of false vacuum which was actually not created from nothing, but from the region containing vacuum fields and vacuum field energy. Eventually the false vacuum decayed and the energy of the vacuum fields contained within it was suddenly released, creating the expanding fireball of radiations and hot particles.


This concept suggests that the initial singularity was produced by the action of gravity on vacuum fields. Thus the universe was not created from nothing - but from a finite amount of energy present even before the beginning. The extremely high energy density of the initial singularity would require it to have undergone a period of contraction of the vacuum fields containing all the energy of the universe driven by gravity or some other mechanism to satisfy the law of conservation of energy.