We
have heard from our childhood that the universe is expanding, or in other
words, the cosmic objects in this universe are gradually moving away from each
other. Then it can be said that there was a time when all these objects came
together. We can say that through the process of separation of cosmic objects,
this universe has been created. This thinking introduces a new scientific
theory as well as model in the field of cosmology which we have identified as
the Big Bang Theory. Let's try to understand this in very simple language.
There
was no end to the curiosity of ordinary people, especially scientists, about
how the universe was created. In 1912, while observing a spiral galaxy by
American astronomer Vesto Slipher, he noticed that it was gradually moving away
from the earth, and later he saw this feature in almost all the galaxies
visible from the earth. However, he could not understand the subject properly.
In 1922, 10 years after this event, Russian cosmologist and mathematician
Alexander Friedman showed through a series of equations from ‘Field Equations’
a part of Albert Einstein's General Relativity Theory that space was expanding.
In the meantime, American astronomer
Edwin Hubble, through long research, has proved the expansion of space through
his famous 'Hubble Principle'. During this time various scientists have
presented their doctrines to us. Notable among these theories are Arthur Milne's
Milne Model, Richard Tolman's Oscillatory Universe Hypothesis, Fred Hoyle's
Steady-State Hypothesis, Fritz Zwicky's hypothesis and so on. Of these,
Belgium's Roman Catholic missionary George Lemaître's Big Bang Theory (then it
was Big Bang Hypothesis) is considered to be the most appropriate in terms of
the various events that took place in space, and this theory has been accepted
worldwide as a suitable explanatory theory for the creation of the universe.
Although this theory came to our notice in 1927, it was named by Fred Hoyle in
1949. The term 'Big Bang' was first published in ‘The Listener’ magazine. Sometime
later, Lemaître's theory of the Big Bang came to fruition, based on some
theories by George Gamow. The Big Bang theory was further established in 1964
with the discovery of Cosmic Microwave Background (CMB) radiation.
Before
starting the main discussion, the two major misconceptions about this theory
should be mentioned. Many have the misconception that this theory or model can
provide a complete explanation of the origin of the entire universe. But the
reality is that this model only identifies the observable universe which is
only a tiny part of the entire universe. The second biggest misconception is
that this theory explains everything in the universe, but in reality it does
not explain exactly how energy, time and space came into being.
According
to the theory of the Big Bang, the universe was formed from a very dense and
heated state about 1,375crore years ago. Further analysis suggests that the
entire universe originated from an ancient point, having infinite density and
gravity, with a terrifying explosion. This point is called ‘Cosmic Point of
Singularity’. The size of this point is less than the protons in the nucleus of
the atomic nucleus. This explosion created the time, matter and four
fundamental forces (Gravitational force, Atomic strong force, Atomic weak force
and Electromagnetic force) and our universe began its journey. However, it is
not yet possible to say exactly what happened before this situation. However,
some theories have proposed ‘Cosmic Singularity State’ to explain the period
before this explosion.
Exactly
after the Big Bang, that is, 10-43 seconds after the creation of the
universe, the conventional laws of physics in the universe gained their
effectiveness. After 10-35 seconds of this time the cosmic bulge
starts and since then the universe has started to expand and it is still going
on. As the size of the universe increases, so does its temperature decreases.
At some point during this temperature drop, the particles in the universe begin
to break down and elementary particles are formed. The cooling process in the
universe results in a decrease in the relative velocity between the particles.
Sometime later, protons and neutrons combine to form the earliest elements of
the universe. Some 3,80,000 years after the Big Bang, electrons and nuclei
combine to form the true atom of matter, and the hydrogen atom is formed. As a
result of this phenomenon, some amount of energy is separated from matter and
spreads around the universe through radiation which is called Cosmic Microwave
Background Radiation. This is the last ray of light produced by the Big Bang
that still exists. But in the hundreds of thousands of stars and planets
illuminated by the light of those stars and the light reflected by that planet,
that ancient cosmic dim red ray cannot be found.
