Why did the Daleks bother to leave Adelaide Brooke alive?

Question

In The Waters of Mars, it is shown that a Dalek left Adelaide Brooke unharmed when she was young during the events of The Stolen Earth, because she was a "fixed point in time", according to the words of the Doctor.

However, if they had succeeded in stealing the Earth (and they rather planned on it by taking any action at all) the future that is written for her (death on Mars on the first off-planet base) couldn't ever happen because there would be no more Earth in the solar system (nor humans, etc.), so leaving her unharmed is quite senseless.

Similarly, if she has to die on Mars she needs first to get to it, so when the Daleks spot her and realize the fixed point issue, why didn't they just abandon their whole plan as it has to fail to allow events of The Waters of Mars to happen?

Answer 1

It's probable the Daleks did not know what that fixed point in time would be -- perhaps she would turn out to be a fixed point in time in the future they were bringing about. They can't see the future, but apparently had some notion that it would be "wrong" (in the sense that Captain Jack is "wrong") to kill her.

It isn't stated what exactly the criteria are for making a point in time fixed. If there are rules, they may not be revealed to the audience. More likely, "fixed points" are entirely plot driven and in-universe explained just that certain time travelling characters/species are able to "feel" in some way.

I don't think we have enough information to say how much the Daleks knew -- perhaps they just got a queasy feeling and decided it was a bad idea without ever formalizing the thought "oh, hey, she's part of a fixed point in time".

The whole "fixed point" concept is firmly in Timey-Wimey ball territory; the only decent explanation in-universe is that the concept is too advanced for us to understand on any meaningful level either because of our relatively primitive science or because of a lack of some sort of temporal physiology. Out-of-universe, it is a mechanism to allow writers to sometimes block the Doctor from tinkering so much with time.

Answer 2

In Moffat's who, fixed points are fixed by the fact that time travellers remember them; remember the last scene of Girl in the Fireplace. The kicker was that Madame de Pompadour wasn't just another queen in a history book, she was someone timeships were named after. So the doctor naturally could never arrive at the right time to keep his promise.

Changing a fixed point remembered by everyone in the future, time-capable human empire would have started a new mini Time War with that empire. Resulting is a fleet full of 51st century battle cruisers showing up and interfering with the daleks plan.

Making the decision to start such a war would be above a typical Daleks pay grade.

In contrast, the genius of the whole 'destroy every possible universe' plan was that it wouldn't have left any time travellers around to come back and undo it...

Answer 3

A dalek might be able to recognize a fixed point, but can they see the future that fixed point creates or is related to? Daleks have never (to my knowledge) demonstrated precognitive ability.

Essentially, the dalek in question knew that killing her would create a paradox (generally considered a Bad Thing™), but did not know what leaving her alive would result in. Taking an unknown future (which may not have even been a negative for the daleks) to avoid a bad present is a logical course of action.

Answer 4

Maybe the Daleks have no notion of the fixed time issue except Dalek Caan. He is the one condemning the Daleks in the end because he saw through time itself. It would be only logical that he also saw the future of Adelaide Brooke and her importance in time or even her importance to the Doctor. Only through her he did not become the timelord victorious, who could have made even greater damage to time. Being amidst the Daleks and with Davros doing everything as Caan said, it is possible that he ordered them to leave Brooke (and maybe other important persons) alone for the "prophecy" to fulfill.