When you talk to people most of the time about life and existence, they always want to bring the question about the meaning of life. Most of you think that there should be a meaning, right? We have faced the question over and over again in the childhood life. Maybe our teacher asked us to write an essay or paragraph on it. I remember in my high school final exam, I had to write about the purpose of life. Well, I believe this question as well play a part in building the civilization where we stand today as well as a lot of destruction. But let us dig a bit deeper, shall we? You have seen in any football matches or any sport we toss a coin. A coin has two sides, head, and tail. So, why in this case we just ask what is the purpose of life? Why don't we go to the possibility of what if there is no purpose in life?

What if we just go back to the nothingness we came from? Sounds unimaginable, right? Well, it's not we came out of nothing or maybe a single point as well call it the point of singularity? So, everything whatever exist far and beyond came from a single point. Then what happened? The answer is the boom happened and we call it the big bang. Not your favourite tv serial The big bang theory. Well, it has to do something with the serial though as they talk about a bit of astrophysics and fun. But believe me, it was not that funny boom. I heard in my younger age that every mother has to bear the pain of giving birth so that the newborn can come to earth. We say what a beauty or what a miracle. I agree that it is a miracle. But the mother has to go through the pain beyond imaginable. So, today I am going to talk about that pain, the creation of the universe and what is in it.

image credit :Nasa

A little bit overview

So, maybe you are familiar with the ancient theory of the static universe. This theory was so powerful that even though Einstein found that the universe is not stationary, he added a constant in his theory to make it stationary in his theory. So, what does this theory says? It says the universe is spatially infinite and there is neither contraction or expansion in it. It was first proposed by a mathematician and astronomer Thomas Digges. This kind of universe doesn't allow a curvation of space and time, so in the simple words, we can say it is just a flat universe. But since always progressed as we say that a theory is never 100 percent correct, it is just a way to make things work until a major problem arrives and we need to modify it or change it. Vesto Slipher, an American astronomer was stunned by his discovery of redshift of a spiral galaxy which says it's going far and far away from the earth. It is highly contrary to the theory of the static universe. After a decade another Russian cosmologist found the same case while he was driving Freedman equation from general relativity theory. Then Edwin Hubble put the final arrow in the heart of the theory of the static universe by showing that the universe is indeed expanding.

image credit : wiki Copyright: CC BY-SA 3.0 Johnstone

People say we can't go back to the time. But physicists are very odd in nature. They always do weird assumption. One of the examples is famous. Where we say let's imagine the cow is a sphere. Although those assumptions are really odd it always leads us to a good conclusion in the end. So, if we think the universe is expanding, to see what happened in past we have to go back and see. So if we go back we will find that the universe should be given birth from a single point or in physics we say its point of singularity. All the laws of physics break down there. So, if you ask me the question what was before singularity my answer would be I don't know or nothing as it was the starting point of time. So, this theory of singularity was given by a Belgian Astronomer priest who said from this singularity happened the big bang

image credit : Hubble ESA Copyright: CC BY 2.0

The first three minutes

What happened after the big bang? To answer that in short let us talk about the first three minutes after the big bang. It was a set of formation towards heavier elements from the lighter. First few seconds matters were formed through pair production after that deuterium was formed by the proton and neutron fusion and then came helium from deuterium, proton and neutron fusion.

Elements like Hydrogen or helium were produced in the first few mins after the big bang. There is the theory of nucleosynthesis about what happened in the first few minutes which is supported by evidence from the very old stars. It was found that 75 percent of it is hydrogen and 25 percent is helium and almost no heavier elements. All the heavier elements are made in stars, so where did the helium come from? The answer is, it was formed in the first stages of the universe.

The first minute

There is a process called pair production, where two photons can create a pair of particle and antiparticles only if the energy of the photon is greater than the energy of each particle. There is this opposite process where a particle and an antiparticle collide and create photons. This process is called annihilation. For example, if a proton and an antiproton collide with each other with low velocity it can create two photons.

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Before 0.0001 sec these photons were so energetic that they continuously produced proton and antiproton. At the same time, the annihilation process was going on. But, after that time, the temperature went down and the energy decreased. So, these pair production stopped but the annihilation didn't. But in this process, a favour went to the side of the proton. Let us say, in one billion pair production gives half, a billion and one protons and half a billion antiproton. And in annihilation half, a billion and one proton and the half a billion of antiproton makes a billion photon and a proton. So all we are left with a few billion photons and some protons. As this photon is never going to be annihilated or produced, we say it is frozen out. As a neutron has the same mass as a proton, it freezes out almost at the same time. Electron being less massive it freezes out around four seconds. So, all there is only protons, neutrons and electrons.

