What is it?

1. It is a theory that the universe as we know it began 10 – 15 billion years ago.

2. Initial state was a hot, dense uniform soup of particles that filled space uniformly, and was expanding     rapidly.

One of the most persistently asked questions has been 'How was the universe created?' In the past many individuals believed that the universe had no beginning or end and was truly infinite. By introducing the Big Bang theory however no longer could the universe be considered infinite. As a consequence the universe was forced to take on the properties of a finite phenomenon, possessing a history and a beginning...

Scientists estimate that about fifteen million years ago a tremendous explosion started the expansion of the universe, an explosion known as the 'Big Bang.' At the point of this event all of the matter and energy of space was contained at one spot. hat existed prior to this event is something not yet known and at this point in time is down to pure speculation. This occurrence was not a conventional explosion, but rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. What we must realise at this point is that the Big Bang was rather an explosion within itself, rather than say an explosion of a bomb, where fragments are thrown outwards. The galaxies were not all clumped together, the Big Bang simply lay the foundations for the universe.

So where can the origins of the Big Bang theory be traced to? Many papers credit this to one Edwin Hubble, who made the observation that the universe was a body that was continuously expanding. He discovered that a galaxies velocity is proportional to its distance. Galaxies that are twice as far from us move twice as fast. Another finding was that the universe is expanding in every direction. This observation means that it has taken every galaxy the same amount of time to move from a common starting position to its current position.

Since the Big Bang the universe has been continuously expanding and thus there have been more and more distance between clusters and galaxies. This phenomenon of galaxies moving further away from each other is known as the red shift. As light from distant galaxies approach earth there is an increase in space between earth and the galaxy., which leaves to wavelengths being stretched.

In addition to the understanding of the velocities of galaxies emanating from a single point there is further evidence for the Big Bang. In 1964 two astronomers, Penzias and Wislon, in an attempt to detect microwaves from space, inadvertently discovered a noise of extraterrestrial origin. The noise however did not seem to emanate from one source, but instead came from all directions! It became apparent to them that what they were hearing was in fact radiation from the fairest reaches of the universe, which had been left over from the big bang. The discovery of this radioactive aftermath of the initial explosion gives much credence to the Big Bang theory.

A more recent discovery by Nasa's COBE satellite was able to detect cosmic microwaves emanating from the outer reaches of the universe. These microwaves were remarkably uniform, illustrating the homogeneity of the early stages of the universe. However the satellite further discovered that the universe began to cool and was still expanding, and as a result small fluctuations began to exist due to temperature differences. These fluctuations verified prior calculations of the possible cooling and development of the universe just fractions of a second after its creation. These fluctuations in the universe provided a more detailed description of the first moments after the Big Bang. They also helped to tell the story of the formation of galaxies which we will discuss later.

What happened next?

Thus far we have grappled wit the theory of the Big Bang...and so the next logical step is to ask what happened next. Immediately after the Big Bang the universe would have been tremendously hot as a result of both particles of matter and anti matter rushing apart in all directions. As it began to cool, at around 10"-43 seconds after creation , there existed almost an equal yet asymmetrical amount of matter and anti matter. As these two materials are created together they collide and destroy one another creating pure energy. However perhaps more fortunately for our own existence there was an asymmetry in favour of matter. As the direct result of the excess of about one part per billion, the universe was able to mature in a way favourable for matter to persist. As the universe first began to expand, this discrepancy grew larger. The particles which began to dominate were those of matter. They were created and that decayed without the accompaniment of an equal creation or decay of an anti particle.

As the universe expanded further, and so cooled, common particles began to form. such particles are known as baryons, and contain photons, neutrinos, electrons and quarks, which would become the building blocks of matter and life as we know it. During the baryon genesis period there were no recognizable heavy particles such as protons and neutrons because of the still intense heat.

After the universe had cooled to about 3000 billion degrees Kelvin a radical transition began which has been likened to the phase transition of water to ice. Composite particles such as protons and neutrons became the common state of matter after this transition. Still complex matter could not form at these temperatures.

