Origin of Universe; the Big Bang

Timeline of the Big bang; source: wikipedia.org
The universe never fails to surprise us. Every time I look at the night sky I wonder how these marvelous scenes came into existence. When and how it began? How the universe came into existence? Astrophysicists have proposed various theories for the beginning of universe but Big Bang theory is widely accepted among others. We will focus on big bang theory today.

 According to the big bang theory at the beginning (nearly 14 billion years ago) universe was smaller than the smallest atom.

The conditions then can’t be described by the physical laws known to us. The time from t=0 to t=10-43 seconds known as “Planck era”. The temperatures were mind-bogglingly high greater than 1032 K.  During this time gravitational and quantum mechanics are not applied. All the forces we know were united into single unified force. We generally apply quantum laws to molecules, atoms, and subatomic particles; and gravitational laws to celestial bodies. These two theories do not blend together and theory as quantum gravity is not possible yet. In the present universe, this difference doesn’t matter. But during “Planck era” large was small, thus the nature of universe during that time is not explainable yet.

Splitting of unified force into fundamental forces; image source: physics libretext

After the end of the Planck era, it is expected that gravity separated from unified forces. After this time laws of physics known to us are applied.  The two forces then were “gravity” and “electrostrong” interaction. The temperatures dropped here to 1029K. As universe crossed the mark of 10-35 seconds it continued to expand; which lowered temperatures and electrostrong force split into “electroweak” and “strong nuclear forces”. Further as cooling (still 1020K) continued electroweak force split into “electromagnetic” and “weak nuclear” forces.
These distinct forces are ;
·         Weak nuclear forces- they control radioactive decay of atoms.
·         Strong nuclear forces- they bind nucleons within nuclei of atoms.
·         Electromagnetic forces- they bind atoms within molecules.
·          Gravity – it binds bulk matter and governs the movements of celestial bodies.
As 10-12 seconds passed the universe was hot enough that mass and energy were in equilibrium. The energy existed in form of photons and mass in form of matter-antimatter. The photons converted their energy into the matter-antimatter pair. And matter-antimatter destroyed each other forming a photon.  This period is known as “quark-lepton era”. Temperatures here dropped to 1012K. Here universe was the soup of quarks, leptons, antimatter, bosons.

Interconversion of matter and energy; source medium.com

Quarks are charge entities, they have fractional charges (1/3rd). They are inseparable. They are always found in groups. And force binding them increases with separation apply more energy and energy will create another quark. Some evidence suggests that during splitting of the unified force, an asymmetry is created in which particles of matter outnumbered particles of antimatter. Nearly about 1 in a billion matter particle survived in their battle with antimatter. This difference didn’t appear much here but this asymmetry proved essential for the universe’s existence.
After 10-6seconds from the beginning, the universe cooled down to 1010K. And due to expansion density dropped. Now universe was not suitable for new quarks to form. So existing quarks joined together to form hadrons. It soon resulted in the formation of protons and neutrons etc.

Matter and antimatter; image source: indiatoday.in

Slight one in a billion asymmetry in case of hadrons got magnified. On further cooling of universe conversion of energy into matter stopped and photons generated in the matter-antimatter war lost their energy to expansion. A single hadron formed after billion annihilations. These were going to be building blocks of the universe.
Now finally one second from the beginning has passed. The universe is now grown to be few light years in size. But temperature is still 1010 K. At this temperature electrons and positrons were not stable and behaved like matter-antimatter pair, popping in and out of existence.  Thanks to that asymmetry, some electrons survived and settled with protons.
As the universe continued to expand, the temperatures dropped below 108K. Protons fused with protons and neutrons, forming atomic nuclei. These beginners were hydrogen atoms (most abundant element in the universe).
For another 380,000 years, not much will happen in the universe. The densities and temperatures are still hot enough for electrons to roam freely. But as the temperature falls below 3000K and all electrons settle with nuclei. The photons are no longer in thermal equilibrium with matter and universe becomes transparent for the first time. The photons of cosmic microwave background radiation originate here.

Cosmic Background Radiation; source: cosmology.berkely.edu

For billion years universe expanded and cooled as matter started to gather forming chunks of gas clouds and which further concentrated to form galaxies. Hundred billions of them with billions of stars in them. These stars are 10-20 times massive than the Sun. At their core, they can form heavier elements in the last time of their life. And they went supernova to scatter this elemental treasure all across the universe.

Virgo Supercluster, milky way belongs to it. Source: wikidata.org

 After nearly 9 billion years of this sacrificial enrichment. In the outer regions of Virgo supercluster’s milky way galaxy, a star was born in its Orion arm named Sun, our sun. The heavy element-rich gas cloud from which sun was born, concentrated at various rates due to the gravity of the sun and resulted into several rocky as well as gaseous planets. 

The position of the solar system in milky way galaxy; source:  wikipedia.org

Early solar system (artistic imagination); source: phy.org

The solar system was formed and violent pinball continued for several million years until collisions subsided and the solar system got stable.
 Earth being in the habitual zone around Sun (called Goldilocks zone) developed life. And after the evolution of Homo sapiens species and development of technologies, you are here reading an article by the person who came from the same nothingness which you are from.
 And I would close it by a quote by famous astrophysicist Neil de Grasse Tyson 

“The good thing about science is that it’s true whether you believe it or not.”

(I would suggest you astrophysics lover to read his book “Astrophysics for People in a Hurry“.)

Categories: OriginPost


Sandipkumar Sahani · September 19, 2018 at 10:29 pm

You've done a really, really good job..

Ankit Sherke · September 19, 2018 at 10:38 pm

Thank you sir.

Unknown · September 19, 2018 at 11:23 pm

Fab job u have done ankit

Unknown · September 20, 2018 at 3:11 pm

Great work done ankit bro…

Ankit Sherke · September 20, 2018 at 3:23 pm

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