Theory Of An Expanding Universe example essay topic

The "Big Bang" theory of the origin of the universe is a controversial yet widely accepted theory in the creation of the universe to it's present form. Dating back in history, the groundwork of famous scientists and their theories helped to develop the Big Bang theory to what is stands as today. Special note goes to that of Friedmann, Hubble and Einstein who all played major roles in the establishment of this theory and are all included in this essay. Other points that constitute this essay include the origin of the universe, transformation of radiation into matter after the Big Bang and the accretion of stars and galaxies. Aleksandr Friedmann was a Russian professor of mathematics who made an enormous contribution to the development of theories that the universe was expanding.

Living in the time of Albert Einstein's era he took an insight into cosmology. He read Einstein's work with problems associated with relativity's expanding universe. Einstein had proposed that the size of the universe was constant and it neither shrank nor grew. Based on the theory of relativity, Friedmann predicted that the universe must be expanding and argued that space and time have tendencies to be isotropic and that it was possible for the average density and radius of the universe to change over time. He also developed a dynamic equation for the expanding universe in the 1920's. He proved that there were 3 possibilities for the universe when the cosmological constant is zero.

1) If Gravity is stronger than the critical density of the universe, then the universe will ultimately collapse back onto itself. 2) If the inverse is correct the universe would expand forever. 3) If the universe were flat with zero constant then the universe would again expand infinitely. This theory of an expanding universe helped to develop the Big Bang theory. Edwin Hubble, an American lawyer with a PhD in Astronomy began working in an observatory in California in 1919. In doing so, he became the first astronomer to discover an independent galaxy outside of the Milky Way.

The galaxy, named the Andromeda galaxy was calculated by Hubble to be 800,000 light years away. This was further away than any stars known in that time. He used radial velocity measurements with his own measurements to conclude that the further away a galaxy was relative to Earth, the greater the velocity of that galaxy. This was proof that Friedmann's prediction had been correct and that the universe was expanding. There was one major question left unanswered after these discoveries: if the universe is expanding, what was the origination of this expansion? This was where a Belgian Astronomer named Georges Lem a^it re made the statement that the expansion of the universe was an increase in the disorder of a system that had originated from a singularity of neutrons.

This was the beginning of the era towards the Big Bang theory where it was later suggested that all of the matter and energy as we know was initially condensed in a very small and infinitely hot mass that exploded and sent matter and energy expanding in all directions. This explosion, that was trillions of degrees in temperature and infinitely dense created not only matter and energy, but space and time itself. The earliest time in history that anything can be said relating to the universe after the 'Big Bang' is 10-43 seconds. This is done through Quantum Theory and states that at this time the four forces of nature combined to form a 'super force'.

The density at this time is thought to have been 1094/cm^3 with the majority of this being radiation. At this time, the universe was undergoing a rate of expansion many times the speed of light and at 10-35 seconds the isotropic inflation of our universe was almost smooth. At this point, the universe was an ionized plasma where matter and radiation were inseparable and there were equal amounts of particles and antiparticles. During these stages, radiation had to be transformed into matter in order for the universe to be created in the way it did and can be explained below. 'The formation of matter from energy is made possible by photons materializing into baryons and antibaryons with their subsequent annihilation's transforming them into pure energy. ' (Maff ei) At one second after the explosion, the temperature had dropped to ten billion degrees and photons no longer had enough energy to disrupt the creation of matter.

Three minutes later, the universe was a super-hot fog that was still too hot to allow atoms to form. After 300,000 years with a temperature decrease to 10,000^0 C light was finally able to shine and only after 1 billion years from the initial explosion were galaxies able to form due to gravity combining hydrogen and helium gas and making giant clouds. Einstein was the first to theorise that energy could be converted into mass and vice-versa. He showed this through the equation E = mc^2 which can be described through part of a speech he made below: "It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing -- a somewhat unfamiliar conception for the average mind.

Furthermore, the equation E is equal to m c-squared, in which energy is put equal to mass, multiplied by the square of the velocity of light, showed that very small amounts of mass may be converted into a very large amount of energy and vice versa. The mass and energy were in fact equivalent, according to the formula mentioned before. This was demonstrated by Cockcroft and Walton in 1932, experimentally". - Albert Einstein.

With the expansion of the universe being proven, there was yet to be proven how further stars (and galaxies) were formed. It was found that the accretion of stars and galaxies are formed due to massive structures in the centers of galaxies and accretion disks which all relate back to a lumpiness in gas clouds. When galaxies were young, the stars in their cores were very closely packed together which created star collisions and mergers, which in itself created a single massive black hole. An unknown percent of galaxies contain this massive black hole in its core but this is believed to be a major cause of star and galaxy accretion.

Stars and gas are observed to rotate about the centres of galaxies. When the gas gets closer to the massive black hole in the centre of the galaxy, the 'centrifugal force' acting upon the gas will increase where the gas is then expected to settle into a rotating disk known as the accretion disk. Adjacent rings of gas orbiting in the disk will be subject to friction and move towards the black hole. In the outer areas of the accretion disk, the development of gas clouds is present which allows gravitational collapse and further amounts of gas to move toward the black hole. The massive black hole plus accretion disk produces the phenomena seen in active galactic nuclei. Many of these active galactic nuclei produce a pair of jets that carry gas to the outer parts of the galaxy and beyond.

This frictional force is responsible for heating the gas in the disk which can then radiate. Most of this radiant energy will be released fairly close to the black hole and if there is enough gas around the black hole, then the radiation will be re emitted several times before it escapes. Some of this radiation which undergoes the transformation into matter can be intercepted by dust clouds or intercepted by dust grains in the outer parts of the disk which is how stars are accreted inside a galaxy and at a larger scale - how galaxies are accreted. In Conclusion, through the scientific research of Astronomers, Physicists and Cosmologists, this information on the origin of the universe in the form of a "Big Bang" provides essential information as to how the universe was created and how it will continue to exist in the future. With further studies into this theory it is hoped that remaining unanswered questions may be proven with regards to extended space exploration and better understanding of the world we live in.