The Big Bang & Universe for Dummies.

Beginning of Everything:

The Universe was just atoms, Just atoms before turning into billions of light years across (which we can only observe). These atoms were the building block of everything known to Existence. These atoms fused together under the Immense heat and pressure from the big-bang forming galaxies, stars, nebulae's, and every single cosmic entity known in the observable universe, Before all these beautiful spiraling galaxies, and stars, There were only random particles (e.g.: photons) scattered around a thick, dense, cloud of plasma which didn't let any radiation pass through, As the universe cooled, Thus protons and electrons now could combine to form neutral "hydrogen" atoms, With the emergence of free electrons now binding to protons, Now the photons could emerge and we could see light travelling through the thick dense plasma cloud, This radiation was the first ever radiation ever traced, and we now know it as the–Cosmic microwave background– The earliest forms of our observable universe when it was in its baby phase.

After Big Bang:

After our universe cooled down and formed basic atoms, It was time for creating all cosmic entities known to existence. As the plasma cooled down it marked the start of a new era–Radiation dominated era– Right after the Big Bang, radiation (light and other forms of energy) dominated the universe. During this time, the energy density of radiation was much higher than that of matter as radiation's density decreases faster than that of matter as the universe expands. Thus our Universe became Radiation Dominated.

As the Universe Further expanded and cooled down, matter started to take over the observable universe and cosmic entities started forming, This marked the end of Radiation Dominated Universe, and Began the Matter dominated era where matter (both dark matter and ordinary matter) eventually became the dominant component because its density fell more slowly than radiation. This era began roughly 50,000 years after the Big Bang & was essential for creation of cosmic structure's. During these eras stars fueled by nuclear fusion were formed, As well as planets formed by materials such as hydrogen & other heavier nuclei , obtained by supernovas and Nuclear fission of dead stars.

Then there comes a time in the history of Space-Time during which we currently live through, A time of Darkness where a mysterious type of matter called "Dark matter" dominate the darkness of Space time, a mysterious form of energy causing the expansion of the universe to accelerate. Dark energy became dominant around 4–5 billion years ago and now accounts for about 70% of the total energy density of the universe, with matter (both ordinary and dark) making up most of the rest. Most of the Stars that are ever going to exist have been formed, and about no new stars will be formed, and once all stars known to existence go supernova, our universe will enter a "Degenerate era", where no stars will exist and blackholes, white-holes, Dwarf Stars, etc., will dominate our universe, the universe will be left with only low-energy particles like photons, neutrinos, and perhaps dark matter particles. The universe will be essentially a vast expanse of nearly nothing—an extremely low-energy, thermodynamically stable, and inactive state. But don't worry as this Era is distant and we may have probably be gone by then. This era will begin after about 10 trillion years from now–So no need to worry!!

Laws formulated by our universe:

Once our universe was made, It formed set of laws which were discovered by great scientists such as Isaac Newton, Einstein, and Edwin Powell Hubble formulated the Principles of our observable universe, Firstly The Uniformity Principle States that the universe is the Same from everywhere, For e.g.: If you stand at 2 points which are at opposite ends of the universe, The universe will be the same at both points. Thus it can be concluded that the universe is uniform, However on smaller scale (100-10k light years) the universe is non-uniform–But how you may ask?–Well the universe is non-uniform on small scales due to gravitational clustering and quantum fluctuations from the early universe. Towards the beginning of our universe inflation took place, Expanding our universe however this took place on macroscopic level resulting in creation of variable densities across the universe, Thus areas with higher densities attracted galaxies and stars further increasing density, Meanwhile for areas of low density, They led to creating of a void further reducing density. All of this led to formation of variable density thus leading in Non-Uniformity on Small Scales.

Then come Hubble Laws which state everything is moving away from us, with speed that is proportional to its Distance. Each atom has tiny quantum fluctuations and oscillates up and down emitting energy, Each atom emits its own radiation, As bodies of matter far away emit these radiations, as the radiation reaches us it stretches, making it larger and that of the Color "Red", Thus calling it "Redshift", Mathematically Redshift is equivalent to Velocity/ Speed of Light, Thus, v = cz. Where c is speed of light and z is redshift, We can rearrange this equation to get Redshift. Hubble also discovered "recession velocity" ∝ "distance" , Thus from this relation we can get: v = H(o) x r, Where "v" is recession velocity, "H(o)" is Hubble's constant, and "r" is distance from earth. You may wonder what is recession velocity? Well recession velocity is the speed at which bodies of matter move away from us, It increases with distance so for e.g.: Object which is 2 million light years away from earth has less recession velocity than an object which is 10 million light years away. Thus Recession Velocity Increases with Distance.

