Cues and associative memory affect our perceptions. They function as interpretive frameworks for visual evidence. Psychologists have done all sorts of experiments to test for this relationship. It turns out that remembered cues do affect the way we interpret evidence. The connection is so strong, in fact, that it can cause us to reach incorrect conclusions. That is, valid and accurately recalled cues can cause us to misinterpret evidence. That’s why it pays to compare interpretations among people who bring different cues to the same set of observations.

When frameworks help us connect familiar with unfamiliar observations, they work efficiently to help us make sense of new phenomena. The difficulty is, we don’t have a framework for what we saw when the Twin Towers came down. Airliners don’t crash into one hundred story buildings. We certainly had not seen 110-story skyscrapers explode progressively from the top down before that day. If someone speaks with authority about what we have seen, we have scant grounds to doubt the explanation if we cannot compare the authority’s evidence with something we have seen before.

After the attacks, an authoritative explanation for the towers’ destruction does not take long to come. Heat from jet fuel fires weakens the steel columns and trusses that form the skeleton of each tower. When these structural columns and their associated joints give way, the entire tower collapses in a pancake effect: each story fails after the one above it fails, due to the unnatural amount of weight coming down on top of it. Thus both towers fall straight down.

The explanation sounds plausible enough. Evidence for this kind of collapse in a steel framed building does not exist, for it has never happened before. Moreover, no competing theories came forth in the days that followed the catastrophe. The wreckage did not yield relevant evidence, so before long we had computer models to show how the pancake effect would have worked. Computer models carry a lot of authority, partly because the people who develop them seem smarter than we are. Experts and specialists usually want to appear that way.

The pancake theory has a few difficulties that make it implausible. First, the buildings’ progressive destruction does not begin at the crash sites. For both towers, the destruction begins at the top of the building. Second, the weight from the upper stories does not bear directly down. The upper stories explode multi-directionally into dust and pieces of steel. The concrete disappears into fine dust, and the structural steel flies outward. The explosions start at the top of the buildings, above the crash sites, and continue past the crash sites as they advance toward the ground. Clearly, the structural steel below the explosions does not bear more weight than it did while the buildings were whole. The explosions remove weight from the top of the structure.

Admittedly, to describe the destruction at the top and all the way down the towers as explosions begs the question. They look like explosions, but perhaps pancaking, which we’ve never seen before, looks like a progressive explosion. Pancaking would not turn all of that concrete to dust, but we can leave that point for now. Let’s take a look at another difficulty: the rate of destruction.

The rate of collapse does not beg any questions about what we are seeing. Each tower comes down in a little over twelve seconds. Using a round figure of one hundred stories for the building height, each story pancaked in about 0.12 seconds, or about one-eight of a second per story. For comparison, Usain Bolt’s Olympic time in the 100 meter sprint is 9.63 seconds. Mr. Bolt takes just over four steps per second when he runs, which means each step requires about 0.24 seconds. The pancake theory requires us to accept that, by weight alone, the structural steel in each story of these gargantuan buildings collapsed in half the time Mr. Bolt requires for one step, when he sprints at a world record pace.

Here are some more rough calculations. Each tower lost about eight stories per second. Each story in the towers was a little under four meters tall. That tells us the towers came down at about thirty-two meters per second, or three times times Bolt’s velocity when he sprints at top speed. We know how fast he runs.

Suppose each floor takes only one half second to collapse. Then the building requires fifty-five seconds, not twelve, to come down. Twelve seconds to destroy a one-hundred-ten-story, steel-framed building is awfully fast. A two-story wooden house that has burned to the point of structural weakness takes longer than twelve seconds to collapse. We know that each tower contained 78,000 tons of structural steel. Below the crash sites, each tower was structurally sound. If the architects designed a building that could collapse that fast – whatever trauma it might have suffered – they designed a catastrophically unsafe building. The idea that towers that size could collapse in twelve seconds by gravity alone is not plausible.

The interpretive framework in the government’s explanation for why the towers came down is incorrect. It refers to a pancake effect that is plainly wrong. A bit more technically, the official explanation claims that the horizontal trusses that support each column unzipped from the building’s vertical columns due to the unusual stresses placed on the building’s structural components. This explanation is equally implausible. We should recognize our mistake in accepting outlandish interpretive frameworks, understand why we erred, then work toward more plausible explanations.

An alternate hypothesis proposes that the buildings exploded, from the top down. This explanation proposes that explosions removed the core columns at the base of the towers as well. Can controlled explosions explain how the Twin Towers fell in twelve seconds – about eight floors per second – better than the pancake hypothesis? Architects and structural engineers who have studied this problem closely believe the government’s explanations for structural failure are inferior. In light of evidence and explanations available from all sources, can we reinterpret existing cues and fashion new frameworks for what we saw on 9/11? Can we rethink what we see, as well as what we perceive?

Related article

At Last, How it Was Done: 9/11 and the Science of Building Demolition