The Big Bang Theory

The Big Bang Theory is one of the best approaches that explain the birth of the universe. It is a widely accepted model as it conceives the scientific origin of the universe.


The origin of the universe remains a mystery. For instance, several cultures have advanced myths explaining the origin of the universe during early civilization. According to the Chinese myth, for example, the universe originated when a ‘great creator hatched from an egg’. The universe as we know was borne from the giant’s body when it died. As people began to study the universe applying the tools of science, they searched for explanations that matched their observations very closely.

The branch of science that devotes itself to the study of the origin and structure of the universe is known as cosmology. Thus, cosmologists are scientists who specialize in the field of cosmology. These scientists have developed detailed ideas that describe the origin and evolution of the universe. These ideas are commonly referred to as theories. The Big Bang Theory is one of the best approaches that explain the birth of the universe. It is a widely accepted model as it conceives the scientific origin of the universe.

The word ‘big bang’ was coined by Fred Hoyle to describe cosmology in which the universe expanded into being from a dense state to a finite time in the past (Barrow, 235). The Big Bang theory postulates that the universe began in a single instant, in an imaginable powerful explosion. All elements of time and space, matter, and energy were created by this powerful and imaginable explosion. Since that explosion, the universe has been expanding for about 14 billion years.

What remains from one fiery moment of creation is the universe we see. This idea is known as the Big Bang theory, one of the most significant theories in modern science. This theory offers the best explanation we have about the origin of the universe. It is not perfect nor is it complete, and does not offer answers to every question about the origin of the universe (Barrow, 234). The Big Bang theory is sufficiently supported by measurable observations which strongly support the argument that the cosmos evolved from a dense, nearly featureless hot gas. These measurable observations are the expansion of the universe; cosmic background radiation; and the light elements (Barrow, 238).

Relativity Theory

The Expansion of the Universe

The Big Bang theory came out as a natural outcome of Albert Einstein’s general relativity as used to a homogeneous universe (Davis, 72). The theory offers a mathematical description of the cosmos. Relativity model as advocated by Einstein, governs the science of the universe. This theory addresses the overall structure of the universe. Einstein’s general relativity equations can be applied to show that a finite universe must have a larger density of matter and energy in it, than an infinite universe would have. The universe began from a sort of powerful explosion, beginning from infinite density and temperature.

The Big Bang explosion occurred everywhere. All particles in the universe have been moving away from one another since the Big Bang. They were carried along by the expansion of space that is, all sufficiently distant particles have been moving away from one another since the Big Bang. Particles highly clustered and close together are affected by their mutual attractive forces and do not participate in the overall expansion of the universe. For instance, the atoms in your body are held in place by an electrical force and do not expand away from one another. Likewise, the stars in the galaxy are held in place by the mutual gravitational attraction and do not expand away from each other (Davis, 72).

Although the universe expands, its parts cling together due to attraction by gravity. The element of competition that exists between the outward motion of expansion and the inward pull of gravity leads to three possibilities for the fate of the universe: first, the universe may expand forever, with its outward motion always overwhelming the inward pull of gravity (Barrow, 243). For example, a rock thrown upward with sufficient speed will escape the gravity of the earth and keep traveling forever.

This type of universe is called an open universe; second, the possibility that the inward force of gravity is sufficiently strong to halt and reverse the expansion, just as a rock thrown up with insufficient speed will reach a maximum height, and then fall back to earth. This type of a universe is referred to as a closed universe. This universe reaches a maximum size and then starts collapsing, towards a kind of reverse bang. These types of universes have both a beginning and end in time; third and final possibility is referred to as a flat universe and is analogous to the rock thrown upward with precisely the minimum speed required to escape from the pull of the earth.

Just like open universes, flat universes keep expanding forever (Koupelis et al, 568). The Big Bang theory allows all these three possibilities. The type of the universe that holds in on our universe depends upon the manner in which the cosmic expansion started; in the same way that path of the rock depends on the rock’s initial speed relative to the strength of the earth’s gravity. The critical initial speed for the rock is 7 miles per second.

If a rock is thrown upward with less than this speed, it will fall back to earth; rocks with greater initial speed will never return. The fate of the universe likewise, was determined by its initial rate of expansion relative to its gravity. The fate of the universe can be inferred by comparing the current rate of expansion to its current average density (Barrow, 165). If the density is less than the critical value determined by the current rate of expansion, then gravity dominates; the universe is closed, faced to collapse at some time in the future. If the density is less than the critical value, the universe is open. The universe is flat if it is equal to the critical value. Thus, the universe is flat, open, or closed depending on whether omega is less than 1, or larger than 1 respectively (Barrow, 242).

