The Greatest Question?- "How do we even know that Big Bang has happened?" part 1

We go on through our day-to-day lives almost even without noticing some of the core questions that is tricking our humanity's brain since from beginning. That is, why is something instead of nothing or why are we here? Or what it would mean if we truly unlock all the mysteries of universe? Is it even necessary to reach the ultimate destiny and what do we mean, if we unlock the theory of everything? These questions are truly mind boggling and really we don't have a answer to them. Let's envisage them at closer look like never before.

These blog posts' series can contradict your initial thoughts about something and even let you wonder about the greatest question. Be ready for it!

Introduction
         I have been going throughout the book of Stephen Hawking, "A brief history of Time", where I met with my extreme curiosity and amazement in the fields of astrophysics. So, there, I read about different kinds of stuff and it was truly fascinating. The first few words of this post have also been taken from the words of Carl Sagan introducing the book, A brief history of time. 
         Our speculations and imaginations have been truly amazing since the dawn of humanity, even when we just evolved from monkeys, which lead us to conquer the deepest questions of the universe. A few of the question we became able to conquer over them but we should also acknowledge ourselves that a vast cosmic ocean about the different questions is always left to be unravelled. Let's take a look at those questions and let's sort out of them as, The greatest question...........!

1. How the universe got its existence?
        Believe me or not, we are only given some, tiny footprints of our universe describing whether the universe has a beginning or not. With some existing clues, we tend to increase our ideas and with those ideas, we come to the conclusion. Some folks tend to hyperbolize these clues of Nature as Story is being told by Mother Nature. But lemme tell you, "Science doesn't depend upon one's saying, it needs proof and its significance."

Have a quick look back to Big Bang Theory

             Up and until, when Georges Lemaitre hypothesized Big Bang Theory in the year 1930s. he was mocked and disagreed by a large group of physicists including Albert Einstein. But when Edwin Hubble started observing something extraordinary happening in the cosmos and revealed his discovery of the expansion of the universe through reddening of the spectrum of stars of another galaxy made of same elements as of our galaxy. It was really the most absurd declaration of the 20th century which boggled the mind of every astronomer as well as physicists. It was somewhat like never-thought like experience to some of them. 
     At the time, in the 1940s, again, the concept of Big Bang came to light with the interpretations and solutions of General Theory of Relativity by Alexander Friedmann. As Big Bang Theory's concept got coincided with Hubble's observations. Later on, when some of the scientists like Ralph Alfer and George Gamow, took their interest to further proceed the journey of Big Bang. They published a paper regarding 'Big Bang Nucleosynthesis' popularly known "Alpher-Bethe-Gamow paper." In this paper, they provided a backbone to this theory by raising the term, 'Big Bang nucleosynthesis'. 
    They argued that Big Bang would have produced an infinite amount of matter and energy and as space expanded, subatomic particles coalesced to form Hydrogen and when given enough heat like in the cores of stars, hydrogen can fuse into helium. This discovery explained about the abundance of Hydrogen and Helium which was a riddle to contemporary astronomers as when they looked around in the cosmos and they used to observe an abundance of hydrogen which makes up three-fourths of visible cosmos. And again, helium was observed as the second most abundant element in the universe. This nucleosynthesis was successfully pointing towards Big Bang Theory. 
    We have seen two evident, elegant reasons that why should we believe Big Bang. Now let's move further:
        Our scientific society in the age of 1960s became a hypocritical and two-faced monster because some folks believe in Steady State and some believe in Big Bang Theory. (In the previous post, I have explained everything about so. Go and check it out) The famous physicist, George Gamow (who was orthodox supporter of Big Bang Theory) predicted that "There may be a phase of universe when universe was too hot that light emitted would not come out due to ultra-high density but when universe would cool, due to expansion, much enough then, it might have released photons that should be called as 'afterglow of Big Bang'. With the calculations, he found that photon that was released after 380,000 years after the bang was of ultra-high frequency or gamma photons that have travelled across the spacetime and reach to us then due to expansion, their wavelength might have increased causing to shift to microwave spectrum. This was hypothetically named as, 'Cosmic Microwave Background'."  

Penzias and Wilson Microwave Detector

That was the same thing, what Arno Penzias and Robert Wilson accidentally detected. That was a relic of the Big Bang and this was a big thing that can't be ignored by anyone. With this, steady state theory got its final blow as it got confirmed that universe was not same as in earlier times, despite that, it was hotter, smaller and compact.
     The far more idealising reason why we believe in Big Bang could be, Absence of multi-wavelength quasars. You would probably ask, how actually? 
       Let me clear one thing that the farther we look in space the paster we look in time as we detect events with light which is considered as an absolute measurement and speed of cosmos. This is how we correlate space with time. Now, as you asked, why can't quasars exist around ours? Firstly, let's take a look, What's a quasar?

