The Big Bang theory

Formulated through a concerted series of researches extending way back to the early 20th century and continuing to this day, the Big Bang theory is an informed answer to the question of how the universe originated.

The phrase – Big Bang– was itself coined in 1949 on a BBC radio talk show by British Astronomer Fred Hoyle. While it did come under significant opposition in its early days, modern times have provided a much more holistic bank of evidence to support its claims.

Getting to grip with the basics

At a fundamental level, the Big Bang theory states that the known universe developed as an expansion of a singularity. This expansion resulted in the spontaneous growth of the universe, eventually culminating in the formation of all known matter.

In its early stages, matter in the universe existed primarily as atoms derived from subatomic particles. Over time these atoms would go on to fuse and form an initial assembly of stars and galaxies, the primordia of the visible universe as we know it today.

Also formed in the embryonic stage of the Big Bang was dark matter, a non-visible but nonetheless observable part of the universe. The exact nature of dark matter is still a subject of scientific research; however, a growing body of evidence suggests that it might as well form the major bulk of the universes’ mass.

The foundations of the Big Bang theory

Underlying the Big Bang theory and providing a starting point to develop on its many notions/propositions are two fundamental assumptions; the cosmological principle and the belief that all physical laws are essentially universal.

The cosmological principle puts it that the universe is generally isotropic and homogenous on a large scale; the principle of universally applicable physical laws, on the other hand, assumes that physical laws are as applicable on earth as they are in other parts of the universe.

  • Time-lapse of the Big Bang:

From its onset (or creation), the universe can be said to have gone through a sequence of distinguishable phases. Each phase represents a transition to a notably distinct characterization, different from the preceding stage and leading into the next phase. As of today, the universe is currently experiencing a cosmic acceleration and is said to be in the cosmic phase, but it all started with the singularity.

  • The singularity phase:

If a cosmic path is retraced from the expansion period in the chronology of the universes’ development, it leads to a specific point in time on that roadmap characterized by the presence of an entity with infinite temperature and density. The presence of such an entity or, more precisely, a singularity with limitless density and temperature is a pointer to the fact that the general theory of relativity was well obsolete beyond this point on the timescale – such an entity cannot exist within our current definitions of the laws of physics. Conversely, the presence of this singularity marks the point on this cosmic timescale where the universe verifiably enters into a phase where the laws of physics, specifically the standard models of particle physics and general relativity, become applicable.

It is the ‘palpable’ starting point of the universe and using measurements from several indicators including temperature changes originating from the cosmic microwave background, the formation of this singularity is said to have happened approximately 13.8 billion years ago.

  • The expansion phase:

After its formation, the singularity spontaneously proceeds into a phase of rapid expansion. Several explanations have been put forward to describe this phase; however, the recurring theme is that the universe as it were was composed of an isotropic and homogenous high energy density, towering towards extreme pressures and temperatures while the universe was itself expanding.

The products of this amalgam of high-density energy, pressure, and temperature were both an exponential growth in the ramifications of the universe and formation of the building blocks of its final form. Elementary particles were derived after expansion stopped, and heating continued. Simultaneously, baryogenesis an unknown reaction occurred, leading to an excess of leptons and quarks over antileptons and antiquarks. This effectively set the precedence for an abundance of matter ahead of antimatter in the known universe.

  • Cooling into structural entities:

As the temperature of the universe dropped, so also did its density and general energy levels. Importantly, this phase presented optimum conditions for the creation of subatomic particles, catalyzing reactions that led to the formation of baryons from gluons and quarks. Once the temperature dropped to a level insufficient to support the creation of these proton-antiproton pairs, a mass extinction event occurred, leaving behind just 1010 of all the original baryons.

It took another 379,000 years for electrons, protons, and neutrons to combine and form atoms, mostly in the form of hydrogen. The origin of life, however, started at a much later date, possibly 10-17 million years after the universe was formed.

  • Creation of structural entities:

Over time denser areas of the formed universe attracted slightly less dense bodies and, in so doing, grew to form the majority of the observable structures in the universe. That includes galaxies, stars, gas clouds, and all known components of the universe.

  • Cosmic acceleration:

More recently, it has been discovered that the universe was slowly expanding with time. The nature of this expansion is, however, unique in that the velocity of a galaxy receding from an observer’s viewpoint appears to be increasing with time. In other words, the rate of expansion was increasing with time and approaching the speed of light. The driving force for this accelerated expansion is conventionally thought to be dark energy, and like the baryon reaction, its exact nature is still unknown.

Empirical evidence

Aside from the mathematical framework provided by Albert Einstein’s general theory of relativity, several observable occurrences lay further credence to the validity of the Big Bang theory. The most notable of which include:

  • The expansion of the universe in accordance with Hubble’s law
  • The cosmic background radiation – a product of the electromagnetic radiation derived as an offshoot of the Big Bang
  • The abundance of prehistoric elements
  • The distribution and evolution of known galaxies – which follow the general morphology and distribution of galaxies expected in a universe created from the Big Bang

How it should all end

In time, the universe would compress on itself transitioning back into the highly dense and hot entity it once was; or in another scenario, it would cease expanding with stars slowly burning out and the universe itself reaching a stage where its temperature draws nearer to absolute zero. These were the propositions of cosmologist with regards to the fate of the universe before the advent of dark energy (which seemingly propels cosmic acceleration).

So, what is the fate of the universe in the context of the cosmic acceleration? Current experimental models suggest that much of the existing and visible universe will simply expand beyond our observable horizon, i.e., even though events may occur in these sections of the universe, we might be unable to observe them or their effects. While all this is at this point merely postulations, there is no arguing the fact that the universe is constantly changing, and some would say evolving. The product of that evolution would be the next cosmic phase, and if science fails to give a definitive prediction, time, as always, will provide the final answer.

Article author: write_artist (Fiverr.com)

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