me: Also, with the hotel gone, it makes no sense how Rory and Amy are stuck in NY. The prospect totally hinges on them being stuck in a building that is no longer there or guarded by an army of angels, and that the TARDIS is banned from NYC or the entirety of the world for a span of 50 years.
Her: If you think of time and space as a fabric, as some people do, or even as elastic band, the risk Amy and Rory took could have in fact tore the entire universe asunder as they had just seen Rory die, meaning that in the time line they were currently living in it had already happened. They created a new time-line where it had never happened by jumping of the building, but they could have as easily torn time. However some how they created a new time line (in theory adjacent to or on top of the current time line) in which Rory never got taken by an Angel in 195X. 195X would be the starting point of the branching of the two time lines and therefore the weakest (assuming that the two time lines stabilize out rather than collapse on each other). If Rory were then sent back there again the argument could be made that the point in time, and immediate time surrounding the 195X event is too unstable to travel to in the T.A.R.D.I.S..
The depends on how the T.A.R.D.I.S. manipulates time and space to achieve travel. And precisely what sort of damage was caused to time and space in the first place when the events happened.
me: Then if that's true, then there is a half century gap that cannot every be used in Dr. Who ever again and also retcons any other episode that has ever happened before that because of the weakened fabric of time and space.
ever*
her: No. The fabric of time exists still, in two branches (at least). Time in theory starts at one branch. So all choices made stem from that one branch.
You have to understand Doctor Who works under the multiverse theory.
Which of course covers string theory as well.
me: Even then, they visited that topic before with Tennant and Queen Victoria.
"What did you do!? I don't know! I probably haven't done it yet!"
But the whole wrench in things is the Rory killing himself paradox
Her: Yes, so in the time line the Victoria and Ten were experience simultaneously. The Doctor generally doesn't jump dimensions, just space and time. So he floats back and forth on one space line. In the case of the paradox, since the universe didn't collapse, Rory theoretically had to have created a new time line. Since that time line hasn't collapsed on ours we're out of phase with it as far as most people could define it, it's another world. This is already two worlds sitting on top of one another. If the Doctor goes back he would A. need to hit the right time line, B. need to create ANOTHER paradox by grabbing Rory again since they'd already seen Angel take Rory /and/ his gravestone.
Personally I only half buy this because the last time a paradox happened was when Rose saved her dad which caused the reapers appeared to cleanse everything and was fixed when he died anyway. I'm guessing the reapers never appeared because of the headstone incident kept the timeline intact.