There are many things in the universe that make people curious about it. The main reason is the mystery of that subject. With the help of his patience and talent, human has torn the web of that mystery and has fulfilled his curiosity by knowing the inner mystical theory. But even after this, there are many things that exist, but the mystery has not been penetrated in any way. In discussing space, we will try to understand one such thing today, which is probably the most mysterious and almost entirely speculative in space science. Today our subject is Dark Energy.
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| Expansion of Universe |
In
the 1980's, American physicist Allan Guth and Russian cosmologist Alexei
Starobinsky first speculated about this energy. The first evidence of this
energy was found in 1998. At that time, the American scientist Michael Turner
named this invisible energy as Dark Energy after its resemblance to Dark
Matter. In 2011, Adam Rieses was awarded the Nobel Prize in Physics for
providing evidence in support of Dark Energy.
Even
after so many things, Dark Energy is a puzzle for us today. In space science,
this energy is an unknown energy that is probably affecting space the most. As
it has been said before, the maximum portion of what is said about this energy
is based on conjecture. There is nothing in that sense to say direct evidence.
This is an energy with which the only means of communication is gravitational
force because it works in contrast to gravitational force. To date, no research
has been done on this energy in the laboratory. If there is anything in
existence, it is just few models which are made through combination of physics
and mathematics.
In
order to get to know this energy, we need to know about the early stages of the
creation of space. Our universe was created by Big Bang on a tiny particle
(Point of Singularity). As a result of the explosion, matter (Hydrogen gas and
dust particles) began to spread rapidly. All these objects had come close and
formed nebula (birthplace of stars), galaxies, stars, planets, satellites,
asteroids, meteors, comets, etc. Initially it has been observed that an object
loses its momentum by moving for some time under the influence of kinetic
energy. But in this case, it has been seen that even after 1,380 crore years
after the Big Bang, that momentum has not decreased but has been increasing
over time. Observable space is also growing faster in volume than the speed of light.
At present, the expansion of space is about 9,300 light years instead of 1,380
crore. In other word, space is expanding at a speed of 5 times that of light.
Every object in space is moving away from each other. This is also affecting
our solar system. Every year the moon moves 3.8 centimeter away from the earth
and the earth moves 11 to 19 centimeter away from the sun. There are about 2
trillion or 2 thousand crore galaxies in space, each with an average of a few
trillion stars and countless planets, satellites, comets and meteors. All in
all, space continues to expand rapidly, ignoring the powerful gravitational
force, generated by enormous mass of the universe. From now on, scientists
estimate that there must be an unknown energy in all parts of the universe to
which gravitational force has been defeated for the past 1,380 crore years.
This mysterious energy has been given the name Dark Energy.
Since
this energy acts against gravity, it is called Gravitational Repulsion. The
Wilkinson Microwave Anisotropy Probe (WMAP Spacecraft) and the Planck
spacecraft cosmic microwave background analysis have yielded some important
information. It should be noted here that if it is possible to obscure the
light of all the stars in the sky, it would be seen that the whole sky is
covered in dim red light. This light is the last ray of light, created after
the Big Bang. This is called Cosmic Microwave Background. Analyzing that ray,
it is known that if our universe is divided on the basis of structural
elements, then it can be seen that the universe is basically made up of three
elements, namely Matter, Radiation and Dark Energy. We will put radiation aside
here and move on with our discussions. There are two kinds of matter here. The
first is Baryonic matter or perceptible matter from which stars, planets,
comets etc. have originated and the second is Dark Matter whose nature is as
mysterious as Dark Energy. As a percentage, their presence is 5 percent and 26
percent respectively. The remaining 69 percent is Dark Energy. Since most of
the elements of space is Dark Energy, so Dark Energy controls the space.
In
order to know about Dark Energy, we should have some basic knowledge about a
subject of physics and that is Doppler Effect. If the distance between the
source and the observer of the wave (both sound and light) is changed, then the
frequency and wavelength of the wave will change. This phenomenon is called
Doppler Effect. As the distance between the wave source and the observer
increases, the wavelength will increase but the frequency will decrease. When
this happens in the case of light, the visible light will turn red. The
phenomenon of the emergence of this red light is called Redshift in the
language of science.
When
a giant star in space breaks down with a massive explosion to run out of
energy, that state of the star is called a Supernova. Redshift has been
observed by analyzing this supernova. Its means that the supernova is gradually
moving away from us and the space is expanding under the influence of Dark
Energy. Since 2011, scientists have been observing millions of small and large
galaxies through the Australian Astronomical Observatory and observed their Redshift,
which has led scientists to believe that the effects of Dark Energy continue to
expand in space. Cosmic Microwave Backgrounds are seen in space, the last sign
of the Big Bang, probably due to the Redshift. Expansion of space has resulted
in the formation of a titanic Cosmic Void with an average radius of 150 Mega
persec in observable space (1 mega parsec = 32,61,563.78 light years). By Light
Year we mean the distance that light travels in a year. [Link for details on
Cosmic Void is given: https://spacejagat.blogspot.com/2020/02/c-osmicvoid-literal-meaning-of-these.html ]
This
energy with unknown properties is of great interest to scientists because
scientists believe that this energy can be used to redefine gravitational force,
to re-examine the observational data of space, and to know more accurately the
properties of Dark Energy. The simplest explanation of Dark Energy is that,
this energy is the underlying fundamental energy of space which is also called
Cosmological Constant because the strength or density of this energy is equal
in different places of space. Einstein proposed this Cosmological Constant to
overcome the difficulty of determining the gravitational formula for the unequal
distribution of matter in the universe. This Cosmological Constant is
represented by the Lambda symbol (λ). Only then, it has been possible to
express the expansion of space in a mathematical or practical way. Many people
call Dark Energy as Vacuum Energy.
