Once upon a time, around 15 billion years ago, time and space was created. Before that, nothing happened – nothing could happen because there was no time for it to happen in. Nor was there anywhere for it to happen. At the same instance as time and space was created, so was the stuff that turned into matter and energy we find in the Universe today. The event that created time, space, energy and matter is known as the Big Bang.
We cannot actually explain what happened in the Big Bang – the normal laws of science break down when time is not passing. But the fact that a Big Bang did occur is beyond any doubt. Astronomers have observed that galaxies are hurling away from us – and from each other – at great speeds. In fact, they are not moving through space. It is the space between then that is expanding. Imagine the galaxies as dots on a balloon. As you blow up the balloon, the dots get further apart. From the fact that space is expanding, it has been deduced that everything was once together in one ‘place’ – the ‘place’ where the Big Bang occurred. However, what was once a single point is now a huge sphere all around us.
Because light takes time to reach us, looking out into space is like looking back in time. For example, the light from Barnard’s Star takes nearly six years to reach the Earth, so when we look at Barnard’s Star we see it as it looked six years ago. It could have blown up in the meantime and we would not know yet – not till six years after the explosion. Similarly, someone living on a planet orbiting Barnard’s Star would, if they could observe the Earth see what was happening six years ago. If you look past Barnard’s Star, out towards the edge of the Universe with a radio telescope, you can ‘see’ back billion of years to almost the time of the Big Bang itself.
The revolutionary physicist Albert Einstein showed in his General Theory of Relativity that time slows in the presence of gravity. So back at the beginning of time, when all matter was so tightly compacted that its density – and its gravity – was huge, time must have passed much more slowly than it does now. So we can only begin to understand what happened in the Big Bang a short while after the beginning of time. When the Universe was just 10-41 seconds old, all matter of space, everything, was squeezed down to less than the size of the nucleus of a hydrogen atom and the temperature was one billion, billion, billion degrees.
A little later, around 10-34 seconds, a major event in history of the Universe occurred – it suddenly inflated to around 10 cm across. At this point, a flood of particles were created which would eventually form atoms. There were also neutrinos, which are ghostlike particles that can pass through the Earth as if it did not exist.
Atom –building began when the Universe was around a second old and had cooled to a more 10 billion degrees. Over the next three minutes or so, the nuclei of the lightest elements – hydrogen, helium and lithium – were created. For the next 300,000 years as the Universe continued to expand, light and other electro-magnetic radiation dominated. But when the temperature dropped to around 10,000 degrees and the matter thinned out, electrons were captured by nuclei atoms. With no free electrons to interact with radiation, the Universe suddenly became transparent. But as it was only a huge, expanding cloud of thin, hot gas there was not much to see.
As the Universe continued to expand it cooled and grew dark. Gradually the huge cloud began to break up. Bits of it began to contract under the influence of their own gravity. ‘Small’ clouds began to condense into what would one day become stars and galaxies. As these clouds collapsed further, the pressure build up at there centres increasing and set off nuclear reactions. These gave off light and the first stars began to illuminate the heavens.