Email interview with Dr. Zdenek P. Bazant

I have had the following discussion with Zdenek P. Bazant, co-author of
the 9/11 Twin Towers collapse theory article titled "Why did the Twin
Towers Collapse -- Simple Analysis." Unfortunately he has not answered
all of my questions regarding his model of the collapse, probably just
because he is busy or not inclined to do so. I am sure it is not
because he is unqualified to answer my questions or because he is
involved in deliberately misleading the public about the nature of the
WTC destruction as part of some conspiracy or something. So, I am
asking any physicists or engineers if they can shed light on this
subject. I would like to be able to understand how Dr. Bazant's theory
explains the utter destruction of the Twin Towers in the manner recorded
and witnessed on September 11, 2001.


> Date: Friday, May 4, 2007
> Subject: Re: Regarding your WTC collapse hypothesis
> Dear Professor Bazant,
> I have read with interest your 2001 paper entitled "Why Did
> the World Trade Center Collapse?—Simple Analysis". I wonder
> if you might take some time out of your busy schedule to
> satisfy my curiosity.
> Your paper mentions that the towers collapsed because the
> higher floors would impact the lower floors, causing them to
> fall with greater velocity. I wonder what is the cause of
> the increased velocity. Is some force besides gravity acting
> on the impacted floors that would accelerate them at a rate
> faster than the acceleration due to gravity?
> Thank you very much for your time.


> Date: Friday, May 4, 2007 9:53 pm
> Subject: Re: Regarding your WTC collapse hypothesis
> Dear Mr. Bowen: The only driving force is gravity, which
> is clear if you actually read my article. sincerely yours,


> Date: Sat, 05 May 2007 10:40:35 pm
> Subject: Re: Regarding your WTC collapse hypothesis
> Dr. Bazant,
> Thank you very much for your quick response to my question.
> I have read your article and know that gravity is the only
> force pulling the towers down in your argument.
> In your article, you hypothesize that the heat-weakened
> floors collide with lower floors which are not capable of
> carrying the load, causing the lower floors to collapse.
> According to your argument, the collapsegathers mass and
> velocity as it proceeds downward through the entire
> vertical column of the tower.
> My concern is how does the downward velocity increase? In
> other words,if momentum is conserved, how does the
> gravitational force pulling the tower increase? If
> momentum within the tower is not conserved as your argument
> implies and kinetic energy is not dissipated, what is your
> frame of reference with respect to momentum? How is momentum
> conserved?
> Thank you very much for your time and attention.


> Date: Monday, May 7, 2007 10:03 pm
> Subject: Re: Regarding your WTC collapse hypothesis
> Dr. Bowen:
> I think it is perfectly clear if one follows the
> mathematical steps in my paper. Simply stated, the excess
> of the of the gravitational energy loss per story over
> the energy required to crush the story can only go into
> an increase of kinetic energy, and this implies increasing
> velocity.
> Sincerely, ZPB


> Date: Tuesday, May 8
> Subject: Re: Regarding your WTC collapse hypothesis
> Dr. Bazant,
> Thank you so much for your last message.
> Please correct me if I'm wrong, but in your model, the
> gravitational energy of higher floors exceeds the
> gravitational energy of lower floors due to their weakened
> condition by fire.
> If the burning buildings in your model are brought down by
> gravity alone, then the total energy of the collapse must be
> constant because gravity is a conservative force. But gravity
> has always pulled the towers down and that is what is holding
> them to the ground. How does the gravitational force, i.e.
> the acceleration due to gravity, of higher floors exceed the
> weight of the lower floors if the lower floors have the same
> or greater mass?
> It seems to me that in your model either the hotter lower part
> of the building must be slightly buoyed by the fire, and pushed
> upward by the falling force of the colder higher part of the
> building, in accordance with thermodynamics. Or, the total
> energy of the collapse is not closed under gravitation.
> Thank you very much for your time and attention.