In 1917, scientists continued to cast doubt on the concept of the earth’s expansion. This scenario led to Einstein to invent the cosmological constant. He applied this in the general relativity theory. This theory gave an allowance for a static universe. In 1929, Edwin Hubble made a great discovery in his observations that the universe of the galaxies is not in static position but it is in a state of constant expansion (Longair, 10). The basis of Hubble’s discovery was the observation that all galaxies were receding from our own galaxy, and that the further away a galaxy is from us, the greater the velocity, expressed as Hubble’s law;


V represents the recessional velocity of the galaxy; r is the distance of the galaxy and H* is a constant, commonly known as ‘Hubble’s constant’ (Longair, 11).

Cosmic Background Radiation

Cosmic background radiation is an important observation that supports the Big Bang theory. It is commonly referred in a long winded name of ‘Cosmic Blackbody Microwave Radiation’. It’s cosmic because it comes from all directions, blackbody because of it has spectrum shape, and microwave because its spectrum speaks at centimeter to millimeter wavelengths. The Cosmic Background Radiation is a major piece of observation initially regarded as unwanted noise in radio receiver that was being developed for commercial use by scientists at Bell Laboratories (Davies, 4).

The discovery of this radiation attests to Big Bang theory of the universe as follows: first, radiation enables scientists to see the raw, young universe. It can then be concluded that the universe was indeed quite homogenous and isotropic (Barrow, 261); second, the present temperature of about 2.7 Kelvin and the isotropy of the radiation allow us to lay out the thermal history of the universe, that is, the change of temperature of matter and radiation with time; third, the presence of radiation establishes an important marker for the formation of the galaxy, until after the ionized gas had recombined, cooled matter formed clumps that eventually formed stars and galaxies; fourth, the radiation provides a reference for measuring the motion of the galaxy and the local group. In the direction of any such motion, the cosmic radiation is blue shifted and so appears to be hotter in that location in the sky, the radiation is red shifted and so appears to be cooler (Barrow, 235).

The Light Elements

This evidence described nucleosynthesis in the early universe. The formation of heavier elements such as atomic nuclei with many protons and neutrons from the lighter elements is referred to as nucleosynthesis. High temperatures were observed to have existed in the early universe according to the Big Bang theory. It is estimated that temperature in the early universe was approximately 10 billion degrees immediately after the big bang.

The space in this early universe was filled with many neutrons, electrons, protons, and others. Cosmologists observed that as the universe cooled after expansion, neutrons decayed into protons and electrons. It is also possible that these neutrons combined to form deuterium (Zuckerman et al, 8). The Big Bang theory is taken seriously because it accounts for the observed light elements. This means that the nuclear processes took place during the first ten minutes of cosmic expansion.

Problems associated with the Big Bang Theory

Flatness Problem

According to the Big Bang theory, the universe can have one of the basic geometries. These geometries can be open or closed in terms of general relativity. The one applicable to the cosmos can be evaluated by examining the ratio of the measured density that is of matter and energy, to the critical density predicted by Einstein’s general relativity and the values of Hubble’s constant (Davis, 64). A universe whose actual density is exactly the critical density is flat has the ratio of 1. Now if at the big bang the ratio were 1, it would remain 1 forever. However, if the value differed from 1 ever so slightly, the ratio would be much different from 1 now.

Surprisingly, the ratio is believed to have a value of between 0.1 and 2, very close to 1. It must have begun very close to one; otherwise, as the universe evolved, the ratio would have acquired a value much different from 1. The Big Bang theory has a special beginning condition that is; the geometry of the universe had to be very close to being flat. However, it does not provide an explanation for this (Davis, 54).

Horizon Problem

The cosmic background radiation uniformity informs us that the universe was extremely isotropic at the time of decoupling. The background radiation deviates from complete uniformity by only a few parts in a million. It doesn’t explain how this happened (Davies, 35). The standard big Bang theory only assumes that it began in that manner and stayed in that manner, and with this assumption, the uniformity of cosmic background radiation poses a problem.

For instance, consider a gas in a box. If you add energy to one side of the container, the temperature rises up. To deduce this effect, the particles in the gas must carry information about addition of the energy by moving around at a greater average speed and knocking into each other faster. A finite time must elapse before these collisions can carry throughout the box the information that the energy has been added to it. Now imagine the box expanding much faster than the particles in it, on the average, they were moving around. Then only a small region of the box would find out that energy had been added, and this part would have a temperature different from the rest (Barrow, 72).