Artistic Depiction of Quasar

    Quasar, by its definition, is simply a galaxy with extreme luminosity due to super active galactic nuclei. The far we have observed, we always observe a supermassive black hole which makes a galaxy to stabilize. When a star passes around it, generally due to its immense gravitational pull, it attracts its matter, generally in the form of plasma, and eventually devour the whole star and when it starts feeding the matter, it becomes violently spectacular which makes it fatal for all life forms as it releases x rays and sometimes, gamma rays and super relativistic jets or cosmic rays too. As it feeds on, its mass increases and eventually event horizon grows up even larger. Here's a short clip if you would like to know how and actually what happens when it happens:

If we look upon a quasar, then we can say that in a galaxy where matter is packed in a congested manner and when a supermassive black hole stays at the centre, as it's obvious, then it is probable that it would continuously devour all the matter releasing an immense amount of high energy radiation. But when we still look all around to find any of these active galactic nuclei galaxies, we don't have got any of them. They only seem to exist very farther distance that is about billions of light years far. That means only billions of years ago, quasars were persisting in the cosmos, as this statement was also manipulated by Big Bang Theorists, then they tried to add their answers to this, 'As universe was that time, too hot, too small and too compact that galaxies were existing too close to each other.' 
    By this cause also, Big Bang was supported and become reasonable that 'why should one believe in Big Bang?'.

        Now, let's take a look at another reasonable question by which two marvel theories of gravity of its times, have got it wrong, that is:- Olber's Paradox

Why the night sky is so dark?
Can't they be enlightened by infinite stars?

            Have you ever wondered, even in your childhood, why is night sky so dark? Only miserable stars with its twinkling bright along with asilent moon and some planets. Why not our night sky even look brighter due to stars twinkling like on each and every section of sky? Why not our night sky receive infinite amount of radiation due to infinite amount of stars as many of the uprising scientists like Johannes Kepler said that our universe is uniform and infinite?

Let me explain it..............!
        If we start gazing at any point in the night sky then as the universe is infinite then our line of sight must have the possibility that it must require that a countless number of stars would fall in that line of sight only. This simple analogy unravels and questions so much about nature of the cosmos. To answer this, one simple answer might be maybe the light from other stars might have been blocked by dense clouds and nebulae. But think yourself only, if that cloud would become bombarded with radiation from stars, that we have assumed to be invisible, then it would also glow with a glare like a surface of a star. 
     Another reasonable statement passes out that as the universe is so vast and as distance increases, the intensity of light too decreases. Well, it's true but it's not the current reason we were asked for. With this answer, we would tackle only those who don't think about something too deeply. Because, if the universe was stated as uniform and infinite then distances would have been cancelled out due to infinite number of stars jiggling, flickering and twinkling all over the night sky.

So, what was the correct answer to this riddle?

The solution to this riddle was solved by Scottish physicist Lord Kelvin in 1901. He reasoned that when we look at the night sky, we are looking at it in the past, not as it is now because the speed of light is not instantaneous. He calculated that for the night sky to be totally white with twinkling stars, the universe would have to extend hundreds of trillions of light-years. But because the universe is not trillions of years old that's why the night sky is black.

Or

The second contributing reason to this paradox came out to be, because of the finite lifespan of stars, which is generally measured in billions of years only, not trillions.

       

"The universe is not only queerer than we suppose, it is queerer than we can suppose."

The concept of the idea of Big Bang Theory relies on the scientific method of speculating something and then we predict something and when it matches with our observations, we proceed the theory even further. This is how Big Bang hypothesis came into criteria of theory in the era of the 60s, by the prediction of Cosmic Microwave Background (which I suppose to be the whole backbone and evidence of Big Bang Theory). At that time, physicists all over the world debated with the data which was earlier derived from Alexander Friedmann about the fate of the universe. There was a vigorous debate going on in the world of Astronomy whether our universe would die in Big Crunch or Big Freeze? There at the same time, a new theory came out by MIT Graduate Alan Guth which was named as, "Inflationary Theory".

