A short post regarding my recent catch-up on Doctor Who. Warning: Spoilers up to 07x13 "The Name of the Doctor."
So at the end of the fifth season, the TARDIS explodes with River Song inside of it. Question: Why did the TARDIS explode?
We know that River Song wound up back at Amy's house on 26 June 2010. She called from that time to tell the Doctor what she discovered there. Meanwhile, Rory tries to get Amy to recognize her. The engines of the TARDIS start to shudder. Something's wrong, and then "silence will fall" is heard. River says that she thinks an "external force" is at work, causing the TARDIS to fail. That is why she can't leave 26 June 2010, and that's why River can't even get outside of the TARDIS. She's sealed in.
Later indications suggest that "the Silence" is a race, or a movement, or something, that want to stop the Doctor. Thus, the implication is that "the Silence" has managed to capture and/or sabotage the TARDIS to explode. The trouble is, the exploding TARDIS precipitates the end of the universe, and "the Silence" doesn't want to destroy the universe, just to stop the Doctor. On top of that, the TARDIS isn't just a ship, she's a living entity that often drags the Doctor off without even telling him.
So the implication (although not officially explained) is that "the Silence" sabotaged the TARDIS to explode on a fixed date, 26 June 2010, so that the Doctor's enemies would lock him in "the perfect prison" of the Pandorica. That sounds all nice and good, especially because if the Doctor escapes and fixes the universe, he would die in the cataclysm of the reboot. However, while the Doctor might be a hard man to kill, all his enemies in the universe showed up and locked him in the Pandorica. Seems a little feeble, doesn't it? I mean, every enemy he has agrees he's so dangerous he needs to be stopped, and... they lock him up? He might be a hard man to kill, but that trap they set for him was quite literally perfect. He had no recourse. Instead they entrap him in a prison so perfect that you can't even die in it? Sounds more like they were storing him for later, not stopping him.
So that basic implication is lame. And a bad story. So, alternatives?
"The Silence" has since been shown to have their own time technology, not to mention a terrible powerful influence that no one can ever remember. They could have influenced that alliance for all of the Doctor's enemies to lock him away - not to kill him, but lock him away, without the TARDIS exploding. No time cracks necessary!
So... then why did the TARDIS explode? Simple: paradox.
The Silence had many good plans, sure, but they either poorly accounted for, or failed to account for, the Doctor's wife, River Song. She was in the TARDIS on the date 26 June 2010. Later this date was revealed to be her conception date (the night of Rory and Amy's wedding). The TARDIS's engines started to go, but the actual explosion didn't happen until after Amy Pond was shot and slipping away.
Rory was erased from time and space, but his engagement ring to Amy remained. It's logically possible, then, that Amy could have already been pregnant; and since she and Rory didn't really have time outside the TARDIS, conception was likely to have taken place on the TARDIS. Therefore, after Rory disappeared into space and time, River Song still existed.
So the Silence get the Doctor locked away, great. But meanwhile, Rory's Roman Clone shoots Amy Pond and kills her; therefore, River Song was never born. This might be just fine and dandy in some situations, except that River Song is in the only place in the universe that could handle such a paradox: the TARDIS. The TARDIS could've been compensating for the disappearance of Rory from time and space to protect "the child of the TARDIS," River Song... but handling the paradox of Amy Pond dying without having had a daughter was too much. In 06x10 "The Girl Who Waited," we discover that there can't be two Amys in the TARDIS. The paradox is too massive. We also learn that a paradox can tear large areas, even entire planets, apart. The question is, could the TARDIS handle a paradox like River? If she wasn't born, then a dozen other paradoxes open up in the Doctor's time line. Not only is she a child of the TARDIS, she's a time traveler in her own right. And it's clear that the TARDIS loves the Doctor and quite possibly River as well. That being said, even the TARDIS has limits... only so much paradox can exist. So the TARDIS tries to maintain the paradox that is River Song, but in so doing generates an even more massive paradox. This causes the explosion.
Really big paradox that the TARDIS wants to handle, but can't? Big explosion.