Information can not be communicated faster than the speed of light, yet the very early universe expanded so fast that regions of it were rapidly and widely separated. Now in a given time, a light signal can travel some maximum distance called horizon distance (Davis, 35). For instance, after one second had eclipsed, light could have gone only one second of light travel time for a horizon distance of a bout 300,000 km. As a result of rapid expansion, however, parts of the universe were separated by almost a hundred times this distance. Horizon problem is realized since it does not offer an explanation on how this region evolved at the same temperature when they could not communicate to each other (Davis, 36).

Inflation Theory and the Solutions

Inflationary theory was invented to integrate particle physics with cosmology which had a new success with variation of the Big Bang theory (Davis, 4). The inflationary model copes with the flaws manifested in the Big Bang model and improves them. The model enumerated on a number ways of coping with problems associated with the Big Bang theory as follows: first, it neatly and naturally solves the flatness problem seen in the Big Bang Model. Space and time consisted of strongly curved regions before inflation. Automatically, inflation would cause these curved regions to achieve flatness.

For instance, consider the curved surface of a partially inflated balloon. Blow up the balloon rapidly, keeping a close eye on the curvature of the surface. It will be observed that the balloon becomes less flat. Similarly, when the universe is inflated, the curved regions would become flat. In this case, the ratio of the actual to the critical density naturally reached a value very close to 1, without the need of a special assumption (Davis, 59); second, the horizon problem exhibited in the Big Bang model is solved by inflation theory by altering the setting of the rapid expansion of the universe. The universe is said to have evolved from a region much smaller than in the standard Big Bang model.

It was much smaller than its horizon distance before the inflationary era begun. Therefore, the whole universe could reach the same temperature. Then inflation made it much larger preserving the uniformity of the temperature. This accounts for the great uniformity of the cosmic background radiation in the past and today; third, magnetic monopole problem is resolved by the cosmic inflation which removes all point defects from the observable universe in the same way that it drives the geometries of flatness (Davis, 48).

Other Theories explaining Origin of Universe

There are other theories that explain the origin of the universe besides the Big Bang theory and inflationary theory namely: one, the Bouncing Universe Theory developed by a physicist called John Wheeler. According to Wheeler the universe came into being with a big bang. The universe expanded for a while and the then imploded at a certain point in time. In this model, the universe is thought to follow a cylindrical pattern of expansion and contraction; two, the Protouniverse Theory which explains the formation of matter from nothingness before the explosion of the big bang.

This theory was formed with the aim of explaining the non-uniformity and the varying density of the universe; three, the Bubble Universe Theory which explains the creation of the universe from the quantum foam of a ‘parent universe’; four, the Steady State Model, which observes that the universe does not evolve and will not change in time, that is, it is static. According to this theory, the universe has no beginning and is not expected to change in the future. This model is a perfect cosmological principle, that is, a model that sees the universe to be the same at all times. It also assumes that matter is maintained at all times.

Big bang

  • Expansion of molecular material – to form subatomic particles and basic forms
  • Stars were formed by nuclear fusion – energy and matter fuse
  • Gravity – force of two masses pulling towards each other
  • Life cycle of stars – moves around gaining new forms
  • New elements – formed by reaction, heat and pressure exerted on stars to consume hydrogen

The solar system

  • The sun- condensation of a large collection of matter to explosion in nuclear fusion
  • Planets – combination of new elements together to form the solar system
  • Earth – melting and subsequent transformation resulting in different layers of earth.
  • Biosphere – fusion of elements and later evolution to bring about oxygen.
  • Pangea – The earth was a large mass which later drifted to form continents


  • Elements to beings – Chemical compounds resulted in microbial and complex forms
  • Variations of living things – adaptations, procreation, self-stabilization and energy intake
  • Species and their origins – various forms organisms after transformation from elements
  • Extinctions – dire conditions and events wiping out certain species for birth of new forms
  • Development of DNA – chemical composition necessary for reproduction of species
  • Growth and life on earth-organisms that bred species and the various life forms

Humans and Human evolution

  • Using tools, shelter and fire – evolution of man from initial basic life forms
  • Gathering, hunting and migration-advancement of forms of life and cultures
  • Development of writing and knowledge – the need to communicate and pass knowledge
  • Agriculture – with increase in population came the need to provide food and specialize
  • Civilization – Cities and states sprout up and Cultural interaction ensued

Current living and the future

  • Modern era – the current times interaction and revolution
  • Sources of energy and Population – the need for energy to power machines for growing population
  • Climate, atmosphere and environments – the effects of industrialization and growing population
  • Business, energy sources and globalization – with growth in infrastructure paved way for interactions
  • Inventions – innovations to safeguard and provide efficient livelihood
  • Generations – changing times, growth, and prevalence of human beings over the earth
  • The future – growth in intelligence, inventions and what the current practices portends.