I've been dueling with a twoofer over at Denialism. Can't exactly call it a debate, since I doubt it'll get into his head that "trusting Bush" isn't anywhere in my stance. I've been meaning to do a post about a key difference between science and woo: Science converges, woo diverges. Science narrows down possibilities to a handful or even just one theory. Woo, however, does the opposite: It diverges, breaking into countless hypotheses, each usually unfalsifiable. 9/11 twoofers are no exception:
R9 Orbital Wave Cannons: These twoofers are generally regarded as the silliest, though I don't quite agree. They do tend to be the most "Hollywood spectacle," though. They're the ones who believe that the finishing blow (or possibly only blow) to the towers was from some giant space laser or other impractical space opera-type superweapon that, for some reason, is never used elsewhere. It's been a while, but I'm sure if you search the JREF Forums, you could find some wonderful takedowns of this hypothesis where they calculated just how much energy, accuracy, and so forth it would take to do this. Someone gave me some points for the R-Type reference when I came up with the appropriately term.
Thermate/ite: Can't quite settle on which substance was responsible, but what they refer to is a powerful incendiary substance that supposedly melted the supports. While this has the advantage of not requiring the loud bangs you would hear in a controlled demolition, most overlook gravity: You can't get the stuff to burn sideways into the support beams. That's probably why no one I met at the JREF forums debating these trolls ever heard of a demolition team using the stuff for taking out supports. The biggest hole in this hypothesis, however, is that it'd require a massive demolitions team working for a lot of time in a building that's almost continuously occupied AND covering up their tracks every day. There's also concern about the stuff remaining stable and not igniting prematurely. Also, they'd have to deal with being able to ignite the stuff after the building has suffered a plane/missile impact that probably stands a strong chance of breaking the electrical circuit for the trigger.
Hushaboom: This is what I consider the silliest crowd, even though some may think they're the more serious type: The crowd that thinks conventional demolition explosives were used. The "hush" part of the boom comes in when some fellow skeptics pointed out the lack of appropriate seismic and audio data, which they'll claim was "muffled" or something equally silly. They may shout that it looks like a controlled demolition, but it sure doesn't sound like one. This pretty much requires that explosives have enough concussive force to take down support beams and yet be weak enough to not be heard. Contrary to what the dramatic glowing red fireballs of Hollywood fame would have you believe, heat and fire are not what makes the typical explosive powerful: It's the wave generated as the expansion of the bomb pushes air out of the way. Some may debate semantics, but air being pushed around in a wave is sound. And yet they expect these bombs to be nearly silent. To add further problems, this one suffers from the same need for invisible man-hours and technical problems as the thermate/ite hypothesis.
Missile/Holographic Plane: There are plenty of no-plane twoofers still out there who think it was missile(s) that hit the WTC and/or Pentagon. The big problem with this is that it requires that all footage be doctored and all the eyewitnesses and people with contradictory footage be wrong / bribed / silenced/ in on it. If the government had planned on doing it this way, wouldn't they have it done it in the dark to be more plausible, and less risky? The way some get around this little problem is to propose that the government developed very, very good holography before any of the industries devoting big research funding to this sort of thing can do anything really comparable. This, of course, would require a lot of setup in advance. Not surprisingly, advocates of this hypothesis will sometimes pull out claims of reverse-engineered Area 51 technology.
Let It Happen On Purpose: What I presume "LIHOP" means. This would require that Bush has direct and absolute control over everyone who could have done something or later bring up his inaction. This one's key advantage and disadvantage is that little or no planning is involved. The disadvantage aspect of it is that you can't easily identify keep the compassionate people out of the situation until something happens. It's more parsimonious than any of the nigh-supernatural hypotheses above, but it's still a hard one to swallow: It still requires a lot of people in on it.
Hire Al-Queda: This is one that I've made up myself, and about the least crazy one I can think of. Curious why I've never met a twoofer who does this one: It only requires a handful of people: The hijackers, a government officer to hire them, and some people to fake Osama's messages and hope that he doesn't deny responsibility. All they need is to exploit existing security holes that the twoofers often like to pretend we don't have, since America's so perfectly secure only we are capable of attacking us.
Now take all those hypotheses and multiply them by the number of supposed ringleaders and motives. Sprinkle in lots of combinations of who was/wasn't in on it.
Sorry I don't have links on hand at the moment. I need to get back to the JREF forums after being away for so long. Imagine it won't be hard to hunt them down, or for my regular readers to do so for me.