The Big Bang Theory
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The big bang theory proposed that the the universe started with a big explosion, which happened 15 billion years ago.. It states that before the 'big bang', there were no space or time and only energy existed. These energy were concentrated into single point called 'singularity'. Before one second had even passed after the explosion, the space was quickly expanding to the size of a pea then to the size of the solar system and the temperature was about 100 million trillion trillion degrees Celsius. Matter, in the form of tiny particles, protons and neutrons had also been formed and the particles collided which resulted in the release of a huge amount of energy in the form of light. This caused the universe to become very bright. At this point in time, atoms still didn't existed. One second after the 'big bang', the universe had expanded to more than trillion trillion kilometers across and the temperature has cooled to about 10 billion degrees Celsius. Five minutes after the explosion, the nuclei of hydrogen, helium and lithium had formed.
Three hundred thousand years after the 'big bang', the universe had expanded to one thousandth of its present size, the temperature had cooled to about 3 000 degrees celsius and the first atoms were formed. Two hundred million years later, the first stars appeared and nuclear reactions took place inside these stars. The reactions formed swirling clouds of matter which cooled and formed into 'clumps'. These 'clumps' were the beginning of the planets. One billion years later, the universe had became a bit 'lumpy' and the first galaxies were formed.
Three hundred thousand years after the 'big bang', the universe had expanded to one thousandth of its present size, the temperature had cooled to about 3 000 degrees celsius and the first atoms were formed. Two hundred million years later, the first stars appeared and nuclear reactions took place inside these stars. The reactions formed swirling clouds of matter which cooled and formed into 'clumps'. These 'clumps' were the beginning of the planets. One billion years later, the universe had became a bit 'lumpy' and the first galaxies were formed.
The Steady State Theory
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The steady state theory was proposed in 1948. This theory rejected the big bang theory and gave another explanation on the creation of the universe. The theory states that there was no beginning, or end, to the universe, it was always there. It proposed that the galaxies are continually moving away from each other and in the extra space between the galaxies, new stars and galaxies were created. These new stars and galaxies replaced those that move away, hence, the universe always looks the same.
The Great Debate
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After the proposal of the two different theories, a great debate between scientists arose to decided which was the right theory. This debate raged from 1948 to 1965. During this time period, the evidence supporting the big bang theory grew which resulted in the big bang theory winning the debate.
Evidence Supporting the Big Bang Theory
The redshift, subtle changes in the color of starlight, is used to find planets, measure the speeds of galaxies and track the expansion of the universe. The redshift supported the big bang theory and questioned the steady state theory. It shows that there is no way to explain how new stars or galaxies can form for nothing. In addition to that, the proposed young stars and galaxies have never been found by astronomers.
The amount of hydrogen and helium present in the universe also supported the big bang theory. It is believed that 8.7% of atoms in the universe are helium, quite a large amount. The steady state theory stated that helium were only produced in nuclear reactions taking place in stars, however, the amount of helium that is present is far more than what could be produced by stars alone. These amount, however, can be explained by the big explosion in the big bang theory.
The amount of hydrogen and helium present in the universe also supported the big bang theory. It is believed that 8.7% of atoms in the universe are helium, quite a large amount. The steady state theory stated that helium were only produced in nuclear reactions taking place in stars, however, the amount of helium that is present is far more than what could be produced by stars alone. These amount, however, can be explained by the big explosion in the big bang theory.
The People Involved
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Edwin Hubble, born on the 20th of November 1889, discovered that the universe was expanding. His observations and discovery triggered the two major theories, the big bang theory and the steady state theory.
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Georges Lemaitre was a Catholic Priest from Belgium. In 1927, he made a theory, the big bang theory, to explain the creation of the universe.
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Albert Einstein, one of the greatest scientist of all time, attended one of Georges Lemaitre's lecture and agreed with his theories. His famous equation 'E=mc2', where e stands for energy, m for mass and c for speed of light, backed up the big bang theory by proposing that energy can be changed into matter.
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In 1948, Fred Hoyle, along with Hermann Bondi and Thomas Gold, proposed the steady state theory. Although the big bang theory won the great debate, Fred Hoyle's theory was still able to answer one of the most difficult question in cosmology, how the heavier elements came into being.