05. Speaking Section:
06. Writing Section:
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Listening Test 1.9

Professor – The Big Bang theory is the prevailing cosmological model that explains the early development of the universe. According to the Big Bang theory, the universe was once in an extremely hot and dense state, which expanded rapidly. This rapid expansion caused the universe to cool and resulted in its present continuously expanding state. The most recent measurements and observations are in agreement with a Big Bang that would have occurred approximately 13.75 billion years ago, which is thus considered the age of the universe. The Big Bang is a well-developed scientific theory, which is widely accepted within the scientific community because it offers an accurate and comprehensive explanation for a broad range of phenomena that astronomers observe. Since its conception, abundant evidence has arisen to further develop and strengthen the model. George Lemaître first proposed what would have become the Big Bang theory in what he called his hypothesis of the primeval atom. Over time, scientists would build on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein’s general relativity and on simplifying assumptions such as homogeneity and isotropy of space. Using the Big Bang model, it is possible to calculate the concentration of helium 4, helium 3, deuterium, and lithium 7 in the universe. All the abundances depend on a single parameter, the ratio of photons to baryons. Measurements of primordial abundances for all four isotopes are consistent with a unique value of that parameter. This refers to Big Bang nucleosynthesis. Steady state theories fail to account for the abundance of deuterium in the cosmos because deuterium easily undergoes nuclear fusion in stars and there are no known astrophysical processes other than the Big Bang itself that can produce it in large quantities. Hence, the fact that deuterium is not a rare component of the universe suggests that the universe has a finite age. Furthermore, one piece of evidence for the Big Bang model is that it resolves Olbers’ Paradox. Olbers’ Paradox is the question of why the sky is black at night. One weakness of the Big Bang theory is the obvious question of how the Big Bang occurred. The difficulty of answering this question lies with the absence of a theory of quantum gravity. As one goes back in time, the temperature and the pressures increase to the point where the physical laws governing the behavior of matter are unknown. It is hoped that as we understand these laws that we will better be able to answer the question of what happened before the Big Bang. Strangely enough, when the Big Bang theory was originally proposed, it was rejected by most scientists and enthusiastically embraced by the Pope because it seemed to point to a creation event. Well, most scientists nowadays view the Big Bang theory as the best explanation of the available evidence and the Catholic Church still accepts it. Some conservative Christians, usually fundamentalists, oppose it because they see a contradiction between the theory and a literal interpretation of the creation stories from the Bible. Progress towards reconciliation between science and this religious interpretation has been made by a physicist whose name is Gerald Schroeder, who claims that his calculations confirm the relativistic correspondence between the measured age of the universe and the six days of creation described in the book of Genesis from the Bible.