With
the expansion of the universe, the distribution of matter was not equal
everywhere, resulting in inconsistencies of matter in the universe. Basically
galaxies, stars, planets, satellites, comets, meteors, etc. were formed where
the density of matter is higher. Where the amount of matter was low or
non-existent, a huge area-wide void was created. These regions contain very
small amounts of cosmic matter. This region is called Cosmic Void. Our solar
system is in such a gigantic cosmic void, called the KBC Cosmic Void. (Links to
details of cosmic void are given: https://spacejagat.blogspot.com/2020/02/c-osmicvoid-literal-meaning-of-these.html )
At that time, there were basically three types of matter in the universe which
still exist, namely cold dark matter, warm dark matter and baryonic material.
Here baryonic matter refers to those substances whose existence can be directly
understood. About 80 percent of all these substances were cold dark matter. In
addition to all these substances, radiation and various kinds of energy existed
in the universe in various forms then and still do. The most mysterious of
these is dark energy.
Although
the cause of the Big Bang is not yet clear, there are some reasons and evidence
behind the worldwide acceptance of this theory. Let us first take a look at the
principles of this theory.
1. Universality
of Physical Principles:
Physical
principle or scientific principle or natural principle is a kind of scientific
general concept which is formed through the practical observation of the
physical behavior of matter.
2. Cosmic
Principles:
According
to this principle, space is homogeneous and isotropic in the measurement of
distance (Isotropic: The physical property for which the numerical
value of a substance becomes same when it is measured from different angle)
3. Copernicus's
Principle:
This
principle states that neither our earth nor our solar system is at the centre
of space.
Now we will look at four of the biggest
proofs that the Big Bang really did happen in the past.
1.
Hubble's Principle:
According
to this principle, the red shift of distant visible galaxies from the earth is
taking place and this phenomenon is proportional to their distance from the
earth that means the farther a galaxy travels from earth, the longer the wavelength
of light emitted with the lower the frequency. In the case of visible light,
the light with the longest wavelength and the lowest frequency is red, so light
from distant galaxies catches our eyes as red, and the phenomenon of distant
galaxies is called Redshift. This phenomenon proves that cosmic objects are
gradually moving away from each other from a dense state. This event refers to
the Big Bang because matter has been moving away from each other in the
universe ever since.
2.
Cosmic Microwave Background Radiation:
The
atmosphere was extremely hot before the Big Bang and the matter was in the
plasma state. At that time thermal equilibrium was maintained. But after the
Big Bang, the temperature began to drop rapidly, the atom was formed, and the
emission of energy from matter began to occur through radiation. Again, as a
result of Hubble's principle, the radiation took on a red color to move matter
away. That light scattering is still going on. So if on a dark night all the
stars in the sky of the earth and all the light reflected from the planets,
satellites, asteroids shining in the light of those stars could be resisted in
any way, it would be seen from one end of the horizon to the other that the
whole sky will be filled with soft, dim red light. It is this dim light that
bears witness to that great explosion of the past. Two spacecraft, COBE (Cosmic
Background Explorer) in 1989 and WMAP (Wilkinson Microwave Anisotropy Probe) in
2003, were launched for extensive research on the subject. The information sent
by them supports the theory of the Big Bang.
3.
Abundance of Primary Elements:
The
basic elements of this universe are hydrogen and helium and their various
allotropic modifications. Their nuclear fusion has created other elements. The
abundance of these primordial elements is a clear proof of the theory of the
Big Bang because it has not been possible to explain the abundance of these
primordial elements with the light of any theory other than the Big Bang alone.
4.
Evolution & Distribution of Galaxies:
The
first galaxy and quasar formed 1 billion or 100 crore years after the Big Bang
(Quasar: It is an extremely luminous active galactic nucleus, powered
by a super massive black hole) then formed the galactic cluster. Over time,
those cosmic objects began to age and began to evolve in various ways. So new
or near galaxies are different than distant or old galaxies. This evolution of
galaxies and their position indicates the Big Bang.
The
Big Bang may have solved the mystery of the creation of the universe, but it
has given rise to many questions that have yet to be answered in the world.
Here are some of the unresolved issues:
1.