> Date: Tuesday, May 8, 2007 2:01 pm
> Subject: Re: Regarding your WTC collapse hypothesis
> Dear Dr. Bowen: I see that you field is mathematics, not
> structural mechanics. Sorry I do not have time for a
> tutorial. If you read my book with Cedolin, it will be
> clear. Sincerely yours, Zdenek Bazant


>Date: Tuesday, May 8, 2007 2:50 pm
>Subject: Re: Regarding your WTC collapse hypothesis
> Dr. Bazant,
> Thank you for your quick response.
> You are correct, my field is mathematics and not structural
> dynamics. But Newton's second law of motion is high school
> physics. The force of gravity is proportional to the distance
> from the center of the Earth. Lower floors of the buildings
> should weigh more, and upper floors should weigh less. How
> do higher floors fall faster than lower floors? What is the
> source of the increased velocity?
> Please take your time to answer my questions; I do not mean
> to intrusive. Thank you for your time and attention.


If any qualified engineers or physicists would like to help me out, I
would be very much obliged.


He got owned

Sounds like you owned him and he tucked tail and ran away man, I'd be surprised if he responded at all at this point. You might also mention the fact that the upper floors having to collide THROUGH each proceeding floor would not cause the rate of fall to increase but would in fact cause the rate of fall to decrease. Thus leaving in question how the tower fell at near free-fall speed.

High School Physics--exactly!

Excellent job!!! Bazant has got to be intentionally obfuscating the truth here--he ain't stupid. There's no other explanation for maintaining such a ridiculous position.


Yes, The less Bazant says the less there is to hang him with. He knows that. Then again, One should not read too much into email strings, for all we know Bazant might have been rushing off to get his toenails painted and couldn't spend the time for proper responses.)

Free Falling Bazant?

Was Bazant suggesting they fell in free fall time? From the post above it sounded like he was only saying that the velocity of the falling mass increased as it fell, although (presumably Bazant would have to say) not as fast as free fall due to the inertia ("gravitational energy loss") of each lower floor which he did indeed admit acted against the downward forces to little avail.

NIST and Dr. Bazant - Simultaneous Failure

NIST and Dr. Bazant - Simultaneous Failure
Gordon Ross, ME

“We're an empire now, and when we act we create our own reality."

Peanut Gallery

I hate playing devil's advocate here but (from my perspective in the peanut gallery) isn't Bazant saying that:

The momentum of the falling mass far exceeded what was required to overwhelm the inertia of each lower floor, therefore the change in momentum of the accelerating and growing mass is mostly due to these forces:

(1) acceleration due to gravity (i.e. things pick up speed as they fall, a constantly increasing velocity) = added momentum;

(2) the added mass of each subsequently failing floor (increases the significance of the falling mass) = added momentum;

(3) relatively minor decreases in velocity (unnoticeable in videos?) due to the inertia of each floor joining with and therefore removing some of the velocity of the entire (growing) large falling mass at the moment of impact with each floor, (or even less so if we assume the falling mass caused the steel supports to fail in sections of many floors, thereby several floors would have already started to gain downward velocity at the moment of impact by the faster moving upper mass) = subtracted momentum; and presumably,

(4) air resistance = subtracted momentum.

It would be nice to truly understand the math that Bazant and Oneismany are trying to describe with words. But for people, like me who would be months of study away from that kind of understanding, it would be more helpful to see a realistic (iron-clad provably accurate) animation of the expected collapse dynamic.

It would be even better if such an animation could be juxtapositioned -split screen style- against a real video of the "collapse" (controlled demolition) and to have this shown in real time.

The problem with that juxtaposition is that people are familiar with objects falling at free-fall acceleration. So the controlled demolition could look "normal" and the graphic, with the inertia of the floors below slowing the whole thing down, could look manipulated. Unless of course Bazant's explanation is valid and they both fall in virtually the same amount of time. As if, duh.

Very good suggestion

I think it was ningen here who posted a link, yesterday I believe, with programming code and mathmatics too, for modeling the collapses.

It was in a paper at j911. Oddly, I can't locate that paper at the site, today at least. The paper demonstrated that, using almost any reasonable assumptions, the progressive collapse would have taken much longer than it actually did -- by several factors.

