THE BIG BANG THEORY


INTRODUCTION
How did our universe come to be? Many believe that our universe an infinite horizon, yet this immensity was born from an infinitesimal spec. One of the most widely accepted theories is the Big Bang Theory. At one point in time, our universe was the center of a black hole, a nearly indescribable place with indescribable characteristics, as we have yet to discover the full truth on black holes. At the core of this black hole existed a “singularity,” yet another “impossible” occurrence in the world of science. This is a point when all matter is infinitely hot, infinitely dense, and unmeasureably small. At one point, however, this area expanded and cooled at once, incredibly creating the Earth and the universe around us. Truly amazing is the fact that our world was sent to a place with such specific characteristics, such a perfect distance from the sun, and with such necessities, that we can carry on life amongst the many living creatures on the face of our planet.

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The Theory In A Nutshell

The standard model of the Big Bang theory proposes that the universe emerged from a singularity, at time zero, and describes all that has happened since 0.0001 of a second after this moment of creation. The temperature of the universe at that time was 1,000 billion degrees Kelvin and had a density that of nuclear matter, 1014 grams per cubic centimeter (the density of water is 1 gram per cubic centimeter). Under these extreme conditions, the photons of the 'background' radiation carry so much energy that they are interchangeable with particles. Photons create pairs of particles and antiparticles which annihilate one another to make energetic photons in a constant interchange of energy in line with Einstein's equation E = mc2. Because of a small asymmetry in the way the fundamental interactions work, slightly more particles were produced than antiparticles - about one in a billion more particles than antiparticles.

When the universe had cooled to the point that photons no longer had the energy required to make particles, all the paired particles and antiparticles annihilated, and the one in a billion particles left over settled down to become stable matter.One-hundredth of a second after time zero the temperature had fallen 90% to 100 billion K. By one-tenth of a second after time zero the temperature was down to 30 billion K. The temperature after 13.8 seconds was down to 3 billion K, and by three minutes and two seconds had cooled to 1 billion K, only 70 times hotter than the centre of the Sun today. At this temperature nuclei of deuterium and helium could be formed and stick together despite collisions with other particles.During the fourth minute after time zero reactions took place that locked up the remaining neutrons in helium nuclei, as described by Gammow et al in 1940 and Fred Hoyle and others in the 1960's. This epoch ended with just under 25% of the nuclear material converted into helium, and the rest left behind as lone protons - hydrogen nuclei.

By just over 30 minutes after time zero, all of the positrons had annihilated with almost all of the electrons - with again one in a billion left over - to produce the background radiation proper, and the temperature had dropped to 300 million K, and the density was only 10% of that of water. At this temperature stable atoms were still not able to form.The interactions between electrons and photons continued for 300,000 years, until the universe had cooled to 6000 K, roughly the temperature of the surface of the Sun, and the photons were becoming too weak to knock electrons off atoms.Over the next 500,000 years the background radiation decoupled, and had no more significant interaction with matter. The Big Bang was in effect over, and the universe left to expand and cool. About 1 million years after time zero, stars and galaxies could begin to form. Nucleosynthesis inside stars convert hydrogen and helium to make heavier elements, eventually giving rise to our Sun, the Earth and ourselves.


"The evolution of the world can be compared to a display of fireworks that has just ended; some few red wisps, ashes and smoke. Standing on a cooled cinder, we see the slow fading of the suns, and we try to recall the vanishing brilliance of the origin of the worlds." Lemaitre

An overwhelming weight of evidence has convinced cosmologists that the universe came into existence at a definite moment in time, some 13 billion years ago, in the form of a superhot, super dense fireball of energetic radiation. This is known as the Big Bang theory. Until the arrival of the Big Bang theory the universe was believed to be essentially infinite and unchanging, represented by the Steady State model. The first clear hint that the universe might change as time passes came in 1917 when Albert Einstein developed his General Theory of Relativity. Einstein realized that his equations said that the universe must be either expanding or contracting, but it could not be standing still, because if it were then gravity would attract all the galaxies towards one another. This was, at the time, a revolutionary concept, so revolutionary that Einstein refused to believe it and introduced his infamous 'cosmological constant' into the equations so that the sums agreed that the universe could be static. It was in 1920 that Edwin Hubble discovered that the universe was expanding by measuring the light from distant galaxies. This discovery was followed in 1927 by Georges Lemaitre, a Belgian astronomer, who was the first person to produce a version of what is now known as the Big Bang model.
It is necessary to understand that the Big Bang did not begin as a huge explosion within the universe, the Big Bang created the universe. A popular misconception is that it happened within the universe and that it is expanding through it. This causes people to wonder where in the universe it started, as if by running the clock backwards we would reach the point where all the galaxies come together in the center of the universe. The universe does not have a center, any more than the surface of a sphere has a center, there is no preferred place that could be pin pointed the center. I know this sounds weird; it must have a center, mustn't it? The problem we have here is we are trying to visualize the universe in the standard 3 dimensions that we are familiar with and therefore expect to find a center to an expanding sphere. The universe, however, is not an expanding 3 dimensional sphere, it contains also the dimension of time and many other dimensions as well. By way of an illustration imagine a balloon with dots painted on the surface to represent the galaxies. If the balloon is inflated we can see that all the dots are moving away from one another, just as the galaxies are in the real universe, and we can also see that on the surface of the balloon there is no center point from which all the galaxies are moving away from. I am not suggesting that we exist on the 'outside' of an expanding bubble, only that we cannot visualize the entire expanding universe.

