The universe started with the BIG BANG. It is very difficult to imagine what this event was like. It is misleading to say that it was a single point in space, because it was not in space – space was in it ! It is also misleading to say that it happened because that implies that there was a time when it happened. In fact, there was no time for it to happen at. Time and space only have meaning after the Big Bang – the event of their beginning.
If you are still reading this then your head has not exploded with the totally boggling idea of the Big Bang – congratulations! You are probably in the first stage of Big Bang existentialism: denial. What evidence is there for this Big Bang? It sounds nuts. Well, the first clue was the realisation that the universe is expanding. When we look at distant galaxies through powerful telescopes, we see that they are ‘red-shifted’ – what this means is that the light they are emitting is being stretched out on its journey towards us. Light is stretched out when an object is moving away from us, and compressed when an object is moving towards us – this is known as Doppler shift. This means that the other galaxies are all moving away from us: the Universe is expanding.
The second clue to knowing that the Big Bang occurred was stumbled upon by accident, as many scientific breakthroughs are! In the early days of telecommunication, a faint and steady hiss was noticed on even the best equipment. After a long time attempting to clean up the signal, the engineers happened to mention it to some physicists at a party, and it rang a bell with them. This ‘noise’ just might be from the leftover heat radiation in the Universe about 13 billion years ago, when it was 400,000 years old, whose waves have been stretched out so much that it is now in microwave form. This was later confirmed and given the name Cosmic Microwave Background Radiation, and the two lucky engineers got a Nobel Prize.
You may have seen this yourselves – this stray radiation contributes a small amount to the distinctive noise between channels in old analogue televisions, as illustrated in the image below!
Scientists are now studying the Big Bang at a much earlier stage. Many particle physicists think that when the Universe was around 1/100000000000 second old(!), it could have suddenly “fizzed” like an opened can of soft drink. This fizz would have made gravitational waves – little ripples in space. We can calculate the pattern of bubbles in the fizz (and the gravitational waves) on big computers – like in the picture below.