Harrow and Hillingdon Geological Society
Big Bang
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The big bang and the expanding universe.
Graham Marrett
This presentation explained the development of ideas about the origin of the universe and how the large majority of professional cosmologists and astronomers now believe that:
• The universe began with a big bang 13.7 billion years ago.
• In the first 10-35 seconds the universe inflated by a factor of 1050 to about 10m in diameter.
• The first atoms formed after about 300,000 years.
• The first galaxies formed about 5 billion years later.
Ancient times
Aristotle in 350BC said that at the instant of creation, the prime mover (or creator) set the heavens in perfect and eternal motion, circular or spherical in nature and centred on the earth; further, he believed that all matter was composed of the 4 elements – earth, air, fire and water. Adjusted a little by Ptolemy, this view lasted about 2,000 years and it was adopted and adapted by Christian theology.
16th century
In 1583, Nicolas Copernicus published his The revolution of the celestial sphere, which recognised that the planets of the solar system revolved around the sun. This view was rejected by the church and Galileo suffered persecution as a result of his adopting it. Copernicus did not change the concept of divine and instantaneous creation. The mechanics were later explained by Johannes Keppler and by Isaac Newton and his Law of universal gravitation.
20th century
Developments in the early 20th century included Albert Einstein revolutionising the understanding of space and time through his Theory of relativity and later Quantum theory explained the world of energy and particles at atomic and sub-atomic scales.
Since the 1970s, scientists have been trying to combine understanding of the macro-scale of relativity and the micro-scale of quantum theory. Theorists began to probe the earliest time. 10-42 seconds was explored mathematically. According to relativity, this event created time and space and the universe expanded. It did not expand into pre-existing space but space itself expanded.
Big Bang theory
The theoretical basis of the Big bang theory owes its origin to the Belgian Georges Lemaitre (1894-1966). The experimental evidence supporting the big bang is based largely on the discovery of background radiation by Penzias and Wilson (1961).
A key understanding is needed of why matter clumps together as it does eg in the solar system, which is part of a galaxy (the Milky Way), itself part of a local group of galaxies (including Andromeda), which is part of the Virgo super-cluster, itself part of a large-scale structure. Also needed is an understanding of why the sub-atomic world of particles and forces (such as the newly discovered Higgs boson) is so complex when the primordial universe is believed to be relatively simple.
There is also a religious dimension. In 1951, Pope Pius XII said that scientists are beginning to find the finger of God in the creation of the universe. The Church had recognised its faults in the persecution of Galileo and, in 1981, it held a conference on cosmology at the Vatican. This was attended by Stephen Hawking, who, in an audience with the Pope, was told that it was legitimate to study events after the big bang but the event itself was the work of God and physicists should not go beyond. Stephen Hawking said that there was no moment of creation because time did not exist; it only came into existence at the big bang.
Gravity is the key to the large-scale structure and behaviour of the universe. All remember Galileo’s experiments to show that different masses fell at the same speed (if air resistance is discounted). Keppler built on the observations of Tycho Brahe to formulate the Laws of elliptical orbit then Newton developed his Law of gravitation. This led naturally to the consideration of an infinite universe.
If the universe is infinite, it leads to serious problems. Richard Bentley challenged Newton on certain aspects of an infinite universe, claiming serious problems with stability. Ultimate collapse under gravitation is only avoidable if matter was uniformly distributed in space. He speculated that this exquisite balance could only be maintained by divine power. The stability of matter in the universe remains a major problem.
In an infinite universe with an infinite number of structures radiating energy, we would be overwhelmed by radiation (Keppler). This question also puzzled Heinrich Olbers (1788-1840) and became known as Olbers paradox. It was suggested that this would not arise because the universe has radiating stars and vast dust clouds, which absorb the radiation. However, in an infinite universe with an infinite amount of radiation, the dust clouds would be heated to such an extent that they would start to radiate in their own right.
