The Origins of Our Universe
In The Beginning...
Evidence For The Theory
Limitations Of The Big Bang Model
The Big Bang Theory is the dominant scientific theory about the origin of the universe. The theory suggests the universe was created
approximately 14 billion years ago due to a single cosmic explosion. It was observed that the galaxies were all moving apart from one another,
hence they, at one point in the past, must have all originated from the same place. The big bang theory was suggested as an explanation for this.
Although the Big Bang Theory is widely accepted, it probably will never be proved, and consequentially this will leave a number of unanswered questions.
In The Beginning...
It is a widespread misconception that the big bang model suggests that the universe began from a single point, underwent an explosion,
and the universe has been flying apart from this single point. However, the big bang was not what we consider to be a conventional explosion.
Instead, the model is of the expansion of space. the 'explosion' is one filling space with all of the particles, rushing away from one another.
What existed prior to this event is completely unknown, and at present is a matter of pure speculation.
The big bang did not occur at any point in time or space. The big bang created time and space. The singularity did not appear in time or space, but everything,
space, time, energy and matter, began inside the singularity. Particles of matter and antimatter
began rushing apart from one another, creating time and space as they moved through the vacuum where nothing existed before. The early universe
was extremely hot. As the opposing matter was created together, they collide and annihilate one another, creating vast amounts of energy. Fortunately for us,
there was in imbalance in the favour of matter, and the universe was able to expand in such a way that matter was able to persist and dominate. It was not until
the universe began to cool that the matter which was created began to form common matter particles we find today such as photons, neutrinos, electrons and
quarks. During this period no heavy particles, such as protons or neutrons, formed due to the intense heat.
After the universe had cooled to around 3000 billion degrees Kelvin, Hadrons became the common state of matter. Lighter particles, leptons, also existed,
but these individual particles were unable to react in order to form more complex states of matter such as elements. After about two minutes since the creation of
the universe, the particles began to combine, forming the elements hydrogen and helium.
It must be taken into consideration that much of this information is speculative, but as the universe ages we are able to better understand and become
increasingly confident in its past. These ideas and theories have arose due to study of the universe the way it is today, studying the formation of
simple atoms in the laboratory, and making educated guesses based on the observed evidence.
Evidence For The Theory
In 1929, Edwin Hubble Observed that the universe is continuously expanding, and that the velocity at which a galaxy is moving away from us is proportional
to the distance it is from us. This results in the conclusion that the universe is expanding in every direction, meaning that it has taken the same amount
of time for every galaxy to move from a common starting point to itís current position. Hubble's observations provided the basis for the foundation of the
Big Bang theory.
- We are reasonably certain the universe had a beginning.
- Galaxies are moving away from us at speeds proportional to their distance.
- If the universe was initially very hot, we should be able to find some remnant of this heat.
- The abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.
It can be seen that the galaxies are moving away from one another by the phenomenon known as red shift. The increasing distance between a galaxy and
Earth results in the wavelength of electromagnetic radiation emitted from the galaxy being stretched as we view it. The stretching of wavelengths causes a
shift towards the red end of the spectrum, hence the term 'red shift'.
In 1964, two astronomers, Arno Penzias and Robert Wilson, were attempting to detect microwaves from outer space. Inadvertently, they discovered a
background noise which came from all directions. What they had discovered was in fact electromagnetic radiation that was remnant from the Big Bang.
This important discovery gave further credibility to the Big Bang theory.
Even more recently, NASAs COBE satellite was able to detect cosmic microwaves emanating from the outer reaches of the universe. These microwaves were
remarkably uniform, which illustrated the homogeneity of the early stages of the universe. However, the satellite also discovered that as the universe cooled
and expanded, small fluctuations began to exist due to temperature differences. These fluctuations confirmed calculations of the possible cooling and
development of the universe just fractions of a second after its creation, providing a more detailed description of the first moments after the Big Bang.
The observed abundances of the light elements in the universe also support the big bang theory, as they are found in relative abundances approximately
equal to those predicted by the theory.
Limitations Of The Big Bang Model
The Big Bang model, with no amendments, would tend to produce a universe that is highly inhomogeneous, with a warped and curved space, and no
natural mechanism for making stars, galaxies and larger scale structures in the universe. Cosmologists have been attempting to correct these deficiencies by
looking at and amending the early history of the universe, periods within the first billionth billionth billionths or less of the universe's creation.
Although the big bang model successfully explains the cosmic microwave background spectrum and the origin of light elements,
it fails to give an answer to a number of important questions, such as why the universe is so uniform on the largest length scales,
why the physical scale of the universe is so much larger than the Planck scale (the fundamental scale of gravity), why the universe
contains so many photons, and what physical processes produced the initial fluctuations in matter density.
The Inflation Theory offers answers to these questions, as well as several other questions in cosmology. It proposes a period of extremely rapid
exponential expansion of the universe leading to the Big Bang expansion, during which time the energy density of the universe was dominated by a
cosmological constant term, that later decayed to produce the matter and radiation that fill the universe today.
The Ekpyrotic model is a new alternative, and a more radical departure from the Big Bang concept. It is not a completely
new idea altogether. Instead the model amends the earliest moments of the big bang theory. The rest of the story follows the current model.
Instead of beginning with extremely high temperature and density, nearly infinite, the Ekpyrotic model suggests an opposite beginning state,
where the universe began cold and nearly vacuous. The hot expanding universe resulted from a collision that rose the temperature and density of the
universe up to a large, but finite, value.
The Ekpyrotic model is based upon the idea that our hot big bang universe was created from the collision of two three-dimensional worlds moving inside
a hidden extra dimension. The two worlds collide and combine, and the kinetic energy of the collision is converted into matter which is confined to three
dimensions. the resulting temperature is finite, hence the hot big bang phse begins in the absence of a singularity. The universe is homogeneous, as the
collision and initiation of the big bang phase occurs almost simultaneously everywhere. The energetically preferred geometry for the two worlds is flat,
leading to the collision producing a flat big bang universe.
Quantum effects cause the incoming three-dimensional world to ripple along the extra dimension prior to collision, so in some places, the collision
occurs at slightly different times. By the time the collision is complete, the rippling leads to small variations in temperature, which lead to temperature
fluctuations in the microwave background and the formation of galaxies.
The building blocks of the ekpyrotic theory are derived from superstring theory, which requires extra dimensions for mathematical consistency.
(Note:Inflationary theory is based on quantum field theory, a well-established theoretical framework, and the model has been carefully studied and vetted
for twenty years. The Ekpyrotic theory proposal is brand new, based on unproven ideas in string theory.)
Whilst the Big Bang theory is well established and widely accapted, it is being, and will continue to be, constantly researched, updated and
refined. There are many areas the current theory has difficulty explaining and providing answers for, but new ideas and theories are being found and tested.
We are currently a long way off discovering a universal theory which explains everything, and we may never have a complete answer as each new idea or
discovery produces more problems and questions. However, with current workin cosmic string theory, particle physics, and the fields of dark matter and dark energy,
hopefully, someday, we may have an answer.