Parallel Universes or "Multiverses" that most people used to see in Sci-fi are one of the serious research topics of many physicists, mathematicians, and cosmologists. According to a group of scientists which includes David Gross, the idea of the multiverses are far from reality and not an elegant one. However, for some scientists like Alan Guth and Andrei Linde who have established themselves in science, this concept is very elemental one and it is the necessity of the mathematical equations' results. There are also String Theoreticians like Brian Greene who has already written books on it.

If Multiverses really exist, they could be very complex for our reality perception than we guess. If so, unlike we think it is unique and sole, our 13,7 billion years old universe could be a little part of a huge and procreant structure!

^{Img Source: Express.co.uk}

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Introduction

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The foresight of the multiverses had started on the probability calculations of having a twin brother somewhere in the universe if it is infinite. Some quantum mechanics physicists proposed that if one of the values of all quantum states for a quantum system happens in this universe, then other probabilities would have occurred in other universes as a physical reality. Since this approach is an interpretation issue, science environment didn't take it that much seriously at first. But the subject which is telling that the existence of other universes beyond ours came to the fore upon the proposal of inflation and string theories which the astronomers and the physicists mooted in the 1980s. The topic had earned its reputation back under the name of "multiverses" or "multiverses model". And this time, not as a speculation and an interpretation of the physics equations, but as the foresight of the equations itself. Up to that time, the Standard Big Bang Model was the most successful universe model.

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^{Hugh Everett was the quantum scientists who proposed "Many worlds interpretations". Img. Source: azquotes.com}

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Standard Big Bang Model

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The existence and the abundance of the light elements such as Hydrogen and Helium are well explained very successfully in Standard Big Bang Theory. Yet it is inconsistent with some very fundamental realities. For instance, according to this model, the particle amount cannot reach up to 10.000 (10⁴) particles. It is well known that there are 10⁹⁰ sub-atomic particles in the universe. The universe doesn't have any monopole magnetic material, however, the Standard Big Bang Model proposes that those kinds of particles had occurred in the beginning. Another important point is the uniformity issue. The uniformity is telling that the material density in the universe does not change too much. It only differs 1/10.000 along the distance of 10 billion light years. Another experimental observation indicates that the temperature difference is only 1/100.000 in the universe wherever we point our measurement devices at. It is also another inconsistency with the Standard Big Bang Model. Moreover, this theory cannot explain one another question which the humanity is interested in: "What was there before the big bang? How everything came out of nothing? How all went well and as its consequence the humanity came up? All those questions were on the side of spiritualism but now the things are changed. Nowadays Cosmology is literally concerning for these subjects exactly.

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Inflation Of The Universe

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Alan Guth developed the "Inflation Theory" on 1980s. Because the Big Bang theory couldn't explain what is banged and how it happened. It only related to this "bang". As Guth's theory says, the universe has had an inflation duration in the beginning which continued for 10^-35 seconds. This inflation progress was the fastest thing which anything had ever happened until now. During this incredibly tiny period of time, the universe expanded exponentially which is 10²⁵ times more than its volume. It crescively got bigger from a sub-atomic size to a size that is larger than our observable universe. Of course, this rapid inflation resulted in the rapid cooling of the universe as well. Guth emphasizes that some fluctuations happened in the universe which is like the phase transitions of a liquid while cooling below the freezing point. Guth also explained the phenomenon of inflation with the existence of an exotic sub-atomic particle although the universe has the gravity force against it.

The inflation theory is one of the recognised and popular model at the moment because it confirms uniformity data of the universe. However, according to Andrei Linde, who is a Russian scientist from Stanford University, there is no need to accept the explanations of the universe's expansion which are only based on thermodynamic principles.

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As Andrei Linde moots, new universes could be born in each of the space-time regions where the energy density is high.

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^{Andrei Linde applied the scalar fields which are used for the calculations of the sub-atomic particle interactions to the beginning of the universe}

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Multiple Universes And The Inflation Theory

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Linde took into account each energy value in the beginning of the universe, which the scalar field probably could have. and he calculated the states which ones could cause the inflation. The scalar field was not smooth and flat like a lake but wavy and fluctuant like an ocean. In a way of more scientific explanation, in the scalar field what the vacuum is made of, has continuous fluctuations of energy and quantum waves. Those fluctuations happen in a very small period of time and impossible to observe. They sometimes cause macroscopic-sized inflations and thus they initiate newly born universes. As the universe expands, the fluctuations are also propagated. Therefore energy density increase where the waves superpose each other. And also the energy density decreases where those fluctuation waves interfere each other destructively. Thus some parts of the universe became cooler whereas the other parts were hotter.

The fields which have high energy density ceases expanding and after that it explodes and inflates. The fields which have low energy density goes on expanding. The explosion and respective inflation of high-energy fields refer to the creation of the new universes. And so the islands of the universe are being created in the Mega-Universe ocean. Inflation theory tells us the big bang didn't happen only one time. In the history of Mega Universe, this happened many times and will be going on forever.

Let's turn back to the question of "what was there before Big Bang? and how everything is created from nothing?". As Linde's theory says, there was a scalar field before the Big Bang and everything, our universe, and other universes existed because of this field's quantum fluctuations. And as a consequence, one could ask that "what was there before the scalar fields?" Another scientist, Alexander Vilenkin has some answers to this question. He theorizes that there were only Mathematical equations at first. He modeled the approaches of quantum tunneling and four-dimensional sphere for his solutions in order to explain for the coming out of nothing.

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Conclusion

Before the Inflation and String theories, multiverses are never been interested in the academic literature. It has always been a subject of Sci-fi industry. But the 1980s were a milestone for this theory. Those theories opened a door to the scientists for a comprehensive explanation of our existence by its compatibility with the Quantum Mechanics. But the discussions on this topic never seem to end in the near future. Before anything else, acceptance of the theories which will never be proven by any experiments should be well defined.

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References

1. Big Bang Discovery Opens Doors to the "Multiverse"
2. Calabi-Yau Manifold
3. The most detailed model of the universe: Scientists map our 'lumpy' cosmos using Einstein's theory of relativity
4. Andre Linde's Inflationary Cosmology
5. LHC proton-lead collisions may have created new form of matter
6. First evidence of the multiverse? Scientists think Cold Spot in space could be colliding universes
7. Parallel Universes source: "Science and Technology Magazine of scientific and technological research council of turkey, issue 43, vol.513, p.38-46, 2010"

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