The Multiverse

Someone who hasn't been living under the rock for the past ten years must've heard the term 'Multiverse'. In the beginning, we thought that our Earth is the center of everything and the Sun rotates around the Earth. Then came Galileo, who told us that  our earth is not the center of everything. Instead, It is the Sun which is at the center and our earth and other planets rotate around it collectively forming the solar system. Later, it was found that our solar system is not the only one, and there are other stars too, much bigger than the sun an that there are an infinite number of stars & galaxies adding up to make everything that was there; "The Universe".
In the 1980s, Stephen hawking claimed that physics is entering into a new realm, and soon we'll be able to read the mind of God and understand why everything is the way it is. But the nature had different ideas. Just when the physicists though that they were about to find the theory of everything, something incredible, something astonishing was brought to light during the quest; the idea of more than one universes or the Multiverse. The basic questions which may arise in someone's mind at this point  might be: "What is Multiverse?", "Why do we believe in something which cannot be seen or observed?"

Let's discuss three different theories, from different fields, all of them pinpointing towards the idea that our universe may not be the only one.

1. The Theory of Inflation:

It all started with the quest of explaining The Big Bang. According to the big bang theory, our universe was formed as a result of an intensely violent explosion; The Big bang. But one thing which it doesn't really explains is the bang itself; "what bang?" , "why bang?", and "what caused the bang?". So basically it was like saying that everything just came out of nothing. In the beginning there was nothing and suddenly that 'nothing' exploded and the stars and galaxies came into existence.
In 1979, Alan Guth, currently a professor in the MIT, got interested in explaining the formation of particles at the time of big bang. And after years of research, he found something amazing; the math that could explain the formation of particles at the time of big bang suggested that at the very beginning, gravity would've acted in reverse. Instead of pulling things together, it would've repelled everything around it. Its consequence was the big bang. Described mathematically, this force was so powerful that it could blow a molecule to the size of the milky way galaxy in a billionth of a billionth of a nanosecond. And these equations explained the formation of stars and galaxies just as the big bang theory. The powerful repulsive force of gravity was what which caused the big bang. Guth called this burst as inflation. The reason why inflation theory gained so much popularity was that it could be tested through observations. According to physicists,  If this theory were right, there should be some heat and radiation due to the  inflation, left in the space, in the form of cosmic background radiation. So in 2001, NASA cosmic background radiation explorer was launched which measured the amount of heat and radiation very precisely. And surprisingly, It was exactly in accordance with the values predicted by the inflation theory. Guth had no idea what could be the implications of his theory. He said:

"I had no idea what could be the implications of my work, I was more, looking for a permanent job."

At that time, there were two scientists; Andre Lindae, and Alex Vilinken who believed in the idea that our universe may not be the only one. Alex Vilinken discovered form the equations of inflation theory that; inflation never occurs every where at the same time. Instead, there is always a series of inflations. According to him, there could be a space out there in which  energy is distributed in an irregular manner, when the concentration of energy at a point increases immensely, inflation occurs an a new universe is born,  Which means that there were more inflations before the inflation which made our universe and there were probably many more after that, forming other universes.

the phenomenon of universes being born in the model of inflation theory according to Alex Vilinken

Alex Vilinken  wrote more than a dozen of research papers explaining this Idea. But at that time, the scientists were least interested in a hypothesis which could never be tested.

 

     2. The Dark Energy:

In 1990s, the astronomers discovered the most disturbing, perplexing and bizarre fact of the decade; that the expansion rate of our universe is continuously increasing. This was a disaster for the physicists at that time. To understand how confusing this is, imagine that you throw a baseball in the air, common sense says that as it will move forward, it will gradually slow down because the gravity will pull it back. Or if somehow, it leaves the gravitational field, it will move at the same speed. How bizarre it would be, if the ball itself continues to speed up for ever? 

Thus, the astronomers discovered that there was some kind of force or energy, which was present in the space throughout the Universe which was acting as the driving force, they called it as the dark energy. The 'dark' itself explains why it is named as dark energy. Because we cannot observe it, we have no idea what kind of force it is and why it is there. Only one thing which the scientists discovered by the math, was that it is really in a very small quantity. something like to the trillions of the trillions of  the trillions decimal points. Such a small amount of energy is making the entire universe to accelerate at a grater and greater rate. Plus, if this energy had been a just a little bit more than it is, the stars and planets could not have been formed because of the immense acceleration provided by this energy. And for a little smaller amount, the universe would've collapsed within itself. This perfectly right amount of dark energy allowing every thing to exist and function elegantly and smoothly was quiet amazing. But its occurrence cannot be explained if our universe is considered to be the only universe. This amount of dark energy and its existence perfectly fits if we consider that there are more Universes present other than our universe. And it all goes down to the probability, in some universes, due to a different amount of dark energy, the laws of physics would probably be completely different. And in the others, matter as we know it, probably doesn't even exists.

This made the scientists to reconsider the idea of Multiverse. And after 10 years of darkness for Alex Vilinken, the discovery of Dark energy wasn't less than a bright sunshine.

       3. The string theory:

String theory was a giant leap forward in the process of understanding and explaining the Universe. Some of the quantum physicists claim that, in the future, the theory of everything will be the modified form of string theory. According to this theory, deep inside the sub-atomic world, in the world smaller than the quarks, there are strings which make up everything. Strings vibrate and move in different dimensions in a manner which  determines what sort of particle or matter it would from.

 strings vibrating at different frequencies

Surprisingly, the math of string theory suggests that strings can move in  six more spatial dimensions in addition to our common three spatial dimensions; the height, width and depth. These extra or hidden dimensions are very small and curled up within the strings and are present at every single point in space and act as the DNA of the universe, determining its behavior. Which means that the behavior of the Universe is determined by how these strings move in extra dimensions.

Strings jumbled up , acquiring different shapes at each point in the space

But the problem was that the more the scientists looked deeper into it, the more ways they found for the strings to move  in these extra dimensions. More than 500 research papers were published, each one giving a right solution, and each one explaining different ways for the strings to move in the extra dimensions.  But what kind of theory suggests more than 500 different  correct solutions for a single problem. This made the string theorists somewhat unhappy, somewhat depressed. However, some string theorists found it amazing, they looked the other way around. They looked into it as an enormous amount of probabilities and found that this theory fits extremely well into the ideas of cosmology and physics related to Multiverse. With each probability corresponding to another universe.
String theory without even trying, solved the problem of Multiverse. Explaining how could they be formed by the particles at the tiniest level.

However, some physicists argue that science is about the evidence. And no such experiment has been carried out, or even an observation which has been made that would make them to believe in the idea of Multiverse. But during the last few centuries, mathematics had predicted the presence of things like black holes etc. well before the experimental evidences were provided. There was a time when people didn't believe that the earth is spherical or there are other planets too. Furthermore, three different lines of reasoning point towards the same idea. And just as it takes three legs to support a stool. Three different theories form different fields make this idea very convincing that our universe is not the only universe, and there may be infinite number of universes out there making up 'The Multiverse'. If you consider this mind-blowing, reconsider your thought because there is a next step to it; the parallel universes having parallel realities. What I mean is, in one of the universe out of infinite universes out there, there might be one exactly like ours, having a galaxy like the milky way and a nice planet just like the earth rotating around a sun alike star. Except for small differences like; in one of them, Einstein may still be alive. Or  U.S.A may be a colony of British Empire. In one, you might be rock star. In one, you were never born.