After one to three minutes since the creation of the universe protons and neutrons began to react with each other to form deuterium, an isotope of hydrogen. Deuterium, or heavy hydrogen, soon collected another neutron to form tritium. Rapidly following this reaction was the addition of another proton which formed a helium nucleus. scientists believe that there was one helium nucleus for every ten protons within the first three minutes of the universe. After further cooling these excess protons would be able to capture an electron to create common hydrogen. Consequently, the universe today is observed to contain one helium atom for every ten or eleven atoms of hydrogen.

The existence of the universe

Thus far we have began to answer two key questions...what was the big bang and what happened directly after it. The third question would need to address the age of the universe today...Science has been able to expand upon this question by applying the common physical equation of distance over velocity equaling time, which again uses Hubble's observations - by which an approximation can be made.

The two primary measurements needed are the distance of a galaxy moving away from us and the galaxies red shift. An unsuccessful first attempt was made to find these distances through trigonometry. Scientists were able to calculate the diameter of the earths orbit around the sun, which was augmented through the calculation of the suns motion through our own galaxy. However this calculation could not be used alone to determine the enormous distance between our galaxy and those which would enable us to estimate the age of the universe because of the significant errors involved.

The next step was an understanding of the pulsation of stars. It had been observed that stars of the same luminosity blinked at the same rate, much how a lighthouse would work when rotating say every 30 seconds. with such knowledge scientists assumed that stars in our galaxy that blinked at the same rate as stars in distant galaxies must have the same intensity. Using trig they were able to calculate the distance to the star in our galaxy. Therefore the distance of the distant star could be calculated by studying the difference in their intensity much like determining the distance of two cars in the night. Assuming the two cars lights had the same intensity it would be possible to infer that the car whose headlights appear dimmer was further away from the observer than the other car whose headlights would seem brighter. However this theory could not be used as a standalone measurement, afterall after a certain distance it would become impossible to distinguish individual stars from the galaxies in which they exist. Because of the large red shifts in these galaxies a further method had to be devised to find distance using entire galaxy clusters rather than stars alone.

By studying the sizes of galaxy clusters that are near to us, scientists can gain an idea of what the sizes of other clusters might be. As a consequence a prediction can be made about their distance from the milky way much in the same way that the distance of stars was learned. Through a calculation involving the supposed distance of the far off cluster and its red shift, a final estimation can be made as to how long the galaxy has been moving away from us. In turn this number can be used inversely to turn back the clock when the two galaxies were in the same place at the same time, or the moment of the Big Bang. The equation which shows the age of the universe is as follows.....

                                   (Distance of a particular galaxy) / (That galaxies velocity) = Time

When figures are applied to this equation (which we will not go into) the answer comes out to be around fifteen billion years. This calculation is almost exactly the same for every galaxy that can be studied, and therefore when using this evidence that is what we estimate the age of the universe to be.

And so....

In summarising what we have thus far we seem to have made an attempt to explain the answers surrounding the universe. Our understanding of the Big Bang, the first atoms and the age of the universe is obviously incomplete. As time wears on more discoveries are made, leading to more questions which will need answering.

Since its conception the theory of the Big Bang has been constantly challenged. These challenges have led those who believe in the theory to search for more concrete evidence which would prove them correct. For example in June 1995 astronomers were able to confirm one of the requirements for the foundation of the universe through the Big Bang.....the detection of primordial helium, such as deuterium, in the far reaches of the universe. These findings are consistent with an important aspect of the Big Bang theory that a mixture of hydrogen and helium was created at the beginning of the universe.

In addition the Hubble telescope has provided certain clues as to what elements were present following creation. Astronomers using Hubble have found the element boron in extremely ancient stars. They postulate that its presence could be either a remnant of energetic events at the birth of galaxies or it could indicate that boron is even older, dating back to the Big Bang itself. Again if the latter is true then scientists will have to review their theory of the Big Bang, as at present such a heavy and complex atom could not have existed. These are just a few examples that support the theory of the Big Bang...so what do its critics state when arguing against it.......

What is describes

1. How the early universe expanded and cooled

2. How the light elements formed

3. How the matter congealed to form stars, galaxies, and clusters of galaxies

What it doesn't describe

1. What caused the expansion

2. Where did the matter come from