I’ve written a lot about how government officials lose trust when they conceal or destroy evidence of political crimes. The great thing about photographs and video recordings – especially in the age of the internet – is that these are not so easily destroyed. Government has proven that it can keep certain categories of evidence off the internet. Nevertheless, people involved in crimes have a harder time than they did before, when they try to disguise involvement.

Someday we will say, “How did we think this destruction was anything other than a controlled series of explosions?” Put another way, how could we think that gravity – by itself – brought down all 110 stories of this skyscraper? We make ourselves believe one thing, because the alternative is too awful.

Sometimes simple analysis yields clear results. Consider the pancake-zipper theory, used to explain how each tower fell straight down long after jet fuel fires ignited the upper floors. The theory has a certain plausibility, if you concentrate on certain parts of the evidence. The first key element of the theory is that the collapse of the upper floors initiates a chain reaction, whereby the collapse of each floor causes the floor below it to fail. The second key concept proposes that the horizontal trusses supporting each floor detach sequentially, or unzip from the vertical columns as the weight of the pancaking floors above come down on them. Not designed for that amount of vertical strain, the trusses detach from the inner and outer columns floor by floor, until the zipper effect reaches ground level.

Now consider the building in its standing state, where we can analyze structural integrity and vertical strength in a static setting. To pick round numbers, the columns and trusses in the first ten stories bear the weight of one hundred stories above them. The columns and horizontal supports in the lower floors bear the weight of all the floors above. That is why the column thickness at the base so exceeds column thickness near the top. The base bears so much more weight. It bears that weight securely, no matter how much the top of the building might sway due to high winds. It bears that weight securely, even if an airplane crashes into an upper floor. A disturbance, trauma, or other unusual condition at the ninety-first floor does not affect the integrity of the base. It does not affect the base’s ability to support the weight it always supported.

Now we come to a key point about this kind of structure. The force of gravity cannot “unzip” a rectangular, steel-framed skyscraper, no matter what damage occurs to the upper floors. To pretend that the lower half of a steel-framed skyscraper can destroy itself after the building suffers damage to its upper floors, is both fantasy and improvisation. No one who understands the architecture of the North and South towers can find the pancake-zipper theory believable. Steel-framed buildings are too strong to come down spontaneously or unintentionally, no matter how much damage occurs in the upper floors.

A rectangular, steel-framed tower is built to maintain its integrity in the lower floors. Catastrophic damage to upper floors does not affect that integrity. To grasp this point, compare an arch with a Lego tower. An arch has a keystone at the top, the last stone the builder places. Remove the keystone, or any other stone in the arch for that matter, and the structure fails. The integrity that gives the arch strength to hold so much weight disappears. Unlike an arch, a rectangular structure does not permit empty space underneath, but neither does it depend on every component remaining in place to retain its vertical strength. Build a rectangular tower of Lego bricks, then press down on it from the top. It will never give way. Remove some bricks three-quarters of the way up. You may have weakened the tower at that point, but you have not damaged the integrity or strength of the tower below that point.

The internal reinforcements in a steel-framed tower give the structure the same robust resistance to vertical pressure. That is why we consider skyscrapers constructed of steel, glass and concrete such a miracle of architecture, an eye-catching demonstration of our ability to conquer vertical space, and gravity, with materials so substantial we can live in the air a thousand feet above ground. You cannot make a tower constructed with steel columns collapse from the top down, by gravity or by any other natural force. To destroy a tower like that, you have to destroy the integrity of its internal reinforcements. You have to break the columns, not in one place, but throughout the structure.

One more observation: the pancake-zipper theory holds that by the time the destructive chain reaction reaches, say, the fortieth floor, the extraordinary strain on the trusses from dozens of floors pancaking down, one after another, causes all of the truss joints on the given floor to fail simultaneously. The same happens at floor thirty-nine, then thirty-eight, until you reach the ground. When you look at video recordings of the Twin Towers coming down, however, you don’t see extra weight from falling floors causing a progressive collapse from the top of the building to the bottom. In fact, you don’t see any weight at all. By the time the destruction reaches the bottom half of the building, what used to be the building above is just a toadstool-shaped ball of dust and debris. The weight the lower floors bear when the pancake-zipper theory says they must collapse, is far less than the weight they bear when the building stands in its normal state. In fact, the weight they bear near the end of the progressive destruction is almost nothing.

What then accounts for this progressive destruction, first of the building’s upper floors, and then its base? Before you answer that question, ask why clean-up workers found so much molten steel underneath the ruins at ground zero. Ask where that amount of subterranean thermal energy could have originated. It was not left-over jet fuel, which had largely burned off by the time the towers came down. It was not solar energy, or geo-thermal energy. Heat sufficient to melt steel to liquid helped destroy the buildings’ structural integrity. For each skyscraper, that energy originated in and contributed to a destructive process that began well after the buildings suffered damage to their upper floors. When the destructive process commences, you see something new in the events of that morning. The jet fuel fires do not initiate or cause the process of destruction that follows.

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