Dr Who? - how or why?

[Gipsy Girl]

I wonder what would happen if The Doctor went back on his own time line and changed thing's that had happened to him.

[PTeppic]

There was a re-run of "Smith and Jones" on last night (since 42 was put back a week) and the Doctor does say they're not supposed to mess up peoples own timelines - except for cheap tricks! Which pretty much means you can but he has the experience of the possible consequences to know it's way too complex to try to do to in any major way...

[ThePeterPixie]

The Doctor has, indeed, crossed his own timeline to visit people outside of when he should (3rd Doctor visiting the Brigadier after the Brig had already met later incarnations in the 5 Doctors).
However, that was a "cheap trick" of sorts. Now I must, once again, agree with ekys and say that crossing into ones own past and making major changes would cause significant damage to the space/time continum.
As the 8th Incarnation came to realize when he saved his companion Charlie from dying when she should have. Unknowingly, he releases Zagreus (which happens to be Anti-Time) onto this Universe, nearly destroying it compleatly. So, THAT is why, based on his own experience he WON'T go back and try to change things. "Everything dies, Rose"

[Gipsy Girl]

I thought it might be some thing like that. Like The Doctor told Rose he did think about going back on his own time line to save his family but didn't go though with it.

[TiwazTyrsfist]

So, my understanding is this.

1> Having multiple instances of a single individual located in close proximity in the same time period damages the fabric of reality. For example, the fact that the Doctor and Rose went back to a time they had already gone back to once, and were so close together is what allowed Rose to change her own history. If, for example, on the first attempt Rose had tried to push her dad out of the way, it would have failed. She'd have been a second late, or he would have fallen and hit his head and died, or the like.

2> The Doctor (and any other Galafraian Time Lord) is able to coexist with other incarnations of themselves (I.E. the second, fourth, and sixth doctors say) because they are, from a physical and to an extent mental (behavior and personality) stand point, different people. Two instances of the ninth Doctor standing side by side makes holes is causality. The ninth and tenth Doctor standing side by side does not.

3> Galifray is outside normal time. A persons experiencial time and Galifrays time are linked. Galifray and the universes timelines are not. Thus, even if the Doctor were to travel to a time period when he had been able to travel to Galifray before, he could not go to Galifray, because his timeline is past the point of Galifrays fall. I.E. Suppose the tenth doctor went back to the time period when he was the Third Doctor and working for Unit. The Third Doctor could get in his Tardis and go to Galifray. The tenth doctor could not. If they both got into the third Doctors Tardis and tried to go together, the tardis would probably dematerialize, leaving the tenth Doctor standing there where it left from.

[PTeppic]

Hi,

On what basis is any of the above made?

1) There was nothing mentioned about it only being possible for Rose to save her father on the second trip; indeed even on the first the Doctor seemed aware that trying anything might be problematic, he just wasn't fast enough the second time.

2) I think this is just one of those script holes that are created when new canon law/physics is created with the ongoing development of a serial. What point is there in visiting yourself in the past - without changing something? In reality, the specials where Doctors meet previous incarnations are awful for causality and the impact on himself for knowing what to do when he gets to that situation the next/next/next time...

3) Is there any reason for saying this? He comes to Earth on multiple occasions yet IT has been destroyed in subsequent time. It's the weird concept of a time war. The only thing stopping him going back to Gallifrey is causality.