The Big Bang
Many astronomers are convinced that between 12 billion and 20 billion years ago the universe came into existence with the dramatic ‘big bang’. In the 1920s, the American astronomer; Edwin Hubble discovered that the universe was expanding when he measured the distances of clusters of galaxies from one another. Albert Einstein also predicted expansion by his general theory of relativity. If the universe is moving apart, it can be said that in the past all matter and space was once concentrated closely together.
The standard theory of the origin of the universe started from a point called time zero whereby happened a process of inflation; all of the mass and matter of the universe that was compressed to a size smaller than a proton suddenly emerged from a singularity and rapidly started expanding for billions and billions of years, into the universe that we know today. Within 15x10-33 seconds of the inflation initiating, the universe doubled 100 times or more from a size 1020 times smaller than a proton, to about 10cm. Due to the exceedingly dramatic and violent nature of this inflation, the universe is still expanding to this day and will do so for a very long time.
The temperature of the universe when it was ten thousandths of a second old was about a thousand billion degrees oc, cooling down to about 100 billion degrees oc a hundredths of a second after the start of the expansion. By this time the number of neutrons and protons changed from being equal, to about 24 neutrons for every 76 protons; one second after the beginning point when the temperature cooled to 10 billion degrees oc and the universe had a density ‘only’ 300 000 times that of water.
By about 14 seconds the universe had cooled to only 3 billion degrees oc and the conditions were gentle enough to allow the processes of nuclear fusion to operate (this is the process that can be found inside an atom bomb and in the centre of the sun). Three minutes after the beginning, the universe cooled to 1 billion degrees (70 times hotter than the centre of the sun) with 14 neutrons for every 86 protons and that the deuterium nuclei (a heavy form of hydrogen) could form and survive despite being bombarded by a constant stream of other particles and radiation. 30 minutes after the beginning, the universe cooled to 300 million degrees oc and had a density 10 times that of water. The hydrogen and helium that was being formed interacted with radiation to form what is known as plasma; similar to the state of matter found inside the sun today.
This activity continued for 300 000 years as the universe cooled to 6000oc (the same as the surface of the sun) which whereby allowed the hydrogen and helium to start procuring electrons and so to form atoms. It was not until a million years after the beginning that stars and galaxies could start to form; the rest is history.
The future of the universe is unsure, but one possible ending might be the reverse of the Big Bang – the Big Crunch, where gravity pulls all of galaxies and stars back together again; for a repeat of the big bang.