I hope someone does this graphical depiction, as you say. The code provided in the mathmatician's paper would work, as code for modeling it by graphics. You could even tinker with the assumed parameters, and see how it changes things.



True, but why are you shouting

True, but why are you shouting

There is also a significant difference between `weight`, mass and momentum or kinetic energy and free fall speeds vs acceleration due to gravity and terminal velocity and etc.

It's still there in the Letter's section

Ningen, Romill

Good for you, Ningen. I saw that you posted this yesterday.

Romill, are you still consulting this blog thread? You aren't into computer graphics? If you are, or know someone who is, the letter that Ningen links to above has a very clear programming sequence for modeling the collapses.

Inquiring minds want to know!

I agree with Romill, there are a lot of unanswered questions and I really want to know how this model works out. I am not an expert on structural dynamics, I only know the essentials of physics, but what I know says that there had to be more force than gravity to push the upper floors through the structure beneath at an increased velocity. The crux of Bazant's argument is the increased velocity. But that is saying that something in free fall can "fall faster" with added mass, which is clearly preposterous, if you understand Newton's laws of motion.

There is also this paper you might look at:
"NIST and DR. Bazant - a Simultaneous Failure"

Under gravity alone, nothing can fall faster than free fall speed without resistance from below. The World Trace Center collapsed at free fall speed with resistance from below. Therefore it did not fall due to gravity alone.

How the layperson is confused…

How the layperson is confused…

"The World Trace Center collapsed at free fall speed with resistance from below. Therefore it did not fall due to gravity alone.”

That statement is a strong argument for 911 Truth that is not disputable. HOWEVER are the assumptions that the towers actually collapsed at near free-fall speed correct?

Have the collapse times been measured correctly? For example, looking at a video of the North Tower it is hard to tell when the collapse ended due to all the dust, but it seems to take about 10 to 18 seconds (Starting at the 3:38 point in the clip and ending at about 3:58 when the last object outside dust cloud hits the ground or ending at about 4:06 if you take the point when the heavy dusty debris in the centre seems to reach the ground and the spire of remaining steel shakes from the impact at its base just before it collapses too).

That lines up with statements at , and the final two paragraphs of that “proof” are very powerful in an editorial (if perhaps not a scientific) way: “If air resistance is able to increase total collapse times by even 20 percent, then shouldn't the addition of the resistance of the buildings themselves increase the time several thousand percent, to at least tens of minutes?
Of course the idea of a collapse lasting minutes is absurd. So is the idea of a steel frame building crushing itself.” Exactly.

HOWEVER, there are potential challenges to making the “falling at free fall speed” statement. Take a close look at this video freeze frame at the 3:45 minute mark. Here we see an object falling on the right hand side that was ejected laterally at about the 3:41 minute mark. Except that in that 4 second span of time it has fallen approximately 15 to 20 stories further than the collapsing floors within the building footprint. That tells me that there was at least some resistance from the lower floors. (This is a powerful argument for a debunker who takes issue with an unqualified “collapsed at free-fall speed” statement, but not powerful enough to convince me that the lower floors should have provided even more resistance than this video shows.)

Then there is this from “Taking a Closer Look: Hard Science and the Collapse of the World Trade Center” by Dave Heller at :
“The height of the South Tower is 1362 feet. I calculated that from that height, freefall in a vacuum (read, absolutely no resistance on earth) is 9.2 seconds. According to testimony provided to the 9-11 Commission, the tower fell in 10 seconds. Other data shows it took closer to 14 seconds. So the towers fell within 0.8-4.8 seconds of freefall in a vacuum. Just like WTC7, this speed seemed impossible if each of the 110 floors had to fail individually.”

What does he mean “seemed impossible”? That is not a convincing statement. A convincing statement would have been “was impossible”! “Seemed impossible” is a nice opinion and on face value it seems convincing, but it is NOT science and statements like that can be torn apart by critics.

