The Big Bang!Wow, what a start to the universe! A huge deafening explosion of cataclysmic proportions, I am so impressed!!
Well actually, no... not exactly.
First problem is that as we all know, the famous film quote goes something like 'in space no one can hear an ice-cream van', something like that, I can't remember exactly.
So, no noise.
And no explosion. An explosion needs to have somewhere to explode into and there isn't anywhere because it's all nothing... Until the Big Bang creates a rapidly expanding universe, which fills the nothingness... well no because it can't fill something that wasn't there before... and no, it wasn't just empty space before then because there was no space... Aaaaarggghhh - ok, that's a problem us humans have in trying to visualise stuff that goes well beyond our 4 dimensional existence!
Lets just think from within the universe which after the 'big bang' rapidly expanded.
It's thought that everything originated from a relatively very very small existence.
That's partly possible because everything is mostly made up of... nothing. At the heart of an atom is the nucleus surrounded by electrons but they exist in a relatively vast open space - if you imagine the nucleus to be the size of a grain of sand then the space surrounding it containing the tiny electrons would stretch out to the size of a large house. But the main reason that it's possible to compress the universe so small is that all known laws of physics break down at that point and anything is possible, including multi dimensions, time travel, etc.
How this actual pinpoint of everything appeared in the first place we will probably never know, so there's still plenty of room for religion, philosophy, etc.
This tiny pinpoint singularity was unimaginably hot and in a constant state of flux at speeds beyond our understanding and may have existed for an infinite time (or more likely outside of time). But something happened to suddenly cause a chain reaction in which energetic light photons gained control causing a very rapid expansion.
In the first few micro-seconds very basic particles which we now call Quarks were created and fired out in countless numbers creating a thick blanket of basic matter. They then quickly started to join together to form neutrons and protons. It then took just a short time later for those to start to clump together and drag in electrons to form some of the basic atoms that are still widespread through the universe today, such as Hydrogen and Helium.
As the universe expanded it gradually became diffused enough to allow light photons to pass through. Whether you are religious or not, the phrase 'and God said let there be light' is probably an apt way to describe those early moments.
Note: Could the Big Bang theory be wrong?
There are a few issues with the theory. For one thing there's the problem of the missing 'dark matter' which needs to exist for it all to make sense but can't yet be found. There should also in theory be a universal equivalent amount of anti-matter present, but there's no sign of any at all. Lastly, unlike other explosions where the outwardly flung material would gradually slow down, our universe actually continues to accelerate outwards!
So there are other theories, but all we can do for now is just look at the evidence and calculations available today and these currently appear to reinforce the Big Bang theory.
PS: Where is the centre of the universe?
As it started with an explosion 13 billion years ago you would think that there must now be a vast centre point which is totally empty because all the matter keeps expanding away from it. The difficulty is that the Big Bang wasn't actually an explosion in the same way we know other explosions. It was more of an instant creation of the universe itself and therefore you can't find the centre of the universe where it all began because the universe wasn't there when it all began!
(... I can't understand that either..)