After One Salient Oversight‘s request, I’ll say a little bit more about what made me change my mind.

Firstly, the attack on the Pentagon has always struck me as odd – where is the plane? Where were the engines? How could a 767 cause such a small amount of damage? Why is there no footage of the plane striking the Pentagon? Thing is, this would be a trivial ‘conspiracy theory’ to refute – the footage taken from security cameras in the vicinity would show what happened, and they have been confiscated by the US government.

What has really persuaded me, though, is the analysis of the collapse of the two towers. I had seen a TV documentary about the collapse, which essentially told the ‘pancake’ story, ie the impact weakened the floors, causing a sequential collapse from the top down. This persuaded me at the time. What changed my mind are really simple physical points:

1) the steel would not have melted (the fire would not have been hot enough);
2) even if the steel had melted (or been weakened sufficiently), the towers would have fallen in the path of least resistance (ie fallen over, sideways), rather than the path of most resistance (ie straight down); and
3) the speed and comprehensiveness of the collapse – at effectively the same speed as a rock falling in air – shows that there was no resistance from the lower floors.

I’m really not prone to conspiracy theories. I’m sad enough to have read through the 9/11 commission report, and I was quite willing to accept that as the truth. Even now, if someone could persuade me that a plane could have caused the collapse, I’d much rather believe the official story. I no longer believe that the planes caused the towers to collapse – and therefore lots of other dominoes start to fall.

(NB the wikipedia article, and various links that I’ve chased up in the last ten minutes or so, don’t go into detail about the ‘fire’ and how it could have caused what took place, especially point 3) above. That’s the real kicker for me. I’ll keep looking though.)

Update: this is the best article discussing the physics of the collapses that I have come across.