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Statement of Joshua Mitteldorf, PhD
Researcher, University of Arizona
January 15, 2007


Physical Model of WTC Collapse - Response to Garcia

Three prominent and readily observable features of the collapse of the Twin Towers on the morning of 9/11 are inconsistent with the official explanation involving fires and “pancaking”.  None of these are addressed in the Counterpunch article (http://counterpunch.com/physic11282006.html) by Lawrence Livermore physicist Manuel Garcia.

First, the towers collapsed quickly – more quickly than even Garcia’s highly optimistic calculation can account for.  Though he gives the government’s account every possible benefit, he calculates a terminal velocity that is less than half the speed required to explain the collapse we see in the video.

Second, the collapse was symmetrical.  Natural events (including fires) will always be governed by a certain amount of randomness.  Some situations are stable and inherently restore symmetry; but the collapse of a tall building is not one of them.  In fact it should not take a physicist to realize that tall, slender objects will always fall to one side, absent some very carefully controlled circumstances.

Third, each collapse began with an explosion in the upper stories that carried impressive energy.  Jet fuel will burn, but not explode.  This is because jet fuel or any fuel can only burn as fast as oxygen can be circulated into contact with it.  Explosives, on the other hand, are designed with a single chemically unstable compound, or with two reactive components that are pre-mixed on a microscopic scale.  The explosions that are readily observable in videos of the towers’ collapse could only have been produced by commercial explosives.

The first point concerns the speed of the collapse.  Garcia models the standard “pancaking” theory, in which each floor falls upon the one underneath, and the strength of the supporting members on that floor proves insufficient to break the fall.  He makes assumptions about ideal behavior that are appropriate to physics textbook examples, but inapplicable in real life.  All these assumptions tend in the direction of making the collapse appear faster than real life circumstances would allow.  Still, he arrives at a terminal velocity of 46 m/s.  Since the towers were 440 m tall, this implies a time of 19 seconds (2*440/46) when in fact the videos showed that one tower collapsed in about 11 seconds, the other about 12.  Garcia must have realized that this discrepancy would be an embarrassment, so he never completes the calculation.

“Free fall time” refers to the time it would have required for the towers to collapse if all supporting structures suddenly and simultaneously disappeared.  Free fall time for 440 meters works out to 10 s, and the actual collapse times were so close to free fall time that we must conclude that this is what happened.  The beams at the bottom of the towers lost their strength at precisely the same time as the beams near the top.  This would not have happened in a natural fire of any kind.  It implies a feat of engineering.

The second point concerns symmetry.  We are all familiar with the way tall, slender structures fall.  A pencil may be highly symmetrical, and will stand for a time on one end; but any tiny push to one side will cause it to topple over sideways.  To bring down tall steel structures symmetrically requires an impressive feat of engineering, and would never occur by chance.  There is a well-developed science of controlled demolition, and only a few firms in the world would take on the challenge of placing explosive charges and timing their detonation so as to assure that a buildings as large as the Twin Towers would fall straight down.

The maximum combustion temperature for jet fuel is 1000 Centigrade, far less than the melting point of steel.  Paper, wood and other materials in the towers would have burned at yet lower temperatures.  It is not plausible that fires would weaken the steel sufficiently to bring down the Twin Towers; but if this were ever to happen, it would occur in some places before others.  Certainly the members on one side of the building would reach the temperature at which they yield a little earlier than the members on the opposite side, so the building would topple sideways, and not straight down. 

Third, no explanation has ever been put forth for the explosions in the upper stories of the WTC towers.  These explosions turned concrete to dust, and sent heavy pieces of the wreckage flying through the skies over Manhattan for over ½ km.  This was not a jet fuel fire, but a massive explosion.  Our own eyes tell us there were explosives in the buildings, and they were detonated in a process precisely timed to the collapse of supporting structures hundreds of meters below.

Finally, I mention only for extra emphasis that a third tower (WTC 7 [570 feet tall, 47 stories]) collapsed 6 hours after the first two.  It was never struck by a plane, and fires in WTC 7 were far smaller than the other two towers, and confined to one side of the building.  Yet WTC 7 also collapsed suddenly and symmetrically, almost as fast as a free fall – hallmarks of controlled demolition.  The 9/11 Report of the Kean Commission omits any mention of Building 7, and no government agency has even proposed an explanation of how it fell.

Conclusion: We may differ over the political plausibility of conspiracies that have been proposed in connection with the destruction of 9/11.  But the physical implausibility of the official scenario concerning the towers’ collapse should be beyond dispute.  This is an area where physicists’ calculations and our commonsense notions of how tall objects fall down both point to the conclusion that sophisticated engineering and carefully-timed explosive charges would be required for the towers to fall in the manner that they did.

You don’t have to be a rocket scientist to understand why the official account of 9/11 is physically unreal, but as it happens, author Josh Mitteldorf has a PhD in theoretical astrophysics.

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