If we go deep into the universe, the first question comes to our mind is how does this universe form? You will get mostly answer as the model or theory known as Big Bang Theory. So, What is a Big Bang Theory? The cosmologist and scientist use Big Bang Theory as a model to explain the universe formation. It is the idea that the universe began from a single point (small singularity) and then stretched and expanded to grow as it is right now. It describes how the universe expanded initially in a high density and temperature. It gives a broad range of observations to the early stage of the universe.

Who proposed Big Bang Theory?

The starting idea of the big bang theory was proposed by Georges Lemaitre in 1920, and in 1931, appear scientifically in a paper. He is a Belgian cosmologist and a church priest.

Georges Lemaitre
Georges Lemaitre

He was fascinated with Einstein’s law of gravitation published in 1915 and he said that if Einstein’s law of gravitation is true then it meant that the universe must be expanding right now. Later in 1927, Georges published an unnoticed paper in Belgium that provides the compelling solution to the equations of the general relativity for the case of expanding the universe in all directions but it was not static. But there was no proof for it, therefore many scientists ignored it.

In 1929, at Mt. Wilson Observatory, Edwin Hubble using the world’s largest telescope discovered that galaxies are moving away at high speed. With this Hubble and Lemaitre were on the same page. A year later, Lemaitre explained the logical consequences of the expanding universe and boldly proposed that Universe must have originated at a finite point at a time and there was a primordial atom which had contained all the matter of the universe.

Can big bang theory be proven ?

Mainly where do we get the clue of the big bang that happened 14 billion years ago? From the speeding galaxies proportional to the distance to ancient gas clouds that can be detected today. This story gives the origin of the universe.

Almost all galaxies are moving away from our Milkyway galaxy with some at 100 to 1000 kilometers per second. If most galaxies moving away from us that meant the universe is expanding. And if the universe is expanding then it must have started from a smaller point. This shows that all the matters in the universe were packed on a small point and started expanding outward. The expansion of the universe from a small point (primordial atom) can be called a big bang theory.

expansion of universe
expansion of universe

We can understand how the galaxies are moving away from us by the concept of sound and light. So, when we hear sound from a nearby object then we hear a high-pitch voice. Similarly, when we hear the same sound from far away than we hear a low-pitch voice. Here, the sound gets stretched and low-pitch from far away.

Similarly, the light also has the property of waves. When the speed moving objects like galaxies moving way than light which is detected are getting stretched. That makes the light seems redder. The faster-moving galaxy, the redder the light is more.

Another thing can be capturing the afterglow light of the big bang. Humans can see the visible ray of light only. There are other kinds of light that exist in the universe but we cannot see it with our naked eyes such as X-ray, u-v ray, microwaves, radio waves, etc.

As the universe started expanding the light gets stretched into microwaves. A detect microwave we need a microwave telescope to see the ancient lights from the early universe. When we look to the sky with a microwave telescope we get to see a glow, day, and night, and the glow is known as Cosmic Microwave Background.

What did happen after the big bang?

The Big Bang Model is typically broken down into few key eras and events.

eras and events of big bang
eras and events of big bang

Scientists pick the story up about 10 to the minus 36 second that is one-trillionth of a one trillionth of a one trillionth of a second – after the big bang. we think the big bang is an explosion of matters but the big bang is not an explosion of matters moving upward to fill an empty universe. Instead, space itself expands time everywhere and increases the physical distance between call moving points.

For brief moment, after big bang by most common model of big bang Is that the universe was filled homogeneously and isotropically hey very high energy density and huge temperature and pressure and was very rapidly expanding and cooling.

The first period of expansion was from 0 to 10^-43 second and the Planck epoch phase has begun in which four fundamental forces were unified that is the electromagnetic force, strong nuclear force, weak nuclear force, and gravitational force. In this stage, the universe pure form of energy, and it was very hot for the creation of any particle.

At 10^-37 of expansion, there was a cosmic inflammation due to phase transition, during which the universe grew exponentially unconstrained to the speed of light invariance, and the temperature also drops by the factor of 100,000. At this point, due to Heisenberg’s uncertainty principle, there is an occurrence of Microscopic quantum fluctuation.

Now the inflammation stopped around 10^-33 to 10^-32 seconds where the universe volume has been increased by the factor of at least 10^78. At this point, the universe has acquired the temperature where the production of a quark-gluon plasma as well as all other elementary particles can be held. But the temperature was so high that the motion of the particle was at relativistic speed and particle, anti-particles pairs were continuously created and destroyed in the collision. At some point, there was a violation of baryon number by the reaction of baryogenesis which leads to excess amount quark and lepton over antiquark and antilepton. This results in the predominance of matter over anti-matter.

The universe density and temperature started falling down gradually. Due to which the typical energy of each particle decreases. At about 10^-6 quark and gluons combine to form baryons such as protons and neutrons. As the temperature falls by therefore now there were no creation protons and neutrons, so a mass annihilation occurs immediately. Similarly happened, at 1 second with electrons and positrons. After the annihilation, electrons, protons, and neutrons do not move relativistically and the universe energy density was dominated by protons.

As the universe cooled, rest energy density came to gravitationally dominant that of photon radiation. And after 379,000 years, the electrons, protons, and neutrons combined to form atoms and were able to emit radiations.

Over a long period of time, highly denser regions of the uniformly distributed matters were attracted by gravitational force by other matters and thus became immense denser than before and started forming clouds, stars, galaxies, etc.

How can be a Big bang theory be disapproved?

Actually a scientific theories are never disproved but they are replaced by better theories as an development as time passesby.

Similarly Big bang theory can be replaced by some other new theories when the theory explains currents observations that is explained by big bang theory and also even more further and accurate explanations.

Some of the points that can be explained by new theories can be on:

  • Cosmic expansion is seen by isotropic redshifting of galaxies on large scales.
  • The uniformity and isotropy of the cosmic microwave background.
  • The cosmic abundance of light elements(H and He).
  • The finite age and lifetime of all-stars we have ever observed.
  • The origin of the observed large scale filamentary cosmic structures called the cosmic web.

and much more.

Recently, research published in 2019, shocked the world by maintaining that the theory may be disapproved with age estimation of the “Methuselah star“.

Methuselah star- the oldest star of the universe
Methuselah star

HD 140283 also known as Methuselah star has been observed for 100 years. It is found that this star is the oldest star of the universe found in the Libra constellation and 190 light-years beginning of the 20th century. Methuselah star moves across the sky at the speed of 1.3million kilometers per hour.

The astronomers estimate that the age of Methuselah star is 14.5 billion years old, and plus or minus 800 million years. This has shocked the scientific community as the age of the universe, determined by the observation made through cosmic microwave background is estimated to be 13.8 billion years. Here comes the question that, how a star can be much older than this universe according to big bang model analysis?

Methuselah star is now bloating into a red giant and was probably born on a dwarf galaxy that nascent milky way gloped up more than 12billion years ago. However, further studies are conducted for evidence of the theory of the big bang.

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