doctor who and time travel
uh, so
first about time travel.
kip thorne and some people, back in the day, when thinking about time travel, decided that it could be possible.
the thing you need to know about general relativity is that it allows for spacetime surfaces where you can travel "back" in time. we've known about it since the 20's i think. anyway, there are problems with time travel and physics in general... causality in general. specifically, you can go back into the past and actively change your history. To take all the agency out of it... thorne considered a billiard ball travelling in a straight line, going through a wormhole, and knocking into its past self. so, if the ball ran into itself, and knocked itself off course, it wouldn't end up going through the wormhole in the first place! (this is the physics equivalent to going back in time and killing your grandparent).
so kip throne proposed a kind of censorship about the kinds of physical events that could occur around a time machine... a "consistency condition"... so that the only trajectories the billiard ball was allowed were ones where , if it collided with its past self, it would do so in a "consistent" way which would ensure that it's past history was consistent with the history it would create. it's easier to draw a diagram.
now about doctor who.
there is a little bit of evidence that doctor who's time travel obeys the consistency condition. for instance, his meddelling with the cybermen ensured that the dinosaurs would get killed off. and generally speaking, he allows history to work out the way it aught to (after all, the show was originally pitched at being a way to teach kids history and science). In more recent episodes, the idea of "fate" has entered heavily as a plot element in the show, and that certainly argues for the doctor obeying a consistency condition.
So what's the problem? the problem is timelord society. occasionally the doctor goes back to gallifrey and dinks around with big events in timelord history.
so here's the problem. Because timelords have LOTS of time machines, timelord "history" should not exist... the past timelord society should be as aware of the order and details of events as the future timelord society. There should be no surprises or changes... because of the consistency condition.
but, there *are* changes. I mean, there was the episode where the president gets shot and everyone is like "holy crap". and then there's the timewar with the daleks, where everyone died.
this is very interesting. It probably means that the timelords have created another time dimension, along which their history evolves, and along which they *cannot* travel. (imagine that the timelords are evolving *sideways* through the multiple-universe description).
sorting out this mystery is interesting to me, not just because i like the show, but also because I feel like It might be relevant to quantum gravity. hmmm
first about time travel.
kip thorne and some people, back in the day, when thinking about time travel, decided that it could be possible.
the thing you need to know about general relativity is that it allows for spacetime surfaces where you can travel "back" in time. we've known about it since the 20's i think. anyway, there are problems with time travel and physics in general... causality in general. specifically, you can go back into the past and actively change your history. To take all the agency out of it... thorne considered a billiard ball travelling in a straight line, going through a wormhole, and knocking into its past self. so, if the ball ran into itself, and knocked itself off course, it wouldn't end up going through the wormhole in the first place! (this is the physics equivalent to going back in time and killing your grandparent).
so kip throne proposed a kind of censorship about the kinds of physical events that could occur around a time machine... a "consistency condition"... so that the only trajectories the billiard ball was allowed were ones where , if it collided with its past self, it would do so in a "consistent" way which would ensure that it's past history was consistent with the history it would create. it's easier to draw a diagram.
now about doctor who.
there is a little bit of evidence that doctor who's time travel obeys the consistency condition. for instance, his meddelling with the cybermen ensured that the dinosaurs would get killed off. and generally speaking, he allows history to work out the way it aught to (after all, the show was originally pitched at being a way to teach kids history and science). In more recent episodes, the idea of "fate" has entered heavily as a plot element in the show, and that certainly argues for the doctor obeying a consistency condition.
So what's the problem? the problem is timelord society. occasionally the doctor goes back to gallifrey and dinks around with big events in timelord history.
so here's the problem. Because timelords have LOTS of time machines, timelord "history" should not exist... the past timelord society should be as aware of the order and details of events as the future timelord society. There should be no surprises or changes... because of the consistency condition.
but, there *are* changes. I mean, there was the episode where the president gets shot and everyone is like "holy crap". and then there's the timewar with the daleks, where everyone died.
this is very interesting. It probably means that the timelords have created another time dimension, along which their history evolves, and along which they *cannot* travel. (imagine that the timelords are evolving *sideways* through the multiple-universe description).
sorting out this mystery is interesting to me, not just because i like the show, but also because I feel like It might be relevant to quantum gravity. hmmm