The Second minute

After the second minute, the temperature became around 1.2 billion degrees. This is the temperature when photon energy is around 1.8 X 10 ^-14 joule which is actually the binding energy of deuterium. Deuterium is a heavy hydrogen which has one proton and a neutron in the nucleus. Photon of this energy can break deuterium in its original elements. But when the energy goes below that it can not be done. So, for the first time in universe some element complicated than hydrogen can exist.

The Third minute and the boring state of the universe

In the third minute temperature even gets lower. So, in this temperature photons doesn't have enough energy to break apart the deuterium nucleus. So, fusion goes on. Deuterion fuse with hydrogen and then neutron makes helium. It can happen even deuterium and neutron and then proton fuse into helium. The easiest way would be two deuterium fuse into helium. But during the early universe deuterium is so rare. So, it happens usually in the first way. Please remember that this is not like the p-p chain reaction in the sun like star. In the early universe free neutron can be found and their half-life is around 15 to 20 mins and they can decay to proton and a electron. In sun there is no free neutron running around. Helium can fuse with deutorium and create Lithium and then deuterium with lithium can produce berilium. But because of not abundance of deuterium, these atoms are rare. Neucleosythesis stops after the first half an hour and only first four light elements can be produced in this process. The neutron left over are mostly decay into proton and electron. Temperature goes down with time and makes the environment prepared for fusion reactions. Until 2500 years it stays like that. It can be called a boring state of the universe. Gradually with time the rest mass of the universe started coming closer gravitationally and started dominating over photon radiation. Around 400000 years electrons and neucleus came together to form atom. This is how matter was completely separated from radiation. The radiation left over is known as cosmic background radiation.

Formation of structure and Acceleration of cosmos

With time there is created places where matter was denser than other places. Then this denser places started attracting matters nearby gravitationally. This slowly created the formation of gas clouds, stars, galaxies and what we observe today. If we want to enter into the details we have to see what kind of the matter exist in the universe. Four possible matter we know of which is cold dark matter, warm dark matter. hot dark matter and baryonic matter. From the best measurement possible we know the data matches more with the cold dark matter and 23 percent of the matter in the universe is of this kid and 4.5 percent is baryonic matter.

Evidence from cosmic background radiation and supernova type 1a directs toward possibility of a unknown and mysterious form of energy, we call it the dark energy. As we predict 73 percent of energy of total universe is dark energy. The baby universe was filled with dark energy but as there was less space and matters were closer so gravity dominated. As time passed by and dark energy was slowly pushing the universe towards expansion and increase the acceleration rate of expansion. In the next post I will talk in details about dark matter and dark energy. So, If you like this post stay tuned for the next post as well.

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Will it expand forever

The universe is expanding that is for sure as we see all the galaxies are moving away from us as it can be also proved by the red-shift we observe. It doesnt really put us into the center of the universe but we will always see if a galaxy is moving away from us if that is not in the same cluster group. Now, the question is will it expand forever or it will stop? Well, the answer depends on the density. if the density is large enough it is going to collapse in a big crunch. This is called the closed universe. But if density is smaller it would go on expanding forever. But if it goes towards to a critical value of density then it will approach to a zero expansion rate and will never collapse. This density parameter is given by Omega. When its value is 1 it represents the critical density. Now, if we really want to know at which speed a galaxy is moving away from us that answer was given by Edwin Hubble. It is known as Hubble's law (). Here v is velocity, H is Hubble's constant and d is distance. What it says is, velocity determined by red-shift is directly proportional to the distance of the galaxy. I am leaving a graph down to see the co-relation

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Conclusion

We live in a mysterious universe. It has been always a question of mankind who are we? where we came from? Although in the beginning they were philosophical questions but science took its place and try to come up with evidence and proofs to answer those question. Theory of big bang and nucleosythesis at least give us the answer of origin and how everything formed. Universe has its layers like onion and but with technological advancement and science its possible to peal its layers and answer the unknown. Thats all for now. I would love to know about your opinion in comments.

References

1. Simon Singh, Big bang: The origin of universe.

2. General Astrophysics, Olga Atanackovic.

3. Ohio-state.edu

4.Wiki