Einstein & his theories of Relativity:

Einstein one of the greatest minds to ever walk the planet, deduced his theories of relativity in which he clearly explains the reasoning behind mind boggling space phenomenon's. Firstly he came up with his theory of Special Relativity in 1905. In his theory he firstly stated the "principle of relativity" which said that laws of physic's remain same around non accelerating frames of time. Then he concluded that the speed of light in a vacuum is 3×10(8) , In this theory he also explained that Time slows down for objects moving at high speeds relative to an observer (e.g., a moving clock appears to tick slower). He also expressed the relation between mass and energy, and deduced that they could be converted to one another, Thus formulating his famous equation: E=mc(2)

Then fast forward a bit in 1915, Einstein proposed his theory of General Relativity which revolutionized physics and made ripples in the community, In his theory he stated that there is no such thing as gravity. Instead he said that matter changes metric of space-time, causing object to fall or curve the fabric of space, and object fall due to natural curvature of space-time, For e.g. in his mind he believed the space-time to be a flat fabric upon which heavy objects with immense mas such as star used to bend the space fabric causing other smaller objects to orbit them. In his eyes' gravity is a fictional force like Centrifugal Force. In his theory the reason we feel gravity pulling us downwards is actually because Ground is pulling us upwards against natural motion (Falling).

Universe and Its Geometry:

The Density means the combined density of everything present in the universe, This Density is represented by 'K', K changes the the geometry(Shape) of the universe. Well there are 3 possible geometries of the universe depending on various densities. In the 1st case/ possibility If a universe has density greater than zero (K >O), The universe was born into existence with Net-negative energy & universe would be a large sphere and a Closed System (like the sun/planets), On this sphere if you travel in any direction you will end up where you started. The universe would be finite & and would have no edges. Parallel would eventually meet at some point and Lastly The angles of a triangle add up to more than 180 degrees. Eventually fate of universe would be "big crunch" and collapse on its own, As the dark energy would not be dominant and the actual density is greater than the critical density, meaning the universe has enough mass to eventually slow down and possibly collapse.

For 2 case/possibility, if a universe has density lower than zero (k<O), The universe was born into existence with Net-positive & the universe would be saddle shaped open system, The universe would be infinite and expand forever. The parallel lines would diverge and move further away from each other. The sum of angles in a triangle would be less than 180 degrees. Eventually as the universe expands forever, accelerating over time, leading to a "Big Freeze" where the universe becomes cold and dark as stars burn out. The big freeze would occur as the actual density is less than the critical density, meaning the gravitational pull is not strong enough to halt expansion.

And Lastly for 3 case/possibility, If a universe has density equivalent to zero (k=O), The universe would be flat like a plane. The universe would be a closed system where the universe would be infinite and unbounded; if you travel in a straight line, you will keep going forever without curving back. Parallel lines would never intersect and remain parallel. The sum of angles in a triangle would be exactly 180 degrees. Further–The universe expands forever but at a slower rate over time, eventually approaching a halt, unless driven by dark energy–As the actual density equals the critical density, so it’s balanced between collapse and indefinite expansion. Our universe that we currently reside is also nearly flat as evidence states, with accelerating expansion driven by dark energy.

Inflation and our Universe:

Now as we discuss inflation, Its crucial to discuss what is inflation in the first place? Well Inflation is the cosmological phenomenon of rapid expansion that occurred right after the big bang. During inflation the universe expands faster than speed of light, The inflation theory helps us explain theories such as Big-Bang, Kepler's and Hubble's law of expansion of universe. Inflation also helps us understand the mystery behind the "Cosmic-Microwave Background". Now lets talk about the logic behind Inflation. Well when the universe was in its early stages, The energy levels were off the Charts, Thus there were millions if not billions of quantum field fluctuations, The fluctuations had an average value of zero, As the universe cooled down and energy value dropped, The field no longer had a value of zero thus required to either go to positive or negative. Thus our universe is at place called "False Vacuum State" where energy levels are at lowest possible, As well as it is at the brink of Decay meaning it could at any time enter "True vacuum state". When the universe is at false vacuum state the Inflation is highest possible during Inflation: Every part of the universe has constant & very large densities, Expansion rates will be greater Thus there will be Exponential Growth, and by the Curvature of space time it will be flattened and there will be the same level of Quantum fluctuation's. Eventually Inflation ends when the universe becomes So large that it enters a true vacuum State, and Growth Ends. This phenomenon can be mathematically shown by the famous Mexican hat.

Conclusion:

In conclusion, from the initial moments of the Big Bang to the intricately woven cosmic tapestry we see today, our understanding of the universe has evolved tremendously. Phases of radiation dominance, matter formation, and dark energy influence pieced together the narrative of cosmic evolution, which enlightens not only our origin but also our expectations for the future. The laws and principles scientists like Hubble and Einstein established our comprehension of cosmic expansion and the basic nature of gravity and spacetime. As we plunge deeper into the mystery of phenomena's such as dark matter and vacuum states, we stand at the cutting edge of a scientific journey promising to reshape our very understanding of existence itself. The exploration of these cosmic principles is not merely an intellectual pursuit but a quest that challenges our understanding of reality and our position in the universe. Much remains unknown in the future, but with every discovery, we get one step closer to unraveling the mysteries of the cosmos, and the journey of inquiry and discovery will live on for generations.