I found "Mere Christianity" by C.S.Lewis a great help.

There are lots of possibilities.

The god who created this universe could have been created by another god who doesn't deal with this one.

We could have been created by a god who isn't able or interested to interfere with the processes from within its creation.....Like a programmer who once they create a large enough program can't tell you exactly what's going on within the program at any one instance.

So many possibilities....Perhaps we are crabs at the bottom of the rockpool looking up at the surface regarding the ripples from raindrops as messages from a creator.

Hang on...that sounds like I'm on a spliff......when I'm actually trying out this new strong coffee from Tescos.

'Who are you and how did you get in here? I'm a locksmith. And, I'm a locksmith.' (Leslie Nielsen)

It's Islamic, but nothing to do with Islam?

Murdered for blasphemy, but nothing to do with the religion he blasphemed against?

Is this comedy or what?

Or god doesn't exist, and we're mearly ascribing events and phenomena we might not understand, but can be explained in very complicated ways.

"One Nation Under God, has turned into One Nation Under the Influence of One Drug"
[Link]

Firstly, it can only 'happen' spontaneously, as prior to the big bang, there is no dimension of spacetime. Prior to this, everything exists that exists now - without space and time (see quantum theory).

Now why that occurs (and it might not occur, it might just simply be that we're experiencing it from an internal perspective of existing within space and time - as from high dimensional topology objects in space time are different ie from a fifth dimensional perspective time is occurred not occuring) is the question.

However that 'big bang occured' only applies to a perspective within space-time as a dimension (i.e. we are simply see it as occurring, because we're a part of the process of something that has already occurred for a brief time.

Or if it was an event that causes big bang (and the term causal is reliant on time and space events), such as how dimensions function within a reality, how realities exist etc.

However, none of this requires god, or a creator or event really an event to trigger big bang. We call it big bang, as its a convenient method of explaining a very complex series of theoretical models, which are evidenced by astrophysical research, quantum and relative physics.

What really happens with big bang is that subatomic particles go from being in a null state, to the state we are experiencing them in (which is a state of entropic change that will result in an end state) - but we are also part of that entropic change.

From a 5th or higher state, that 'change' has occurred (much in the same way that we see 2D and 3D models as being constants, the same applies to 4D from a higher dimension).

But none of this requires a god. Prior to big bang everything existed, after big bang everything still existed, and we're a part of that process (briefly).

We're kind of like a Salmon in a stream trying to understand what land is.

"One Nation Under God, has turned into One Nation Under the Influence of One Drug"
[Link]

I've subsequently seen that Jamie has fully quashed any belief in some bloke with a big sciencey answer!