As the 10th anniversary of the Sept. 11 tragedy approaches, there will be remembrances, speeches, documentaries, vigils and other reflections of that day. I also anticipate a resurgence of claims that the attacks were not executed by Islamic extremists, but rather the result of a large-scale conspiracy orchestrated and covered up by the U.S. government, Israel or some other vaguely defined entity.

Almost immediately after the attacks, there were claims of planted bombs, missing planes, fired rockets and other suspicious events. Books have been written, websites are devoted to the topic, underground movies have been distributed and fliers are still handed out at ground zero. This buzz of activity may lead even skeptics to wonder if there really is something behind these claims.

Perhaps the most oft-repeated claim is that the World Trade Center towers were not demolished by the airplane strikes and the resultant fires, but from explosives planted by the true perpetrators. After all, the buildings did not tip over but rather fell straight down, similar to what is observed in a controlled demolition by professionals who use explosives to raze buildings. People heard explosive-type sounds as well.

As a scientist and science educator, I am dismayed at how infrequently people employ the scientific method to address complex problems. The scientific method formulates a hypothesis, gathers information to test that hypothesis and then accepts or rejects it based on the findings. The beauty of this approach is that anyone can use it. It involves establishing facts, not relying solely on initial impressions, and sometimes abandoning intuition if the collective evidence mandates it.

Addressing the controlled demolition hypothesis is easier than it may seem because experts have studied and written about the collapse of the twin towers. Brent Blanchard, a demolition contracting expert with Protec and who worked at ground zero, said the tower collapses were only superficially similar to a controlled demolition. For a demolition, explosives are placed in the lower part of the building to cut supporting beams. As a result, the building initially gives way at the bottom, and most of the destruction is due to the building collapsing on itself due to gravity, not by blowing it to smithereens.

By contrast, the World Trade Center towers failed initially much higher, at the site of the fires, and moved successively downward. The lower parts of the towers remained intact until they were crushed by the falling part above. I convinced myself of this by comparing YouTube videos of controlled demolitions to the twin tower collapses. I recommend the Landmark Tower demolition because it provides sound as well as video. The detonation sounds are brief and in rapid succession, which differs from what World Trade Center witnesses reported.

Could the collapses have been caused by an atypical controlled demolition with the explosives placed near the airplane impact? MIT professor Thomas Eagar explains that the fires would have been sufficiently hot to weaken the steel columns so that they could no longer support the million of pounds of building above them. This means that the fires accomplished what explosives could have done, and so there is no need to invoke explosives as an explanation. Although our intuition may tell us that the towers should have tipped over rather than fall straight down, engineers know better. Buildings are composed mostly of empty space, and the path of least resistance is straight down. This explains the superficial similarity between the World Trade Center towers and a controlled demolition.

How else can one test the hypothesis? Detonations can be detected by seismographs -- machines used to measure earth movements such as earthquakes. Researchers from Columbia University were recording seismic activity in Manhattan at the time. They recorded tremors caused by the falling buildings, but no prior signals expected of detonations were observed. These recordings are publicly available online. Also, explosive demolitions leave all sorts of telltale signs that were not found in the ground zero rubble, according to demolition expert Bill Moore, former president of the National Demolition Association. Not only are the cuts to the metal distinctive, but blasting caps, detonation cords and other debris would have been found, but were not.

Stephen Jones, a professor emeritus at Brigham Young University, reported traces of a substance called thermite on a steel beam section taken from ground zero to be used in a Sept. 11 memorial. However, Blanchard notes that thermite is not used, nor would it be useful, in a controlled demolition. Since thermite can be used for welding and cutting steel, it seems more likely that thermite would result from removing a section of beam from the ground zero site.

The collective evidence argues that the controlled demolition hypothesis should be rejected unless new information arises. Is it possible that the hundreds of people in the public and private sector who have studied the causes of the collapse of the World Trade Center towers and worked on site are all involved in a coverup?

The problem with this assertion is that a coverup is itself a hypothesis that must be tested. To invoke that idea without evidence is scientifically unsound, not to mention lazy. The coverup claim concedes a lack of evidence in support of a controlled demolition, and instead tries to maintain that hypothesis by a perceived inability to rule it out. This is called a negative argument, and it is scientifically unacceptable because it can be used to espouse any idea no matter how unlikely. One could use a negative argument to insist that there are little green people inside the moon simply because it has not been formally ruled out.

There will be many emotions and reflections associated with the Sept. 11 anniversary, but hysteria over unfounded claims does not need to be among them. In this regard, perhaps the scientific method can provide a small measure of solace.


Mark R. O'Brian is a professor of biochemistry at the University at Buffalo.