It can't be "every decision you make creates a new world" as it would mean worlds exist in which The Doctor is "Deleted" (or "Exterminated"). Even if The Doctor is immune from the spliiting of the timeline, anyone with him could cause a split unless they get a sort of Cosmic Diplomatic Immunity

Therefore the splitting of the time line must be a rare event & if so, what is the type of event that causes it?

Could it be that the actions of a Timelord cause the split and that Worlds where the Timelords didn't interfere are the "true" timeline - but that would mean the DW universe is an alternative

... Why not?

Because in virtually all possible splits The Doctor would be dead.

It would also mean that a new Doctor would be created everytime he decided to have a cup of tea or not which would kinda go against the grain of what we know about Timelords

My own pet theory is that only one version of Gallifrey existed in all dimensions and universes, which is why it was "easy" to nip between dimensions and parallel worlds - the timelords oversaw everything and monitored it all to ensure all was well.

It would also mean that there is no alternate Doctor, as timelords would exist as a single being in all realities.

But with the Timelords gone and Gallifrey presumed destroyed, the alternate worlds have become, as the Dr said, isolated.

But that's just a theory.

Its not worked out that well. Presumably alternative universes are created continually in vast numbers at the quantum level because any change has some effect and some effects are eventually significant.

That means you have lots of universes going along independently not very far apart with a whole range of differences from practically none to fundamental.

How the doctor moves along his own timeline and then changes it isn't clear to me or if someone wiser explains it it isn't consistent with what actually happens on the show. Forward travel might be easier than backwards as you wouldn't uncreate yourself but I am not even sure of that either.

Fits what Rose sees when she is in the vortex. Gallifrey has the monitoring device that doesn't kill you.

Problem then is why does the vortex blow up when it falls into another time line at the start of last saturday's trip - the vortex by definition involves all timelines so what was the problem?

My theory is the writer needs a alternative world for the plot , so he creates one.

Which is why its a bad idea as you can solve any problem by jumping ship, to a new timeline - it makes effort pointless as you will get what you want if you just keep looking somewhere else........

Want a dead dad, a carpet nail, mum and dad in love......a way out for Billie....raid other timelines.......

More lazy writing then.

Wasn't there some suggestion in Battlefield that in a parallel universe were magic exists instead of science, the Doctor had lived a life as Merlin. Or sommit.

How can it be lazy writing. DW is Science fiction and alternate universes are based on serious scientific theory.

The Multiverse theory states that an infinate number of universes exist, allowing for every possible event to take place. All things are possible. This is linked to String theory with all universes in the Multiverse co-existing side by side.

Modern physics believes that this would also negate any possible paradoxes with time travel. IE you travel in time to your past and kill your mother before you were born. In actual fact you have travelled back in time, but into an alternate universe (maybe one very similar to your own) in which you were never born because your mother had been killed. Therefore there are no paradoxes and you have simply become part of events on the alternate world.

That's what we have always been led to believe.

Sorry, but in Inferno, it is (or at least, the production team intended that it would be) strongly hinted that the Doctor was in charge of the whole country (Pertwee did the voice of the leader or something). Also, in the novel sequel to that story, (Face Of The Enemy), there's an alternate Master who has not yet become the Master.

I don't remember hearing the leader in inferno

But his picture is seen & isn't Jon Pertwee at all.
Perhaps it was just a bit of fun having Jon as his voice?
Like Ronnie Barker doing the voice of the judge that sends Fletcher down at the start of Porridge?

I was referring to the fact that as a previous poster had stated, effort becomes pointless in that case, because whatever you want to happen, you just go to a different timeline and eventually you'll find it. That is lazy writing.

The keyword in your post is theory, ie none of this has been proved one way or the other. Of course that is the point of Science Fiction, to theorise about possibilities in a fictitious setting.
One of Mankind's great strengths has been that we are able to imagine something, and then create it, ie if we can imagine it we can probably make it. I think however time travel and travel to alernative universes/timelines is rather out of our reach for the next couple of centuries at a conservative estimate. It is up to the likes of Prof Hawkings to prove his theories one way or the other.
It is interesting to explore such theories in a fictitious setting, and it is important for scientists to theorise, but theory is far from fact.
I have nothing in particular against alternate universes/timelines, in fact Inferno is my favourite story, I just would not want to see it used too often as it loses its impact and is lazy. We have already had alternate universes in "Inferno", and there are two different Dalek Timelines, possibly three now. I am not convinced it was a good idea or even necessary to use this idea with the cybermen. The original idea was that they came from Mondas, which was Earth's twin planet that had spun out into space, and then been steered back. That seems quite alternative enough, and more alternative than reusing the alternative universe idea.

But that would cause problems with the Doctor whenever he infuences events. There's a chance that his influence results in his death, therefore there are a multitude of parallel universes where the Doctor died or the results of his infuence produced different results. Which means multiple Doctors & multiple parallel Timelords

I've read it somewhere that that was what was intended. The sequel novel certainly has two Masters.

The theory is that there are some sub-atomic particles or something that behave independently of the laws of physics (ie randomly). And so to explain this you have the theory of parallel dimensions: in our dimension they move one way, and in another dimension they move another way and hence you have an infinite number of parallel realities because of all the different combinations of movements of these particles.

Personally, I think this is rubbish and I can not accept it. I think physics CAN explain why these little particles move the way they do, we just haven't found it out yet.

But I'll admit I know bugger all about physics.

The timelords (Gallifrey) existed outside of our timeline. They existed in their own timeline so I suppose they could exist outside of events and therefore only one set of timelords/Gallifrey for all universes.

I do agree that this theory doesn't fully fit in with the world of Doctor Who as he actually does travel in time along the timeline of one particular universe.

[quote=shaka01]Sorry, but in Inferno, it is (or at least, the production team intended that it would be) strongly hinted that the Doctor was in charge of the whole country (Pertwee did the voice of the leader or something). QUOTE]

I don't know where you heard this from. The picture of the leader was seen and it was not the Doctor. Also nobody recognised him in the alternative universe which fits in with the fact that there was only one set of Timelords.