Albert
Einstein's famous Theory of General Relativity predicted this long ago. (What
we perceive as the gravitational force expressed by General Relativity is
derived from the curvature of space and time) It is further speculated that
gravity may have caused the formation of Dark Energy and Dark Matter, and that
Dark Matter may have been eroded and transformed into new energy, Dark Energy.
Matter
and time appeared when the universe was created after the Big Bang. At that
time there was a kind of vibration between matter (hydrogen atoms and dust)
called Baryon Acoustic Oscillation. Scientists speculate that this Baryon
Acoustic Oscillation must be understood in order to understand the effects of
Dark Energy from the early history of the universe. Scientists are developing a
number of mathematical models to understand the Dark Energy through this
oscillation. Some such models are Chevalier-Polarsky-Linder Model, Barboza and
Alkaniz Model, etc. The varieties that have been modeled on this Dark Energy
are different from each other, so the predictions of the future here must also
be different.
Mathematical
analysis has shown that the origin of this energy was about 9 billion or 900
crore years ago, in the sense that space did not begin to expand at a
tremendous velocity because then the effect of this Dark Energy was not so
much. But the velocity of expansion of space has been increasing rapidly since
our sun began to form 5 billion or 500 crore years ago. Earlier, this energy
may not have had such an effect due to the gravitational force. During this
time, the amount of matter per unit area of space decreases rapidly,
resulting in a decrease in the intensity of the gravitational force. After that
the effect of Dark Energy increases rapidly and the volume of space doubles but
the density of matter is halved in every per unit area because there is no
change in the total mass of matter. Dark Energy became stronger than
gravitational force. At first, scientists thought that the concentration of
Dark Energy may have changed over time, but more detailed studies have shown
that their assumptions were wrong. The intensity and concentration of Dark
Energy has remained the same since the Big Bang, it has not changed.
In
discussing the black hole we see that there is an imaginary boundary around the
black hole which depends on the size of the black hole, when an object crosses
that boundary and moves towards the black hole, that object can never free
itself from the very intense gravitational force of the black hole. Even the
light is not released from there. From there no light returns to the outer
world. That imaginary boundary of the black hole is called Event Horizon [Link
to know more about black hole: https://spacejagat.blogspot.com/2021/09/the-black-hole-ocean-of-mystery.html]
There is a similar event horizon in space which is called Cosmic Event Horizon.
From 16 billion or 1,600 light-years away from us, if there is an object, it
would be the most red colour in our eyes due to the maximum range of the Redshift
and then the light of that object would slowly begin to fade after which that
light will be completely disappeared in the darkness of space forever because
the speed of light is only one-fifth of the speed of the expansion of space so
light will never reach our eyes. This imaginary edge of observation in space is
called the Cosmic Event Horizon.
However,
it is true that scientists have not yet been able to reach a unanimous decision
about the Dark Energy, they are a bit confused, and so there are different
models and conclusions to be heard. Some say that in the future this energy
will become so strong that everything in the universe will be completely
shattered. The galaxy, the star, its planets, satellites and even the electrons
and protons inside the atom will be destroyed due to the collapse of the
bonding nature. There will be nothing left to say about structural matter in
the universe, only infinite emptiness. Scientists call this condition the Big
Rip. Another group of scientists thinks that there will come a time when the
dominance of gravitational forces in the universe will continue to increase
again. At that time the speed of space expansion will start to decrease little
by little and there will come a moment when this expansion will stop completely
and space will start shrinking. In the end, the whole universe will come to a
tiny point smaller than an atom, right from where this universe was created by
the big bang, which we know as the Point of Singularity. Scientists have
identified this condition as the Big Crunch. [Links to details about the Big
Crunch are given: https://spacejagat.blogspot.com/2021/10/is-big-crunch-ultimate-consequence-of.html]
Scientists say there will be another Big Bang after that. According to them,
the Big Rip and the Big Crunch occur 1 trillion or 10,000 crore years apart. In
addition to this, there is another group of scientists who say that there is no
such thing as Dark Energy. In fact, all objects in space are moving; they are
spinning on their own axis with great velocity. So the expansion of space is
actually nothing more than an illusion. We have been misinterpreting the whole
thing.
However,
most of the cosmologists have accepted the existence of Dark Energy as accurate
and real, but it is also true that they have not been able to conduct any
research on this subject in laboratory or provide any direct evidence. So even
if there is disagreement on this issue, it is not possible to ignore the
reality of the future. We don't know who is right or wrong, but one thing we do
understand is that something must happen in the future.
DECLARATION: All The Images Have Been Sourced From Google.
