The Universe is all that we can see, not only with our eyes but also with the help of telescopes. We know that space is very vast and our Earth is just like a particle of dust.
Has it always been like this? How did it start? There are many questions that put us in trouble. Till middle of the 20th century scientist thought that our universe is ageless or infinite and it was and always will be. Then Einstein’s theory of relativity gave us better understanding about gravity that will help us to understand the universe. Apart from Einstein, Edwin Hubble (the famous astronomer) has also given his contribution. In his exploration, he notices that all the galaxies are moving away from each other at an increasing rate. And predictions were made about it earlier, which were seen in reality and after this , in 1954 big bang’s biggest evidence – Cosmic microwave background radiation( discovered by scientist ) Because the big bang theory indicates that the universe was very hot in the beginning stages and the whole Universe had the same color ‘orange’. There were at very high temperature super charged particles present in the universe. At that time the temperature was so high that electron and proton could not make an atom together. These ionised particles are called plasma and plasma also emits electromagnetic waves. But because the neutral atom was not present at that time and the universe was very dense, these light particles could not travel very far because these particles were trapped between electrons due to the scattering effect. Now over time the temperature of this plasma started falling and the temperature came down to 300k. Then neutral atoms were created and the universe was almost transparent too. Now the orange light particles of plasma could travel in the universe, but here comes the question that if the color of the universe was orange then why do we see black?
As we know that the Universe is expanding and the expansion of the Universe stretches the wave of light (this is called cosmological red shifting) so now over time , these orange light particles were stretched and convert into red and then red to infrared and now after 3.8 billion years of expansion it converts into microwaves ( so we can not see through our naked eyes ) Because of this we see space as dark black. By observing these microwaves, we have created a picture of the Universe which is seen as cosmic microwave background and this is not a picture of the galaxy and stars, this is rather the picture after the big bang.
Then after that many advanced technologies like hubble telescope which gave us lots of evidence of big bang and also the big picture of the universe. Some observations also show that our universe is expanding.
But a question always comes to mind that if there was nothing before the Big Bang, then how is everything possible and how did it become such a huge universe? So let’s know how this universe started.
Now first let’s ignore what happened before the big bang.
So basically this big bang is not a blast, but it was a type of rapid expansion of space That means space started expanding at such a speed that in a very short time, a small thing made a big world. So basically the entire universe was compressed in a small dot-like area before the Big Bang. All matter and energy were compressed in that area which was very dense.
Now what happens next will be in a very short time ( less time means in trillionth of trillionth of 1 second ) which the brain of humans cannot even imagine. Now the universe started expanding rapidly in this state to the size if a football, this stage is called inflation. This inflation stage of the big bang was done in 10^-35 part of a second later. These numbers show that all this happened in a very short time so In this stage only space was expanding and not the universe and the universe has no boundaries but there were boundaries of space and they were expand rapidly.
That football-size universe was very hot and dense and Inside it was filled with energy in particles that existed for very little time this means that they were constantly created and were also destroyed in a very short time. Gluons that hold the nucleus of the particles were constantly breakdown into pair of quarks who went ahead to destroy by each other by giving out more gluons. Likewise, quarks were formed by combining pairs of quarks and gluons again. So as Einstein pointed out, Matter and energy were no just equal in theories but the temperature was so high that they were practically the same. At the same time matter won in the clash of anti-matter. So today we can only see matters and anti matters does not exist at all. This happened because some how at the time of the big bang one billion anti-matter particle for one billion matter particle. Now about 10^-9 seconds later natural forces was born instead of the massive ultimate force, many of refined versions have been created who use to facts on different rules
Today we call these forces – 4 fundamental forces of nature.
3 Weak Nuclear Forces
4 Strong Nuclear Force
So by now, the universe has become a billion kilometers in diameter in this part of 1 second due to which temperature began to decrease.
So the cycle where quarks born and convert into energy is also stopped. In 10^6 quarks were combined to become hadrons (like neutron, proton) and leptons (Electron).
So by now, the universe has cool down because it has become a hundred billion kilometers in diameter. In this state of the universe, it is now possible that most of the neutrons can decay to become protons which give birth to the first atom of hydrogen. After a few minutes, its temperature cooled down further and things settle down. atom formed in search of stability and hadrons (Neutrons and protons) or leptons (electrons). All atoms were atoms of hydrogen gas at this time. Due to which, this period is called the cosmic dark age because no stars was born yet and hydrogen gas was not allowing any visible light particle to pass. Then hydrogen gas began to concentrate at one place till the millions of years because of the pressure of gravity and because of this the birth of star started. Now due to the passing of radiation of stars. hydrogen gas started bringing light particles out into the universe. SO this is how light came for the first time is how light came for the first time in the Universe and even today, start is able to emit light for this reason, then because of the stars, the solar system was also born! and because of their energy, light also became possible. So it was a journey from the big bang. But some questions still cannot be answered. Like why did the big bang occur? What existed before the big bang?
It is not possible to answer these questions yet, Because before the big bang, All the laws of the the Universe Stopped Working and even time also.