Alan Guth

Let's have a case study on it..........!
     The idea of hyperinflation was a revolutionary and fully debated concept and actually, it supports big bang theory. But as a lame person can help another lame one, just as this Inflation theory was proposed as a hypothesis but as it reveals and solves some key concepts which were trickier to understand. One of the major problems it has tackled with was Flatness problem.  The standard picture of the big bang could not explain why the universe is so flat as it seems.The inflationary theory was a groundbreaking one for those who thought physics was a nice place to visit. Because it totally depends upon quantum mechanics uncertainty principle. We will see how?
      Astronomers (at the time before the proposal of Inflationary theory by Alan Guth) observed that the universe's curvature is remarkably close to zero and they even surprised by that. Guth explained that universe underwent vigorous inflation of space and time with speeds much more than the speed of light, he also reasoned that Big Bang was not something like supernovae or hypernovae explosion but it's the inflation of space and time itself which gave birth to the universe as we perceive. He speculated universe as a balloon that underwent hyperinflation at the instant moment when time, as we know of it, started with a bang. He speculated that we along with our long-range telescopes we were just like microbes present on it. To us, the universe seems to be flat (that's not mean like 2D paper, it's 4D spacetime seeming to be flat) and the grand picture is different. Inflation has stretched space-time so much that it appears flat. The major reason why should we refer inflation to Big Bang Theory is that of its involving of the physics of extremely small i.e. Quantum Theory as well as Standard Model. It even tries to approach the quantum uncertainty principle which states that any fluctuation in spacetime could be devastating which might have led to hyperinflation.
       Not only did the inflation explain the data supporting the flatness of the universe, it has also solved Horizon problem.

     Again the question arises from simple realization that the night sky seems to be relatively uniform, no matter you look. You simply take a smallest patch in night sky and observe the amount of matter and comapare it with another patch of night sky. You would be surprised that it is the same density all over there. But, how is that even possible if nothing can speed up faster than light so how information travelled so much accurately all over the night sky? It is really tricking thingwhich really needs consideration.

Just look at this picture, what you see, is our baby universe when it was become transparent or in simple words, photons could travel to us as in form of microwave radiation. It is a map we have got by the data of Planck telescope which sensed the microwave radiation to which extent that we can see the density of matter occupied in the universe. Hey, did you observe something? Something extraordinary?
      Yeah, it is uniform in the density even when you look at it, you are seeing matter which is thousands of degrees Celsius and why is matter (generally in the form of plasma at that time) so even distributed to each region of space-time?
Let's have look at it!

The picture, you saw, in that, the place where it is depicted as red that means there is a huge clump of matter is present which is releasing radiation much hotter than blue ones. Somewhere, there is totally blue region which is depicted as devoid of matter or at least less amount of matter is there. You will wonder that, these matter are seeds which would collapse to form generation 1 stars and first galaxies but it might never have been formed until there is a rapid expansion which would even cool down the universe as density would decreaset for the formation of cosmic structures.

So, let's come to the point, when you look in the two opposite end of this cosmc microwave background picture, you will see they are uniform. But according to the calculations from the big bang theory, these opposite might have been separated by 90 million light years because of the normal expansion of space-time theorized by Georges Lemaitre. But there is no possible way that light or information could have traveled by 90 million light years in just 380,000 years. This was even more trickier than flatness problem. Alan Guth's Inflationary theory come into this situation and explained that at the moment after just big bang happened, hyperinflation had started extend the size of universe at unbelievable rate much more faster than light as space-time is not as any particle with a rest mass. This inflationary theory is really beautiful!

But one question, Alan Guth has also been trickled with:
How to stop inflation and what actually created such hyper-expansion of the universe?

Whatever that is but currently, we have our most suspectable culprit that is Dark Energy and really we don't actually know about it. That makes it so dark as we named it. ;)

Conclusion and What's next?

We have seen again how the Big Bang Theory came into existence and what's so special about it? The answer is nothing's special but it's only matching with our observations and speculations till now. While making this post, I have also taken help from book of Michio Kaku, Parallel Worlds, there I have read that, Big Bang Theory is so far correct with our calculations and observation and even every questions' answer can be derived from it. One day will sure come, when some loopholes maybe detected out in observations which won't fit well with Big Bang Theory then it will be probable that we will again either redefine our understanding or totally revolutionize our understanding of the universe. Really, I am also a big criticizer of it and I am also glad to be so because when we criticize something we even try to find loopholes in it, that's what I'm trying to do. This post has been precious to me and yes, it's created by me in only one week with continuous thinking and by placing humour in it too. But if you've got any misunderstanding in any of the concepts, I can explain it to you even more elaborative way. in future, I would try to make my posts more informative and humourous too so that you will get to the concepts more easily. Thanks for visiting us!