The Big Bang Theory(Birth Of Universe), explanation & significance by askerweb

The Big Bang Theory

Introduction Of The Big Bang Theory:

from the particle to the galaxy, everything space, time, and life is nothing but the universe. It means these all didn’t exist before the universe i.e. it all came with the universe. But now the question is how did the universe come?
well, there are several theories and myths regarding the creation of the universe. But the most accepted explanation is the Big Bang theory.
what is it?
It states that the universe began from a hot and infinitely dense point. After the explosion of it the all matter, energy, space, time created. In simple words, it states that the universe as we know it started with a small singularity(almost similar to a supercharged black hole). then inflated over the next 13.8 billion years to the cosmos that we know now.

Types Of Universe:

Before starting we should know a key point that there are two types of the universe :

  1. The observable universe that we can watch and in short the part of the universe till known to us,
  2. The unobservable universe beyond our vision, in short, the part of the universe till unknown to use or will be discovered in the upcoming future.

here we naturally will discuss the observable universe, with times it becomes bigger.
Our known universe is expanded with a radius of about 93 billion light-years.

But the question arises here is that “If the universe took birth just 13.8 billion years ago from a little tiny entity( we can’t say it a particle. Because it is assumed that before the big bang there is no particle. So we use the “entity” term here), then how it becomes 93 billion light-years in radius wider?

in short, the answer is expanding, which is the basis of the Big bang, It suggests that the universe till could not leave the effect of the big bang.

Inflation, accelerating expansion of universe, The Big Bang Theory

Why the name is such horrible, “Big Bang”?

It was 1927, Georges Lemaître, a Belgian priest first suggested the Big Bang theory in the 1920s, when he theorized that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble’s observations that galaxies are speeding away from us in all directions, as well as from the 1960s discovery of cosmic microwave radiation—interpreted as echoes of the big bang—by Arno Penzias and Robert Wilson.
However the theorem was based on Einstein’s GTR, but the main answer is Fred Hoyle’s Steady State Model, in which Hoyle stated that the universe is not expanding, the empty spaces between the universe are filled up with newborn matter, he named it as “Dark Matter”. He humiliating Lemaître’s theorem called it “Big Bang”. After that, it was a long time since the Scientist community splits into two groups. But after years spending and much research we found many proofs for Lemaître’s theorem and from then keeping the name unchanged we agreed with the “Big Bang” theory.

There are several proofs regarding the “Big Bang”. We will come back later.

Let’s start the explanation of the theory:

  1. At first, there was nothing but a small entity smaller than everything we have known till now and extremely hot and highly dense. The singularity idea was based on Einstein’s General Theory of Relativity. One theoretical physicist of Caltech, Sean Carroll said, “There is no reason to believe in GTR in this regime. It is going to be wrong to avoid or not taking into account quantum mechanics because in such a place of History of the universe this topic is very important & relevant. “
  2. Due to an unknown reason, the entity burst with more speed than light and the explosion of the energy, and the matter spread everywhere.
    N.B. It’s still unknown what happened before the Big bang. As there was no existence of time before Big Bang, the question is not completely right. Because at the same sense


Due to expanding the currently born universe became low dense and due to this it became cooler and the little particle crowded and created a high-density soup. The accumulated matter is called Blob.

expansion of universe, The Big Bang Theory


After the explosion a storng force expanded the universe ! billion times wider. This is called Inflation. Inflation is the bang of the Big Bang. Before it the universe was a little bit of stuff, may be expanded with quite small speed. it’s inflation for which the universe became big because it actually accelerates the process. If you think inflation is the violation of STR, is not correct, because STR states neither information, nor matter can be carried between teo points in the space, but inflation is the expansion of the universe itself.

What is dark energy?

Dark energy is the cause of inflation. It keeps the expansion rate of the universe constant, rather than drop at all. As the universe getting bigger there is a high chance of energy density dropping, dark energy maintains it. Michael Turner named it unknown, the mysterious energy that expands the universe. The energy is temporary, soon through the process of reheating it becomes ordinary matter. The property of dark energy is that it is almost the opposite of Gravity.

Era, epoch, Inflation, The Big Bang Theory

History of universe after the Big Bang:

To discuss the universe’s evolution we devide it into two major stages:

  1. Radiation era
  2. matter era

Radiation era:

This era is made of smaller stages call epochs that occurred within the universe’s

The story can be picked up at about 10 to the minus 43 seconds, Planck epoch. see following…