Dark Matter:
Observations
over the last few decades have shown that the apparent force of the gravity in
the galaxies of the universe and the space between them is so great that it is
almost impossible for visible matter to supply it. The existence of dark matter
is thought of when thinking about this subject. But the idea was somewhat
inconsistent with the observation of various cosmic phenomena, but evidence of
the presence of this substance was found in various phenomena. Although cosmologists
were initially skeptical of the substance's presence, they have since confirmed
the presence of the substance after the year of 2006. The most important thing
is that this substance, like all other substances, is almost impossible to
identify directly. So this matter has remained a mystery today. (Here is a link
to know more about Dark Matter: https://spacejagat.blogspot.com/2021/11/dark-matter-most-mysterious-particle-of.html)
2.
Dark Energy:
Extensive
statistics on the total energy density of the universe in the last decade of
the last century have shown that no suitable scientific explanation can be
found for more than 70% energy density. From this came the idea of invisible
dark energy. Although research has been done on this subject by sending various
satellites into space at different times, this aspect of the Big Bang theory is
still a mystery. (Here is a link to know more about Dark Energy: https://spacejagat.blogspot.com/2021/10/dark-energy-master-of-universe.html)
3.
Barionic Asymmetry:
The
universe was initially very hot. Since then, the universe has been cooling
rapidly. But it is not yet understood why the amount of antimatter has
increased in this universe more than matter. (Antimatter: The
substances which are similar to ordinary matters but they differ only in charge.
For example, the antimatter with the opposite charge of an electron of equal
mass is positron) The amount of these two types of matter was equal in the
universe when heated in the past, but it is not yet understood why such an
inequality is observed in the present.
4.
Horizon Problem:
There
may be nothing in this universe faster than light, but the temperature of
cosmic microwave background radiation is numerically equal to the temperature
of our nearest space at two farthest places in the universe from which light
can no longer be seen by observers. Although this thermal equilibrium is true,
its causation is not yet understood.
There
are many other cosmic issues beyond which we do not yet know the answer, such
as the problem of equilibrium, the phenomenon of the magnetic pole, or the
traditional question of why the Big Bang happened. Where did the Cosmic Point of
Singularity come from? How did that point come about? What is the environment
of the place where the point was located? Is there more point like that? What
is the relationship of the Big Bang with the Parallel Universe? Etc.
Now
another question that often comes to our mind is what is the consequence of the
cosmic matter moving away from each other or the universe expanding as a result
of this big bang? Before the discovery of dark energy, scientists thought that,
either after a certain period of time the expansion of the universe would slow
down and stop completely and the opposite incident would happen that means the
universe would begin to shrink and return to its former hot and dense state or
if the expansion of the universe does not stop completely, it will become
extremely slow, the density of cosmic objects will decrease, the average
temperature of space will decrease further, the black hole will begin to
evaporate and the occurrence of Big Freeze in the universe will cause Heat
Death.
But
after the discovery of dark energy, it is said that as a result of the
expansion of the universe, distant cosmic objects will at some point move
beyond our observations, meaning that from there the light will no longer reach
the observer's eyes or, in scientific terms, all these objects will at some
point cross the Event Horizon. However, it is unknown, at this time, to us that
what would be happened then. According to another doctrine, all the galaxies,
stars, planets, satellites, etc. of this universe will be shattered due to
expansion and this incident may lead to Big Rip (Link provided for details on
the Big Rip: https://spacejagat.blogspot.com/2022/01/are-we-proceeding-towards-big-rip.html)
One thing that has become clear in discussing various issues is that the Big Bang did not fully visualize the entire past of this universe. The Big Bang is only a small part of the events of that past because the answers to many unresolved questions are still unknown to us. With the help of this theory, some scenario has been revealed but there may be something more out of the picture presented. In order to get detailed information about all these subjects, it is necessary to take the formulas of different branches of physics together and make a standard model by applying it. Who knows, maybe more interesting information is waiting for us on the other side of the closed window. Only the time, created by the Big Bang, can tell us how far we can go in this regard.
DECLARATION: All The Images Have Been Sourced From Google.
