There’s no predestination, but the Time Lords and Gallifrey seem to stand outside of history themselves. Somehow they are able to examine the “natural” course of history, looking back from the end to see how things “ought” to have happened (despite not being at the end of time themselves), and when someone or something causes the course of history to be altered. Then they send an agent to put things “right” again.

The Time Lords are essentially meddlers, deciding how things “ought” to unfold and forcing the Doctor, who is their reluctant agent, to travel around making sure that things happen as the Time Lords have decided they “should”. Sometimes the Doctor agrees with their determination of what “ought” to be (eg, Genesis of the Daleks), other times he’s a much more reluctant agent (can’t think of an example right now).

As for why everything seems to revolve around Earth, I’ve always assumed it’s the same reason as why everyone Dante met in Hell was Italian — we’re only shown/told about the stories that we can identify with because they involve humans in one way or another.

In Doomsday, Pete Tyler says: “Every single decision we make creates a parallel existence.”

Though I never got the impression there was a parallel Doctor, so maybe he exists outside all that somehow.

Hmmm, kinda, but doesn’t “Time LORD” sound just a little more butch than that?!

More seriously, Murc seems to be suggesting that these smaller(?) changes would be therefore undetectable. I am not sure that follows; many things are chaotically interconnected in the modern world. I find it very hard to believe that there is not even the slightest relationship between significance/”poignancy” and detectablility. I can believe they are a good bit different, but mutually orthogonal? No way. (Thank goodness newspapers are dead, or changed headlines would make it obvious this dog won’t hunt.)

1. Wayne Szalinski
2. T-100
3. Chucky
4. Fred (a selectively invisible psychopath)
5. Vinny Gambini
6. Dana Scully

http://teatimebrutality.blogspot.com/2009/07/canon-and-sheep-shit-why-we-fight.html

Assuming a canon where there is none creates a lot of problems and binds up your perspective on the show in self-imposed knots.

This makes the most logical sense but is also the most dramatically unsatisfying, because it basically means that everything he does is already set down by fate.

I will note that this is a problem that can be obviated by playing for different stakes.

Cold War, for example, could simply have been about whether or not the Doctor saves the lives of a bunch of very frightened sailors, far away from home and in peril they’re not equipped to deal with. If he fails, London doesn’t turn into a smoking crater; a lot of families just never see their husbands and sons again. If anything that’s more poignant, not less.

At the meta level… we’re dealing with time travel here. It’s somewhat difficult to construct coherent rules for it that don’t fall into one of two traps; either “everything is already pre-ordained” or “time is completely mutable and the first person to travel to the past and remake the universe in their own image wins.”

I mean on the one hand there is quite a lot of stuff that is pretty much nearly canonical in the show (I hedge on this because canonical and the Doctor diverge) that asserts that traditional concepts of paradox and time travel related shenanigans are all wrong. So this would fall under that.

But since we are here, and you have asserted there are only two possible explanations I suppose I should come up with another one rather than falling back on the easy enough explanation of humans don’t know or understand as much as they think they do which is implicit in a show about a time traveling alien near immortal super-genius.

So an explanation or explanations that fits in with the show’s timey-wimeyness:

As has already been argued on this site among others and is also the argument of angels in manhattan when you don’t know how the time line is supposed to go then you can change it, just as this applies to the Doctor so it applies to any other Time Lord.

It also applies to anyone else with Time Travel abilities, or who has time Traveled.

In the Show that would be:

The Family of Blood – and perhaps whatever race they came from.

Daleks – since they fought the Time war with the Time Lords.

Some of the races that were present in The Pandorica opens might have Time travel apart from the Daleks, or they might just have hitched a ride of some sort?

Not to say that Daleks are time travelling all the time or that other races are, but it seems to be a possibility.

River Song can time travel with a vortex generator separate from the Doctor, obviously others who have these rare and dangerous tools can also.

Captain Jack can or did.

The spaceship with miniature people can time travel and go around messing with things.

Anomalous reality wide disturbances can happen such as the cracks in time caused by the Tardis exploding. Since these happen everywhen at once this changes the time, causing weird vampire fish people to come to Venice.

The Angels can send you back in time to feed off your squandered time energy.
We’ve seen them do it only with very little movement in space (relatively to moving to other planets but who knows maybe some angels sending you long distances like that as well, at any rate they can alter the timelines)

Donna had that bug on her shoulder that sent her back to change her behavior, making everything go wrong. I guess similar things can happen to other people, aliens whatever.

I could go on in the same vein as this for a while, let us just assume that I do and instead allow me to get on to other points.

If the Doctor goes somewhere historical, or someone else goes somewhere historical that can then cause repercussions that affect the future of that historical place.

We’ve also seen how, time travel being what it is, doing things in the future can have repercussions in the past because it caused someone to go to the past to escape, do something else etc.

Also not every place the doctor goes that is not specifically historical is necessarily the future. Unless a year is specified or humans are present – which they are most of the time of course – it could very well be the past on some alien world, meaning that repercussions there can send someone to historical earth. Butterfly wings flapping on Holfolax 4 can cause an alien invasion of Liverpool.

This is of course all similar to your temporally indeterminate point, it just points out that not every time traveler is the Doctor.

In fact there seems to be quite a lot of them. He’s just the best, and best equipped.

But remember that Doctor Who has had dozens of people in charge over the years. The original premise, overseen at the story level by David Whitaker, would never have seen the Doctor do more than observe events in the past. It was only later on that the difference between “preordained” and “preferred” history became part of the series’ bag of tricks as different writers and script editors had their say.

To use your example of “Cold War,” I would suggest that the TARDIS brought the Doctor to that submarine specifically because something had happened to the timeline and World War Three broke out in 1983, and the TARDIS decided that the Doctor could fix things.