I am also not convinced by the analysis that Stephen Jones provides for the free fall speeds on pages 27 and 28 of “Why Indeed Did the WTC Buildings Completely Collapse?” at :

Why it is not convincing is that we have Bazant arguing that the energy (mass x velocity) of the falling upper section (what’s that, 47 floors of steel and concrete mass accelerating at 9.8 m/s2 through 2 stories or roughly 30 feet?), an incredibly huge force, totally overwhelming the resistance of the next floor (what’s that, a mass at rest that is but a tiny fraction, i.e. 1/47th, of the mass of the falling upper section plus the resistance of the supporting structure which is presumably not designed to effectively slow the descent of a massive 47 floor section falling upon it from a height of 30 feet?) and therefore, Bazant seems to argue, the fall is virtually unimpeded. Bazant goes on to say that the mass at the next point of impact has increased to 48 floors, so the downward force only grows as its mass increases and its velocity increases at 9.8m/s/s during each fall of 15 feet at which time there is a negligible (?) delay caused by striking the RELATIVELY tiny resistance of each lower floor). That sounds intuitively convincing, so THANK YOU for the link to the paper which thoroughly destroys the Bazant theory, i.e. . (Note to self, do not always believe intuitively convincing arguments.)

For the purpose of dissecting the initial attractiveness of Bazant`s theory to the layperson (like myself), and the theory`s failings, consider the following analogy. Imagine your arm is the supporting steel structure for a floor. Imagine you can comfortably hold a gallon of water over the railing of your apartment building balcony (in your upturned hand with your elbow resting on the railing and your hand cantilevered over the edge of railing). Now imagine that someone takes that gallon of water and drops it from two balconies above onto your outstretched hand and the force breaks your arm off. That seems to be the basic of his argument, but the failing of the analogy (and therefore the failing of Bazant’s theory) is that it is oversimplified (e.g. there are no supporting arms below holding up your arm, etc.), and this simple analogy is a stupid attempt to explain the complex pattern of a building collapse.

By the way, I think that 90% of what Stephen Jones presents is very convincing analysis, such as that starting in the last paragraph of p. 28 and on to p. 29 (of his paper at )
“We observe that approximately 30 upper floors begin to rotate as a block, to the south and east.
They begin to topple over, not fall straight down. The torque due to gravity on this block is
enormous, as is its angular momentum. But then – and this I’m still puzzling over – this block
turned mostly to powder in mid-air! How can we understand this strange behavior, without
explosives? Remarkable, amazing – and demanding scrutiny since the US government-funded
reports failed to analyze this phenomenon. But, of course, the Final NIST 9-11 report “does not
actually include the structural behavior of the tower after the conditions for collapse
initiation were reached.” (NIST, 2005, p. 80, fn. 12; emphasis added.)
Indeed, if we seek the truth of the matter, we must NOT ignore the data to be observed
during the actual collapses of the towers, as the NIST team admits they did. But why did they
follow such a non-scientific procedure as to ignore highly-relevant data? The business smacks of
political constraints on what was supposed to be an “open and thorough” investigation. (See
Mooney, 2005.)”

Free Falling Dust!

The thing is, as has been commented upon many times before, the towers turn into dust before any sort of progressive collapse or pancake collapse can take place. You can't have it both ways: a million tons of dust AND a collapsing building! Let us ask not therefore how the Twin Towers collapsed, but how they were OBLITERATED. Because that is what happened. Forget calculating how long it took the whole building to fall, some small percentage of it probably never reached the Earth's surface and is still trailing off into space behind the planet along with all of the near-earth asteroids. Huge chunks of the towers were flown across the street, and human bone fragments were found on rooftops five years later! None of this fits the description of "collapse."


A respected coworker and I watched the collapses on 9/11/2001 together and he turned to me and said "Those buildings didn't fall, they were blown up." I agreed, and it's haunted me ever since.

I never could understand how anyone watching the explosions can say that the buildings fell in upon themselves due to structural failure. I think people who say that do so because they think "structural failure" are big words that make them sound intelligent.