In a number of occasions The Doctor explains "Fixed Points", moments in time which cannot and/or should not be changed, examples of these are the eruption of Mount Vesuvius (The Fires of Pompeii), the destruction of Bowie Base One (The Waters of Mars), and the 11th Doctor's death at Lake Silencio (Series 6)

We know what happens if someone tried to change a Fixed point,

  • Time fixes it up as it did when the 10th Doctor saved the crew at Bowie Base One, who were supposed to have all died, however the event is made public and Adelaide Brooke committed suicide to preserve the timeline

  • Time would collapse, unable to repair the fixed point on its own, as when River Song refused to kill the Doctor at Lake Silencio (eventually is fixed when the Doctor revealed to River Song his plan showing he was actually inside the Teselecta at the time)

However, I can think of 2 events which could have ended humanity which predate the events of Bowie Base One:

  1. In Daleks in Manhattan, had the Daleks been successful we can probably assume that eventually humanity would have been wiped out or at least enslaved to be used to create new Dalek Hybrids.

  2. In The Poison Sky, the Tenth Sontaran Battle Fleet planned to convert Earth into a cloning world. They released Sezerfine gas, poisonous to humans, so we can probably assume that had the Sontarans been successful humanity would have died.

These events predate Bowie Base One both in time they occurred and in humanity's technological advancement (the 2nd point, despite the existence of UNIT and Torchwood there wouldn't have been any planned/ongoing missions to set up a base on Mars).

I am wondering what would have happened to a fixed point in time if the past were altered so much that said fixed point couldn't possibly happen?

  • 2
    What kind of answers are you looking for? I don't see how this could be answered except with personal theories. Sep 29, 2014 at 0:45
  • @curiousdannii anything that's been explicitly explained in supplementary material has i've only seen the arc which has the Doctor meet Davros for the first time on Scaro and all the episodes from Rose being a companion onward. i'm quite sure personal theories are fine here so long as one backs up the theory with evidences (ie. using supplementary material) that way it's not entirely an opinion based groundless answer but more of a connect-the-dot kind of thing
    – Memor-X
    Sep 29, 2014 at 1:15
  • 1
    Again? Look I explained this to you next week, it's really quite simple; what seems to be a strictly linear progression of events... Oct 10, 2014 at 4:09
  • @Memor-X perhaps those attempts were destined to fail precisely because they would alter future fixes points, and had the Daleks or Sontarans been more time-aware they would have known not to bother.
    – KutuluMike
    Oct 11, 2014 at 21:27
  • 1
    I suspect that the answer is "Whatever the showrunner wants". Showrunners have the power to create and ignore fixed points in time.
    – Blackwood
    Apr 19, 2017 at 0:38

3 Answers 3


I know its an old question, but I'm surprised nobody mentioned the episode 'Turn Left'.

This indirectly shows us how fixed points, and 'changeable ones' work. I don't think we need spoiler tags, as its a very old episode.

Donna's history is rewritten by changing a key point in her history. IE she never met the Doctor, as a result the doctor dies under the Thames. We also see that even with the Doctor dead, those world ending scenarios didn't end the world. The Torchwood team stopped the Sontaran, Sarah Jane stop Jadoon.

This gives us a lot of insight into how time can rewrite itself. Speculating here but this seems to imply some things:

  • Non Fixed points shift in little ways, to ensure the fixed point will happen (one way or the other). Bear in mind that its ONLY the fixed part that cant change, small things can be done. E.G Pompaii the fixed point was the explosion, not saving people or anything else (even if the Doctor didn't do it something else could of, maybe a meteor would be nudged off course to cause the explosion, who knows).
  • Time is only damaged if the fixed point CAN'T happen in some way. IE small changes/corrections to the timeline, can't be adjusted for (Like the Doctor not appearing to die by the lake).
  • The time between 2 fixed points gets bend to make the next one happen, even if its not exactly the same (Only the fixed part of the event has to happen, nothing else).

So to conclude. It seems that all events between 2 fixed points can (and do) change, to make sure the fixed point happens in some way. I read a good example given in another post. As HNL described it in this answer

Time in the Doctor Who universe appears to be like a rubber band that is anchored to fixed points at certain critical places. You can pull and stretch it, but it'll snap back. Pull too hard and it breaks catastrophically.

If anybody knows who wrote that I'll give credit.

Also, we are never told what the actual fixed point is. Think about it this way, if Pompaii is just the Volcano it could have happened with no life on earth. If the Doctor had to appear to die by the lake, this could be a hologram, without Amy or River seeing it. Even the Mars base, a small Silurian colony could be what blew up (as long as a base disaster happen there, and then). Its the fixed point ONLY that has to happen, not the details.

Just my thoughts based on whats shown onscreen. Hope I've explained this well enough, its a hard concept to try to write down.

Edit Found where I read the rubber band description, link added and credit given to HNLs answer


Temporal mechanics in Doctor Who isn't that concrete. It changes regularly based on what they need from it. The best explanation I've heard is that it's just a load of wibbley-wobbley timey-wimey stuff.

It's not helped by the fact that temporal mechanics is all strictly hypothetical anyway, delving into realms of metaphysics where we can't tread yet. Leave it to The Doctor, they seem to know what they're on about.


I suspect the universe takes a hard fork and a new timeline grows new fixed points. In the Tom Baker era Pyramids of Mars part 2 this is demonstrated-wiki summary "Sarah suggests they should just leave in the TARDIS, because they know that the world did not end in 1911. The Doctor demonstrates otherwise by moving the TARDIS forward in time to 1980. There, the TARDIS doors open to reveal a blasted wilderness, with thunder, rain and lightning hammering down on to ash fields. Sarah understands that they have no choice but to return to 1911 and stop Sutekh, or the future will be lost."

The rest of the universe is always changing in small ways around the fixed points. That's why Gallifrey was always watching to keep the entire timeline the way they wanted it to be. I use sand dunes as an analogy. It seems like they are permanent but they drift and disappear.

The Daleks for example are something relatively new. They haven't been the enemy of the timelords for 8 billion years of Gallifrey time. They are something that became unchangeable in the Doctor's lifetime and became a rival time traveling civilization.

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