The first possible explanation came from Edgar Alla Poe, who suggested that the night sky was dark and we were not overwhelmed by radiation because the light from distant stars had not yet reached us.
Einstein
In 1905, Einstein published his Special theory of relativity with its explanation of the strange relationships between space and time and between mass and energy. This said that light should travel at the same speed for all observers (ie the speed of light is constant) and put forward his famous equation e = mc2. More correctly it should be called a restricted theory of relativity, since it applies only to objects travelling at uniform speed and not to those accelerating or under gravity.
In 1915, he published his General theory of relativity in which the strange space-time continuum and the mass-energy relationship were linked through the curvature of space-time by mass-energy. This was verified by observational experiment of the total eclipse of the sun in 1919, which showed that light from distant stars was curved around the sun. This theory predicted that the universe was expanding rather than static and Einstein introduced his cosmological constant to avoid expansion. When Hubble revealed in 1927 that the universe was indeed expanding, Einstein withdrew his cosmological constant as his “greatest blunder”.
The first solution of Einstein’s equations was by Carl Schwartzchild (1966) for a single mass in an otherwise empty universe. This predicted bending of light by the sun, as had been seen in 1919 and also predicted the existence of black holes.
What do we mean by empty space?
Newton’s concept of absolute time was supported by Immanuel Kant and others. The alternative view was that the reality of space was only supported by the view of what it contained. Mach’s principle of motion and inertia in space is defined by the totality of mass in the universe. De Sitter predicted expansion of the universe with no matter and, in 1922, Friedmann also predicted an expanding universe with significant amounts of matter.
Until the early 1920s, it was not generally known that distant galaxies existed. Edwin Hubble (1889-1953) studied what were the known as spiral nebulae using the Mount Wilson telescope in California and Henrietta Leavitt discovered a technique for measuring distances based on Cepheid variable stars. Hubble measured the Andromeda galaxy at 800,000 light years away and concluded that the spiral nebulae were distant galaxies. Andromeda appears to be moving towards us, while others are moving away (Andromeda’s light is shifted to the blue end of the spectrum while others show a red shift). The farthest away are receding fastest indicating that the universe is expanding.
Fred Hoyle
In 1931, Lemaitre propsed the big bang theory in that he suggested the universe started as a primordial atom. This was not universally accepted. Fred Hoyle (1905-2001) accepted an expanding universe but not a big bang. He proposed his Steady-state theory, in which new matter is slowly being created as the universe expands. This did not require a big bang and, indeed, Hoyle coined the term Big bang as a derogatory term for a theory he thought was wrong.
There are 4 key issues:
• Age of the universe – the big bang predicted 2 billion years, when geological evidence already showed the earth to be older than that. In the 1950s, it was found that Hubble had under-estimated the distance to galaxies and the new age was 10-20 billion years.
• Abundance of elements – the big bang was not able to explain the origin of the heavier elements; Hoyle suggested that supernova explosions explained this.
• Distribution of galaxies – density should increase back with time
• Temperature – there should be over-riding temperature due to the big bang itself.
Hoyle in 1955 considered that there were no obvious relics of a super-dense state of the universe to be found. However, new surveys confirmed that density does increase with distance and Hoyle conceded in 1965 that steady-state may have to be discarded as it was unsupported by evidence.
Arnold Penzias and Robert Wilson in 1964 investigated noise interference with the Echo communications satellite, which was originally attributed to a white dielectric material in the horn. After the horn was cleaned, the noise persisted. They had discovered the 3.5oK background radiation which permeates the universe, the afterglow of the big bang itself. There should be very minor variations in radiation in different areas of the sky and in 1989, the Cosmic background explorer (COBE) satellite was launched to look for these tiny variations (1 in 100.000) in temperature of the background radiation. The COBE map (1992) shows these variations. The later W map confirmed this distribution. The figure of 13.7 billion years for the age of the universe comes from analysis of the COBA and W maps.
Conclusion
The study of microwave background radiation will form the heart of cosmological research in the 21st century.