Introduction
This chapter covers the Big Bang theory of the origin of the universe. The theory was proposed by American scientist Edwin Hubble. Today the Big Bang theory is accepted by most astronomers as the best explanation of the origin of the universe.
What is the Big Bang theory?
The term 'universe' means all of time, space, matter and energy. It is everything that we know. The universe holds everything from the tiniest particle to the clusters of galaxies, known as super-clusters.
The Big Bang theory states that the universe was formed about 14 billion years ago as the result of a giant explosion of very dense and hot matter. This matter expanded and started to cool down, going through different transitional phases. The universe has been expanding ever since.
The first scientist to come up with the idea of a 'big bang' was the astrophysicist Friedrich Franz Friedmann who used relativity field equations to prove that the universe is expanding. Edwin Hubble's observations later proved this theory. Hubble discovered the red shift of galaxies. He measured their distances from Earth by observing variable stars called Cepheids. The red shift distance law of galaxies is now referred to as Hubble's Law.
The discovery of cosmic microwave background radiation in 1965 made the Big Bang theory the best theory of the origin and evolution of the universe. Radio astronomers Arno Penzias and Robert Wilson discovered the cosmic microwave (high frequency radio wave) background which is thought to be leftover radiation from the initial explosion of matter - the 'Big Bang'.
Apparently this theory was called 'The big bang' by a radio commentator who was mocking it. Initially the theory was called 'The primeval atom'. Today astrophysicists with a sense of humour sum up the Big Bang theory as the following: First there was nothing, then there was the bang and then there was everything.
The formation of the solar system
According to the Big Bang theory, the solar system was formed from a cloud of space dust and gas that was 'squeezed' by a supernova explosion. As the nebula contracted, it spun increasingly rapidly, leading to frequent collisions between dust grains. Gravity pulled the gas and dust together, forming a solar nebula. This solar nebula grew hotter and denser, forming a disk of gas and dust in its centre. Particles of nebula dust started to stick together, forming clumps that eventually formed planets and their satellites. Eventually the hot centre of the solar nebula formed a star - the sun. Different planetary particles left over from this initial explosion can still be found flying around in space. These particles are called meteorites. By studying these meteorites, scientists have found that our solar system is about 4 600 million years old.
Problems with the Big Bang theory
Like all scientific theories, the Big Bang theory has its pros and cons. For example, the cosmic background radiation, which is the main proof of the Big Bang Theory, comes from widely separated parts of the sky. These regions are too far from each other to be able to interact with each other, even with signals travelling at the speed of light. But according to the smooth background radiation whose sources have similar properties, they must have interacted with each other. This problem is referred to as the 'horizon problem'.
Another problem with the Big Bang theory is the 'flatness' problem. The experimental evidence is that the present universe has very low geometrical curvature in its space-time. In other words, it is flat. According to the Big Bang theory, the universe expands but unless this expansion is confined to an incredibly narrow range of possibilities, it would not have stayed 'flat'.
Scientists and philosophers have been arguing over different theories of the origin of the universe for centuries. All scientific theories are subject to constant re-evaluation and change.
