or 'Things would be much easier if script writers were aware of a *small* set of rules' but who cares...
I don't remember another episode dealing with more paradoxes than 'A Christmas Carol'. Starting with the Doctor altering Kazran's time-line to Kazran hugging his younger self in the end - and surprisingly it doesn't mean the end of the world. There aren't any Reapers (we might now from 'Father's Day') and this time it also doesn't lead to the Doctor receiving doomsday-like messages from Oods or any other aliens. So what did we miss?
Although it has to be said that I think it's not us missing something but quite the opposite. Still, I suggest to keep the good old 'fans are going to sort that out somehow'-tradition up and to start with a few 'explanations'.
The most obvious and handy reason why this time the Doctor didn't need to care about the famous 'Laws of Time' was that in the 'Big Bang' two-parter the universe was whipped out and re-installed from Amy's memories. And maybe the Reapers some sort of didn't make it. Or that their non-appearance has something to do with the mysterious 'Silence'.
However, going into further detail, those lovely creatures also didn't appear in 'The Waters of Mars'. And here I have to mention the definition of a paradox, which is something along two points in time which aren't supposed to meet. Right? And fixpoints are certain events which aren't supposed to change, as seen in 'Fires of Pompeii' and 'Waters of Mars'. So, applying this knowledge, obviously Kazran's life was not exactly a fixed point in history. That's why the Doctor had some fun instead of feeling guilty while altering it.
But there is still the question why old Kazran could touch is younger self without any consequences. Well, going back to 'Waters of Mars' we know that by saving Adelaide Brooke the Doctor started off something terrifying which haven't appeared yet. Everything what happened in 'End of Time' was caused by the Master, except for the Ood's magically fast development of the ability of time travel and prophesying. Now, that could have been a result of the Doctor changing Adelaide's time-line. And this whole thing might be a hint to time having some sort of a problem in general which has to be sorted out, maybe by the Reapers. And that issue is keeping them busy for a while, or at least it appears to be a bit more important than the whole Kazran stuff. They seem to be busy saving time as we know it first, to have the time to deal with that nasty young-Kazran-thouching-old-Kazran incident. And it seems that they won't make it out of that important time-saving-job alive. So, to cut it short, whatever happened in 'Waters of Mars' may have made the Reapers cease to exist in general.
Or is it that the Reapers are just really afraid of (flying) sharks?
I don't remember another episode dealing with more paradoxes than 'A Christmas Carol'. Starting with the Doctor altering Kazran's time-line to Kazran hugging his younger self in the end - and surprisingly it doesn't mean the end of the world. There aren't any Reapers (we might now from 'Father's Day') and this time it also doesn't lead to the Doctor receiving doomsday-like messages from Oods or any other aliens. So what did we miss?
Although it has to be said that I think it's not us missing something but quite the opposite. Still, I suggest to keep the good old 'fans are going to sort that out somehow'-tradition up and to start with a few 'explanations'.
The most obvious and handy reason why this time the Doctor didn't need to care about the famous 'Laws of Time' was that in the 'Big Bang' two-parter the universe was whipped out and re-installed from Amy's memories. And maybe the Reapers some sort of didn't make it. Or that their non-appearance has something to do with the mysterious 'Silence'.
However, going into further detail, those lovely creatures also didn't appear in 'The Waters of Mars'. And here I have to mention the definition of a paradox, which is something along two points in time which aren't supposed to meet. Right? And fixpoints are certain events which aren't supposed to change, as seen in 'Fires of Pompeii' and 'Waters of Mars'. So, applying this knowledge, obviously Kazran's life was not exactly a fixed point in history. That's why the Doctor had some fun instead of feeling guilty while altering it.
But there is still the question why old Kazran could touch is younger self without any consequences. Well, going back to 'Waters of Mars' we know that by saving Adelaide Brooke the Doctor started off something terrifying which haven't appeared yet. Everything what happened in 'End of Time' was caused by the Master, except for the Ood's magically fast development of the ability of time travel and prophesying. Now, that could have been a result of the Doctor changing Adelaide's time-line. And this whole thing might be a hint to time having some sort of a problem in general which has to be sorted out, maybe by the Reapers. And that issue is keeping them busy for a while, or at least it appears to be a bit more important than the whole Kazran stuff. They seem to be busy saving time as we know it first, to have the time to deal with that nasty young-Kazran-thouching-old-Kazran incident. And it seems that they won't make it out of that important time-saving-job alive. So, to cut it short, whatever happened in 'Waters of Mars' may have made the Reapers cease to exist in general.
Or is it that the Reapers are just really afraid of (flying) sharks?