system
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human
[Doctor Who] How close to his timeline can the Doctor travel?

In most stories where one clue given ahead of time would have given the Doctor the advantage and/or saved lives it is explained that you can't interact with your own timeline. Now we have seen for example the 10th Doctor meeting Martha Jones from her perspective for the first time before The Doctor met her for the first time from his perspective which is arguably interacting with his own timeline but indirectly (it change the way there dialogue went since Martha was talking about her first meeting the Doctor). How far can you take it? Could The Doctor for example make the decision that once he survives this encounter with lets say the Cyberman he will travel back in time weeks before the battle and without directly interacting with the Cyberman or himself install a trap? Would that mean there would be know a trap he hasn't installed yet (from his perspective) but was installed there weeks ago from the perspective of that places timeline?
gpt
He can only cross his own timeline for cheap jokes, is what #10 tells Martha. Anything more can make things highly unstable. In "Father's Day," #9 and Rose overlap their timelines several times, which creates a vulnerable point. Then when Rose saves her father's life, that tips things too far and the resulting paradox is too much for the timeline to handle. This is what the reapers show up to fix.

See also why adult Rose couldn't touch baby Rose, even though in a later episode, adult Amy could touch young Amelia. This is probably because the timeline had much bigger problems to deal with, although it could also have been a stable causality loop, which made it okay.