I focus on one question: why the Twin Towers and building 7 of the World Trade Center collapsed. One advantage of this focus, besides the fact that it allows us to go into considerable detail, is that the destruction of the World Trade Center provides one of the best windows into the truth about 9/11.
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The official theory is rendered implausible by two major problems. The first is the simple fact that fire has never—prior to or after 9/11—caused steel-frame high-rise buildings to collapse. Defenders of the official story seldom if ever mention this simple fact.
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The most important thing in a controlled demolition of a tall building close to other buildings is that it come straight down, into, or at least close to, its own footprint, so that it does not harm the other buildings. The whole art or science of controlled demolition is oriented primarily around this goal….If the 110-story Twin Towers had fallen over, they would have caused an enormous amount of damage to buildings covering many city blocks. But the towers came straight down. Accordingly, the official theory, by implying that fire produced collapses that perfectly mimicked the collapses that have otherwise been produced only by precisely placed explosives, requires a miracle.
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The collapse of building 7 is even more difficult to explain than the collapse of the towers in part because it was not struck by an airliner, so none of the theories about how the impacts of the airliners contributed to the collapses of the towers can be employed in relation to it.

The primary logical fallacy committed by 9/11 Truthers like Griffin (and most conspiracy theorists in general) is exclusion, a form of selection bias that basically means “evidence which would change the outcome of an inductive argument is excluded from consideration.” Exclusion is one of the most dangerous fallacies. It closes down the mind to rational inquiry while still maintaining the guise of concern for evidence and truth. Most 9/11 Truthers, for example, maintain an image of genuine curiosity and a desire to know what really happened, claiming that they’re “just asking questions.” Their commitment to a predetermined conclusion, however, keeps them from ever being satisfied with the answers.

Essentially, it’s a reverse of the scientific method: they’re starting with a conclusion and then looking for the evidence. The collapse of Building 7 is a good example of this. 9/11 Truthers are already confident that it was a government-controlled demolition, so they look for evidence to support this claim. If they were merely looking for an explanation of Building 7′s collapse, would government-controlled demolition be at the top of the list of options? Much more reasonable explanations for Building 7′s collapse exist. Even if the government wanted to take down the two primary WTC towers in a controlled demolition that wouldn’t damage nearby buildings, why would they also need to take out Building 7 in a controlled demolition? What would that accomplish? Who would it help? It doesn’t make sense unless you’re starting with the idea that the government planned the whole thing–and then work backward to show selected evidence for why you think what you already do.

The evidence that Griffin and others have to ignore is massive and detailed. In the case of Building 7, he relies heavily on an early FEMA report that cited relatively minor damage to the building before its collapse, partially due to the fact that heavy smoke and ash prevented a clear view of the structure. Later evidence and research from NIST, which the 9/11 Truthers ignore, shows that the debris damage to Building 7′s south face was far more extensive than originally thought, there was significant damage to 10 lower stories, and the building’s collapse is explicable apart from conspiracy theory. If the Truthers choose to ignore workable, comprehensive explanations for Building 7′s collapse, they should at least be able to provide a workable, comprehensive government motive for destroying Building 7 along with the other towers.

There is also good evidence and explanations for exactly how and why the twin towers collapsed. Each of Griffin’s objections is answered by a simpler, less conspiratorial account from chemists and physicists who have examined the events. For example, jet fuel burns at 2190 degrees, 560 degrees lower than required to melt steel. Yet “steel weakens at as low as 400 degrees; at 980, it’s at only 10 percent strength,” according to industry experts. The steel frame didn’t have to liquefy before it was going to collapse.

One fallacious assumption leads to another, and the conspiracy builds on itself. After the bare assertion that the twin towers “perfectly mimicked the collapses that have otherwise been produced only by precisely placed explosives,” it’s easy for Griffin to ignore the damage done to Building 7 by the collapsing twin towers and say that because the twin towers represented a perfect controlled demolition (which they didn’t), we have no explanation for how Building 7 collapsed. You can get almost anywhere simply by starting with one false premise.

In summary, alternative explanations can always be devised (almost ad infinitum) for why a certain event occurred. (Hell, 9/11 could have been the work of aliens.) This is why determining the most likely explanation–with principles like Occam’s Razor–is so important. As Carl Sagan famously said, “Extraordinary claims require extraordinary evidence.” If you are going to assert a massive conspiracy theory, a massive amount of evidence will be required in order for your theory to triumph over the sufficient and evidence-based “official explanation” that is currently in place.

Questions are a good way to probe and discover truth, but unanswered questions are not proof that a random other theory without supporting evidence is automatically correct. If unanswered questions exist (and in this case, they really don’t exist anymore), all it means is that more investigation is required. Sentences beginning with, “The only possible explanation is that…” are usually signs that the speaker is trying to push an idea without supporting evidence into the hole that exists in our current understanding of a situation. “Alternative” explanations can always be devised. Proper conclusions begin with phrases like, “The existing evidence strongly points to…” and the 9/11 Truthers don’t have evidence. They have obsolete gaps that have been filled in with good evidence for years.