EpochTimeTemperatureWhat happened
The Planck epoch<10−43 s
>1032 K
(>1019 GeV)
No matter existed at this time. There was only energy & combination or ancestor of four fundamental forces, super force.
the four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—were forged into a single force, but it is still unknown to us how a unified force works. To know this first we have to know how Gravity works in sub-atomic particle level, which is still beyond our current Science.
At the end of this epoch due to an unknown key event Gravity split away from the super force.
However, the temperature and pressure were so much that the detailed physical status during this time can’t be known.
The grand unification epoch,<10−36 s>1029 K
(>1016 GeV)
This epoch was named for 3 remaining unified forces of nature. This epoch ended when the strong unified force broke away.
Inflationary epoch,
<10−32 s1028 K ~ 1022 K
the universe
rapidly expanded. instantly it grew
from the size of an atom
to the size of an orange
The universe at this time was piping hot
and it churned with electrons,
quarks, and other particles.
Electroweak epoch<10−32 s(1015 ~ 109 GeV)During this epoch the last two forces,
electromagnetic and weak,
finally split off
The quark epoch,10−12 s ~ 10−6 s1012 K
(>100 MeV)
In the early universe there was not any atom, anything was nothing but very very small partcles, which was caleed Quark. This was of high density (almost 1 trillion trillion trillion trillion times of water)[1 trillion= 10^12]
energies were too high for quarks to coalesce into hadrons, instead forming a quark–gluon plasma.
The hadron epoch10−6 s ~ 1 s1010 K
(>1 MeV)
universe cooled down enough
for quarks to bind together
and form hadrons. There was an interesting existense named as antimatter, which was one type of image of matter. When it comes in contact with matter it was defeated and disabled, but due to this war many empty spaces in the universe created. And this is the reason behind non-existence of anti-hadron.
1 s1010 K
(1 MeV)
In this epoch due to interacting of Neutrino with Baryonic matter our observable universe was expanding upto 10 light years of radius.
Lepton epoch1 s ~ 10 s1010 K ~ 109 K
(1 MeV ~ 100 keV)
In this era Lepton & antilepton were in thermal equillibrium
nuclear epoch10 s ~ 103 s109 K ~ 107 K
(100 keV ~ 1 keV)
the protons and neutrons
underwent a significant change.
They fused and created nuclei.
And in doing so, they created the first
chemical element in the universe, hydrogen. From it later Helium-4, Helium-3, Helium-7, deuterium and lithium-7 created.
Photon epoch10 s ~ 1.168·1013 s
(370 ka)
109 K ~ 4000 K
(100 keV ~ 0.4 eV)
There was plasma of nuclei, proton and electron and the temperature was high enough for binding of electron with nuclei

Matter Era:

as the name suggests, the matter era’s defined by the presence and predominance of matter in the universe.

It features three epochs that span billions of years. The vast majority of the universe’s life span, and includes the present day.

EpochWhat happened
Recombination epoch1. Neutral atoms were formed as the electrons bound to the Nuclei. Thus created hydrogen & helium atoms dotted the universe with atomic clouds.
2. In the clouds the small pockets of gas had enough gravity to cllect the atoms within it.
3. For the first time the universe become transparent.
4. The universe become 42 million light years of radius wider.
5. The photons of the CMB(Cosmetic Microwave Background) originated this time proof of which we will find later.
6. This time the matter was 1 billion times higher densed with respect to todays.
the galactic epochThe atoms were collected by the clouds formed a cluster, which became the seedlings of galaxies. Inside those galaxies stars began to form.
the stellar epochMaking nest in the galaxies when the stars started to form, the epoch changed to the current stage or the universe’s development stage.
The formation of stars created a strong ripple effect which helped the universe to be formed as we know it now.
Due to the heat inside the stars there happens conversion of Hydrogen into Helium and vice-versa & in almost similar way remaining elements formed. These elements were building blocks for life i.e. planet, stars, etc.
Dark energy, The Big Bang Theory

What is Dark Ages:

After the great Big Bang, the universe utterly became dark (Though it was almost dark previously, we came back later if it was completely dark or not). This period before the first star was born is known as the dark ages. It was for several hundred billion years in our 13.8 billion years universe.

What happened after 3 minutes of the Big Bang?

within 3 minutes of the Big Bang, the protons and neutrons started fusing together forming Deuterium, from the combination of deuterium Helium-4 formed. In our modern universe what we see, all began to be formed after this important time, 3 minutes.

What is the Big Crunch?

We all now know that the universe is expanding with accelerating speed, but if it happens that the expansion stops & the universe started to compress, then what happened? all galaxy & stars attracting each other will cause a collision. If it ever happens, is called the Big Crunch.

What is antimatter?

Antimatter is the image of matter. When it comes into contact with matter results in collision & matter wins & antimatter disabled. Disabling means not the actually vanishing of matter, According to Einstein’s E=mc^2 the disabled antimatter transforms into the same amount energy. The ratio of the matter to antimatter is one crore one to one crore. So, I hope you will understand why there are many empty spaces created with disabling of antimatter.

Population III stars, first generation hypothetical stars, The Big Bang Theory

What is Population III stars?

In 1940 Walter Baade divided all stars into two groups:

  1. Population I (metal-rich, Youngest),
  2. Population II (metal-poor, oldest)

But the problem arose regarding the metallicities of the stars. Though the Population II stars were metal-poor but were not enough that we can say it oldest. The value of metallicities is not acceptable enough for any first-generation stars, whose births ended the dark ages because at that time there was no enough metal formed to show that value of metallicities. It suggests that the Population II stars may be older, but we can’t say it oldest. Then Astronomers introduced one new type of stars, Population III stars, made with primordial gas – hydrogen, helium, and very small amounts of lithium and beryllium.

But the problem is the Population III stars are still hypothetical & are not observed till now in spite of intense research.

So in short there are three types of stars:

  1. Population I(Youngest)
  2. Population II(Older)
  3. Population III(Oldest)

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