BIG BANG THEORY

"The evolution of the world can be compared to a display of fireworks that has just ended; some few red wisps, ashes and smoke. Standing on a cooled cinder, we see the slow fading of the suns, and we try to recall the vanishing brilliance of the origin of the worlds." Lemaitre

An overwhelming weight of evidence has convinced cosmologists that the universe came into existence at a definite moment in time, some 13 billion years ago, in the form of a superhot, super dense fireball of energetic radiation. This is known as the Big Bang theory. Until the arrival of the Big Bang theory the universe was believed to be essentially eternal and unchanging, represented by the Steady State model. The first clear hint that the universe might change as time passes came in 1917 when Albert Einstein developed his General Theory of Relativity. Einstein realised that his equations said that the universe must be either expanding or contracting, but it could not be standing still, because if it were then gravity would attract all the galaxies towards one another. This was, at the time, a revolutionary concept, so revolutionary that Einstein refused to believe it and introduced his infamous 'cosmological constant' into the equations so that the sums agreed that the universe could be static. He later claimed it was the biggest blunder of his career. It was in 1920 that Edwin Hubble discovered that the universe was expanding by measuring the light from distant galaxies. This discovery was followed in 1927 by Georges Lemaitre, a Belgian astronomer, who was the first person to produce a version of what is now known as the Big Bang model.

It is necessary to understand that the Big Bang did not begin as a huge explosion within the universe, the Big Bang created the universe. A popular misconception is that it happened within the universe and that it is expanding through it. This causes people to wonder where in the universe it started, as if by running the clock backwards we would reach the point where all the galaxies come together in the centre of the universe. The universe does not have a centre, any more than the surface of a sphere has a centre, and there is no preferred place that could be termed the centre. I know this sounds odd, it must have a centre, mustn't it? The problem we have here is we are trying to visualise the universe in the standard 3 dimensions that we are familiar with and therefore expect to find a centre to an expanding sphere. The universe, however, is not an expanding 3 dimensional sphere; it contains also the dimension of time and many other dimensions as well. By way of an illustration imagine a balloon with dots painted on the surface to represent the galaxies. If the balloon is now inflated we can see that all the dots are moving away from one another, just as the galaxies are in the real universe, and we can also see that on the surface of the balloon there is no centre point from which all the galaxies are moving away from. I am not suggesting that we exist on the 'outside' of an expanding bubble, only that we cannot visualise the entire expanding universe.

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