hey thanks for the links i will check them out when i get time and of course i could refer you to other studies were they claim there was not enough potential energy.
No problem. If you want to link to rebuttals to Greening's work, you can go ahead. I've seen some of them already; others here have as well, but it wouldn't hurt at all to replicate the links. And some might welcome it, so that they'll be saved from having to do a search. Anyway, I'll let the engineering types here - rwguinn, R. Mackey, et. all (forgive me for missing anyone else who's commented on this topic) - handle that. Short and to the point, there are some flaws in others works, Ross's in particular, that make the claim about not enough PE being available.
conceptually i just cant imagine it. allow me, if you would, present a simple metaphor. imagine you have a spinal columns supported to remain in a vertical upright position and you drop the head. now conceptually what you are saying is that because the head is basically heavier than the first vertical column then that will be crushed then because the head is heavier than the second vertical column then that too will be crushed...and so on and so forth until there is nothing left not even then head.
or imagine a fly lands on top of a pin, vertically upright in a pin cushion. because the fly (1g) has enough potential energy to crush the first few molecules (.001g) then this process will continue until you have no pin left.
the vertical spin or the pin are designed to support the head or the fly, as was the 90+ floors of vertical columns designed to support the upper 20 floor portion.
the resistance of the first vertical column derives from ALL the vertical columns below.
Due respect, you're making several mistakes there. I think I may need some of the engineering types whom I keep invoking to word the arguments better, but as I understand them, 1. There's a scaling issue, as a totally homogenous structure like a pin, or even a far less homogenous one such as a spine wouldn't react to stress from the upper level in the same way as the lower segments of the Twin Towers do. And 2. A head is not a static load, and the dynamic load of a fly landing on a pin is insignificant compared to the load the segments above the impact zones imposed on the lower sections when the collapse started.
how you can make this argument against the possibility that explosives were implanted is surprising. let me respond in kind the extreme requirememts of a terrorist attack as grand as 911 includes an amazing coordination of opportunity, expertise, and knowledge.
i find it difficult to believe in the extreme that some muslim in a cave could have organised the 911 attacks given the reasons you have just outlined.
indeed if we are to remove the most extreme hypothesis through occam's razor then the "terrorist plotting in a cave" hypothesis over "the planting liquid explosives" should be the one to go, in my opinion.
Again, with all due respect, that's a stretch. First of all, the terrorists were hardly "in caves"; that implies the planners as well as the hijackers were from some paleolithic culture, and had an educational level equivalent to that. That couldn't be farther from the truth. Khalid Sheikh Mohammed, the principle planner, had been living in Kuwait and Pakistan, and had a degree in mechanical engineering. Bin Laden had attended college in either economics, business, or civil engineering (multiple sources disagree on specifics, but agree that he had indeed at least started along a higher-education path. Hani Hanjour (an oft mentioned participant, given all the posts regarding his flight) attended university in Germany and was living in the states, and not in some cave. You'll see that all the participants were hardly "living in caves".
Plus, you're not outlining why the terrorist attack scenario imposed extreme requirements. Purchasing tickets, attacking people with knives, boxcutters, and other weapons, etc. are hardly extreme requirements. So the question stands: What coordination of opporunity, expertise, and knowledge to execute the "terrorist scenario" would be necessary? The pilot training would be one that could be a small difficulty, but there's much evidence to show that some participants did indeed manage to obtain some. What coordination of opportunity was required besides obtaining tickets for flights on the same day? That's hardly an extreme act; it's merely an act of selecting a specific time during the purchase. What coordination of opportunity, expertise, and knowledge was involved in overcoming what little resistance exists on a commercial flight? Back then, it's not like people were told to actively resist.
It is of course your perogative to claim that the "terrorist attack" scenario imposed extreme requirements, but it would help if you would identify what those requirements are. Frankly, I don't see them. Whereas the extreme requirements imposed upon the demolitions scenario have been listed many times over in this forum (but to repeat a subset of them: How to install explosives and not change the collapse initiation point, how to actually install the explosives (liquid or not), when would plotters have the opportunity to install such explosives, and so on, and so forth).
Again, the hijack scenario is the most likely one requiring the least amount of extraordinary occurances. Remember: Flights had been hijacked before, and if anything, the problem was that passenger and air crews had been habituated into giving in, not resisting (no hijacking had resulted in a suicide flight before). All the other events to get the hijackers in place and prepared for the hijackings were hardly unlikely confluences of events, opportunity, and knowledge. They were, in fact, mundane occurances: Enter the country on student or visitors visas, get pilot training, purchase knives, obtain airplane tickets, etc. But the explosives scenario... well, I've stated the problems over and over, and so have others in this forum. Frankly, none of the events in a demolitions scenario are mundane or expected. That's why I called them "extreme" and "extraordinary".
I'm rambling. I'll let others also respond to this. But in summary, it would help to have some elucidation on what makes the "terrorist scenario" so complex and unusual.
Thank you.