Just After the Big Bang
The Planck Epoch and the Grand Unification Epoch
The time from 10-43 to 10 -35 seconds after the big bang is known as Planck and Grand Unification epochs. Today, we know very little about this period of time because our current physics theories cannot explore time depths any deeper than this. Although little is known, we do know that the four fundamental forces known today were unified as one super-force. Those forces are strong nuclear, weak nuclear, electromagnetism, and gravity. Currently this is just in theory, but scientists today are working to find a physical theory to explain this epoch. As a result of the Planck Epoch, gravity separated itself from the super-force, creating the force of gravity and the “electronuclear” force. At the beginning of the Grand Unification Epoch, the universe was smaller than a quark. As the universe expanded and cooled, and the electronuclear force broke apart into the strong nuclear force, the weak nuclear force, and electromagnetism. By the end of this epoch, the universe was the size of a proton.
The Inflationary Epoch
During the Inflationary Epoch, which lasted about 10-32 seconds, the universe grew at a rate of 1026, resulting in the universe growing to the size of a grapefruit. During this stage, the volume increase by 1078. Post inflationary epoch, the universe continued to expand to its current size today, which is 92 billion light years in size.

The First Elements
It was not until about three minutes into the creation of the universe that protons and neutrons reacted and formed deuterium. Deuterium, which is an isotope of hydrogen, then collected another neutron and formed tritium. Immediately after this reaction, it gained a proton, which then created a helium nucleus. Scientists believe the ratio of helium nuclei to protons was 1:10 during this time period. Once the universe cooled, the excess protons, with the addition of an electron, were able to form hydrogen. This is still observed in the universe today because it is known that for one helium atom, there are ten of eleven atoms of hydrogen.


EXPANSION OF THE UNIVERSE
In the 1920's, an American astronomer by the name of Edwin Hubble was extremely interested into the future of the universe. His studies proved to him, and the rest of the science world, that the universe is constantly expanding, which goes in accordance with the Big Bang Theory. So how did Hubble discover this incredible piece of astronomical information??? Using high-powered telescopes, light emitted from galaxies far away can be seen, and the color of this light tells a very interesting story, as Hubble discovered. In the spectrum of light, red is at an extreme, as it contains the longest wavelenghts of the spectrum. This being said, if the light seen through the telescope was red, then the galaxies far away were moving further away. Hubble discovered, in depth, that this light could be referred to as "redshift," and that the galaxies around Earth are moving away from our Solar System, and that the ones farther away are moving at an even faster pace. This information is vital when the future of the universe is studied, as it is a very popular topic at this moment in history.

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This diagram, from NASA, shows the possible expansion, and possible contractions, of our universe. As it can be seen, we are currently at the point when all four of these possibilities meet. The orange line represents a universe that is extremely dense, and contracts just as fast as it expanded, in a parabolic graph. The green graph shows a universe that is critically dense, and slowly decreases its expansion, with time becoming more and more horizontal, and constant in its expansion. The blue graph represents a universe that is slowly contracting, but slower than the previous two due to a lack of gravitational pull that would further affect the growth and expansion of the universe. The final, red, graph shows a universe with a large amount of "dark energy". This energy causes the expansion of the universe to accelerate, which is why the graph becomes more and more vertical with an increase in billions of years. This curve is the most widely accepted to be the type of universe that we live in. This would indicate that our universe still has a lot of years to live.
Citations

"Big Bang Theory." All About Science. N.p., 2010. Web. 26 Mar 2010. <http://www.big-bang-theory.com/>.
"Foundations of Big Bang Cosmology." National Aeronautics and Space Administration. N.p., n.d. Web. 31 Mar 2010. <http://map.gsfc.nasa.gov/universe/bb_concepts.html>.
"THE BIG BANG." University of Michigan. N.p., 2009. Web. 31 Mar 2010. http://www.umich.edu/~gs265/bigbang.htm.