September 11 and Occam's Razor

My colleague Russell Wellen has posted a missive on LIHOP vs MIHOP -- essentially the question of whether the Bush Administration, with regard to September 11, "Let It Happen on Purpose" or "Made It Happen on Purpose." These ideas seem to be creeping into the conversation about 9/11--a fact that I find dismaying. Actually that's an understatement--it greatly disturbs me.

So I am going to offer a friendly dissent, and defend the mainstream point of view: that radical Islamic fanatics flew planes into the buildings, and that direct and indirect results of the plane crashes made the buldings fall over. My dissent isn't exhaustive: anyone wanting a better one is encouraged to go here.

The principal I'm going to invoke is that of Occam's Razor--the scientific maxim that says that a minimum number of assumptions should be built into any explanation. Atheists often employ Occam's Razor to argue for evolution rather than creation. Creationism requires the assumption of a Supreme Creator; evolution does not. More radically, if you come across matted down grass in a field you know is populated by deer, you could argue that deer slept there. Or you could argue that a UFO had landed there. But this requires an additional assumption: that UFO's exist.

With regard to September 11, most of us agree that hijacked airplanes were flown into the Twin Towers (incidentally, Morgan Reynolds, the authority that Russ cites, does NOT believe airplanes ever struck the towers). It is reasonable to argue that somehow the plane crashes were responsible for the buildings' coming down. Arguing that bombs were exploded inside the building requires an additional set of assumptions: that someone (government agents, presumably) snuck into the buildings prior to the attacks and wired up explosives that could then be set off after the planes struck. Further, despite the planning involved in such an operation, no one has ever spoken of it. For the no-planes crowd, an additional set of assumptions needs to be devised about what happened to the people on the planes, and what everyone saw on CNN. That's quite an operation, particularly for government agencies that don't seem overly competent at covert action. (Since a number of these theories apparently come from a libertarian web site, we have a final contradiction: how could anyone who believes our government is so coordinated be a libertarian? Most libertarianism, after all, is built around the idea of government's inherent ineptitude.)

Conspiracy theories are often built on small anomalies in larger explanations. But not every small anomaly undoes the explanation itself. The natural world isn't uniform, and a certain amount of variation can be expected. Russ points out, for instance, anomalies in the conventional explanation: first, that "no steel-framed skyscraper, even engulfed in flames hour after hour, ever collapsed before" and second, that jet fuel does not burn at a temperature sufficient to melt steel.

Both statements are true. But jet fuel DOES burn at a temperature high enough to significantly weaken steel. Specifically, jet fuel burns at between 800 and 1500 F, while steel melts at 2750 F. But at 1100F steel loses about 50 percent of its strength, and at 1800 percent it loses 90 percent.

And yes, steel structured buildings rarely collapse. But they also rarely endure concussive shocks like those at the WTC. If we had 1000 or even 100 cases of planes flying into buildings, and the buildings always survived, then the WTC's collapse would be cause for suspicion. But we don't. Probability assessments are notoriously unreliable for new and/or unusual events. So yes, it was surprising that planes made the buildings come down, but we don't have enough comparisons with similar events to say that it was suspicious (a great example of the limits of probability and statistics with regard new phenomena was the introduction of Jonas Salk's polio vaccine, which regression analysis "proved" didn't work. The physicians, thankfully, believed their own eyes rather than the regression.)

Because large events always happen in the context of millions of smaller ones, it isn't that hard to find a series of smaller events and posit some causal relationship between them and the big event. But most if not all of these correlations are spurious. This is not just the foundation of WTC conspiracy, but also of Holocaust denial, of arguments that the United Nations is planning to take over the world, and of the American Spectator-style theories about the Clintons' violent and homicidal reign in Arkansas (culminating in the murder of Vince Foster).

Many people have much to answer for with regard to 9/11. But wild rides into the ether in pursuit mysterious CIA demolition teams distract us from the real issues, not just of culpability but also building safety and emergency preparedness. There was a lesson in 9/11 for engineers: skyscrapers don't withstand impacts as well as we thought they did. If we ignore this lesson and choose to believe instead that demolition teams brought down an otherwise indestructible tower, we will ignoring an important warning and doing a disservice to the public.

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