According to science's most commonly-held theory, a single moment was all that was required for the entire universe to explode into being.
The scenario of how the universe came into being that is currently believed to be most likely is known as the Big Bang Theory. According to this explanation, approximately 13 billion years ago all the matter that is to be found in the universe was squeezed into an unbelievably small spot known as a singularity. Then, when the moment was right, this singularity expanded outwards at an unbelievable speed to create the universe.
The singularity expanded with such force that, just a fraction of a second later, it produced gravity and all the other forces that govern physics. The explosion was so fierce that it generated 10 billion degrees of heat and, in less than three minutes, 98 per cent of all the matter that there will ever be had been produced. We had our universe.
The Big Bang theory was first put forward by Georges Lemaitre, a Belgian priest and scholar, in the 1920s, although the term Big Bang' appeared in 1952 when a Yorkshire man named Fred Hoyle first coined the phrase. However, the theory did not gain much support until the 1960s, when the background radiation left over from the Big Bang was first detected.
It had previously been believed that the Universe was unchanging, but two important discoveries changed this. First, in 1917, Einstein's General Theory of Relativity proved that the universe must be expanding or contracting otherwise gravity would attract all the galaxies to one another. Then, in 1920, Edwin Hubble discovered that the universe was expanding by measuring light from distant galaxies, and this in turn led to Lemaitre postulating his version of the theory, which has become known as the Big Bang model.
The Universe is unimaginably immense and all of mysteries are enfolded within it. But where did it come from and what will eventually happen to it?
Today, the prevailing view among scientists is that you are living in an expanding universe, but what will happen to this expansion is a point of much dispute.
Some believe that gravity may prove to be too strong a force and will eventually stop the outwards movement, so that the universe will one day stop expanding and begin to collapse in upon itself back into another singularity, the Big Crunch, which will then undergo another Big Bang and the process begins over again.
Others believe that gravity may prove too weak a force and so the universe will continue to expand until everything becomes so far apart that the universe becomes inert and dead.
What is agreed by most scientists, however, is that the universe isn't expanding in a traditional sense. That is to say, the universe bends and curves in a way that means it has no center or edge or boundaries. No matter where you were in the universe, everything would be moving away from you because it expands in every direction and dimension at once. This is also the reason why astrophysicists say that there is no such thing as the center of the universe.
Some scientists don't agree with the Big Bang theory and ask how the universe could suddenly have appeared out of nothing. If there was no space, matter, or energy before the Big Bang, then there was nowhere for this singularity to suddenly pop into being and create the universe. Critics also point to a number of other problems with the Big Bang theory.
The universe is not expanding at nearly the rate you would expect had there been a Big Bang. No measurable expansion is observable in our own solar system or galaxy, and Big Bangers simply assume that the expanding of space must be taking place between galaxies where it is safely beyond observational investigation.
Critics also point out that the Big Bang theory predicts that all galaxies formed within a relatively short period, and therefore every one should be around 13 billion years oil, but surveys have found evidence of much younger galaxies.
Furthermore, extremely distant galaxies have been discovered that apparently formed long before the Big Bang universe could have cooled sufficiently and must therefore be older than the Big Bang. Impossible if nothing existed before.
Three arguments support the Big Bang model; firstly, the universe is expanding, so it originated in an explosion. This has been proved by a phenomenon known as red shift'. When light is stretched or moved away from us, its wavelength is longer, causing red light. In the 1920s Hubble observed that all the galaxies, except for a few nearby ones, show red shift.
Secondly, the universe is full of background radiation (the afterglow of the Big Bang) that reaches Earth in the form of microwaves. This was first detected in 1965 using the Bell antenna, in effect, seeing back to moments after the Big Bang.
Thirdly, the Big Bang explains the relative abundances of hydrogen, helium and other light elements in the universe.
A unified theory of the origins of the universe may one day be possible, but until then investigations will continue.