bigbang

Man has always been trying to find the secret behind its existence. Both religion and science ultimately attempt to explain this fundamental question of where we came from. In the very recent past, however we have come closer than ever to discovering the answer to this question. In recent years one theory has been developed that has more physical evidence than any other. This theory is named the Big Bang and has revolutionized the way that we view the cosmos around us.
The history of the Big Bang theory begins when Albert Einstein created his General Theory of Relativity in 1915. Einstein's theory of gravitation of bodies, called general relativity, identified gravity with the curvature of space-time, the four-dimensional plane that consists of the three special dimensions combined with time (Silk, Big Bang 1980 13). In his first cosmological paper in 1917, Einstein attempted to make the equations of relativity fit with the untrue belief that the universe was stable and static, with no creation or end (Monsters 103).
Einstein's theory of relativity received firm verification in 1919, when the deflection of light from distant stars by the sun was calculated during a total eclipse. The cosmological implications of Einstein's theory of relativity began to collect intensive examination. Out of this examination came the idea of the Big bang and an expanding universe, which challenged Einstein's idea of a static and unchanging universe. The theory came chiefly from a Russian meteorologist, Alexander Friedmann, and a Belgian cleric and mathematician, Georges Lemaitre. The formulation of a Big Bang explanation for the universe was extraordinary because both men formulated the hypothesis without any firm observational evidence for universal expansion (Silk, Big Bang 1980 15). Both men, in different years, separately discovered the solutions to Einstein's equations of gravitation, which describe a growing universe. They discarded Einstein’s ideas of cosmology, which he had calculated somewhat as an afterthought, and his perception of a fixed universe. Friedmann, in 1922, and Lemaitre, in 1927, demonstrated that the universe should be in a large-scale expansion. To avoid collapse, the power of the expansion of the universe must balance gravitational pull. The expansion could either continue forever, or eventually reverse into a phase of contraction. A principle realization of their theory was that the matter content of the universe implied that space was not necessarily Euclidean or analogous to the flatness of a plane in a two-dimensional analogy, but could be curved like the plane of a sphere (with a positive curvature) or a hyperboloid (negative curvature) (Silk Cosmic Enigmas 13). Since the surface of a sphere is closed and finite while a hyperboloid is open and infinite, it can be inferred that a universe with high matter density should be closed, finite, positively curved and should eventually collapse, while a universe with low matter density should be open, infinite, and negatively curved, expanding indefinitely.

Next, Edwin Hubble, a renowned American astronomer of the 1920's, revealed a linear relation between distance to a remote galaxy and its red shift in 1929. This provided exciting evidence supporting the idea of the ever-expanding universe from the Friedmann-Lemaitre model. Hubble’s discovery was influenced considerably by the work of a Dutch astronomer, William de Sitter, who in 1917 hypothesized that the universe possessed the odd property that the light from the most distant regions became progressively reddened as the distance increased. Hubble's red shift is due to a Doppler shift of light from a galaxy that is receding. This explains that the distance of galaxies from us is linearly proportional to their red shift and so linearly proportional to their relative speed of recession (Silk, Big Bang 1989 374). So basically, galaxies and bodies that are twice as far from us than another, move twice as fast. This idea indicates that it has taken every galaxy the same amount of time to go from a common point of origin to its current position, wherever that might be.
The Russian born U.S. nuclear physicist George Gamow created the term “Big Bang” for these theories in 1946. He was one of the strongest advocates for this theory for the creation of the universe, supporting the work of Einstein, Friedmann, Lemaitre, and Hubble (Peebles 1). Gamow attempted to explain the distribution of chemical elements throughout the universe through a spontaneous thermonuclear reaction. He also proposed that in the beginning of the Big Bang, the universe consisted of a primordial substance called ylem. This ylem was a gas of neutrons that was at extremely high temperatures exceeding 10 billion degrees. Because the neutrons existed in this "free" state, they began decaying into protons, electrons, and neutrinos. The result was a boiling sea of neutrons and protons that merged together to form heavier and heavier elements. In Gamow's perception, all of the elements in the entire universe formed in this manner during the earliest twenty minutes of the Big Bang. This hypothesis attempted to account for the origin of helium and hydrogen in the universe, and was submitted by Gamow and his partner, Ralph Alpher in 1948(Eldredge 355). Then in a follow up paper, Gamow and Alpher wrote that after the universe was created in a great fiery explosion, as the universe expanded, the radiation would not have persisted but would have been steadily diluted. This would explain the necessary cooling of the universe. But the most important part of this second paper was the prediction of background radiation, a tangible clue to the actual Big Bang. Although in the 1940's there was no technological way to detect such a faint afterglow, scientists of later decades would be able to prove what Gamow had hypothesized.
According to the Big Bang theory, the universe began with one large explosion, which took place about 15 to 20 billion years ago. It is from this theory that we are able to examine the evolution of the universe from the milliseconds of creation to the creation of galaxies, and from the formation of planets to the presence of life on earth. Since almost all astronomical phenomena can be explained entirely within the context of the Big Bang, or if not completely, can be explained to a greater degree than any other mode, this model of the universe has become the most widely accepted up to this point. However, within the framework of the Big Bang theory, there are several different models of the universe.