"Controlled demolition" of the WTC may have been more than mere explosives.  The 9/11 community of skeptics is deeply divided on this issue, many refusing to entertain the possibility that highly advanced technology may have been used to bring down the towers.  Of note is the degree of pulverization: The rubble was composed of a tremendous amount of ash and dust, with particles less than a micron in size.  Dr. Judy Wood, an expert in mechanical engineering and materials engineering science, posits that some form of "directed energy" was used on the towers, as evidenced by the way they burst into powder from top to bottom.  See her work at http://www.drjudywood.com/ or read about her most recent study here, authored with John Hutchison, a Canadian experimental scientist known for examining radio frequencies and electrostatic energy.

Why are skeptics skeptical of the directed-energy theory?  "Keep it simple" is the reason most often given: It's already hard enough to convince Joe Public that 9/11 was an event carefully orchestrated by insiders (not Arab hijackers), and the buildings didn't come down because they were poorly designed.  Tell Joe Public that "frequencies" were used, and you'll lose him instantly.  Although those who favor limiting the proof to controlled demolition tend to agree that the CD techniques used were likely advanced (see Professor Steven Jones' work on high-temperature accelerants at http://www.stj911.org/), it seems that the two bodies of research lean toward excluding one another.  However, perhaps they simply inhabit two ends of the same spectrum:  Dr. Jones examining a universe of findings in his samples of WTC dust, and Dr. Wood cataloguing thousands of photographs and data of the wreckage in the days and months that ensued -- literally looking up and around into the atmosphere to understand what transpired and how.

AND FROM GEOSCIENTIST LEUREN MORET:  "By investigating the energy budget required to "disappear" two tall buildings as they collapsed, we will find the answer to what happened on 9/11.  Until the energy budget is addressed -- in other words: What does it take to turn two tall buildings into nanoparticles? -- the discussion will never produce any answers that include the sophisticated and exotic energy technologies now available for "special projects."  I am a Livermore Lab whistleblower.  I watched directed-energy experiments being conducted in the atmosphere by the Livermore nuclear weapons lab. Until space-weapons capabilities and HAARP are taken into consideration to explain the molecular dissociation (into nanoparticles) of two very large buildings, as well as the fourth-generation nukes that were used to break down the structural integrity of the buildings, the answers are coming from a noisy room of opinions.

"The investigation must begin with solid science.  No one has explained the presence of levels of uranium, tritium, and the presence of deuterium detected at the WTC in the air-monitoring conducted and reported by Dr. Thomas Cahill for five months after 9/11 (beginning 10/5/01) -- all fingerprints of nuclear devices.  Dr. Cahill reported the highest concentration of metals and nanoparticles ever measured in US air samples.  The event that created this would have required a very high energy budget.  And why did the Department of Energy ask Dr. Cahill to voluntarily do air monitoring specifically AFTER October 5th, and why did DOE want that air-monitoring conducted for five months?  What we know from the Israeli bombing of Lebanon with 5000 US depleted uranium bunker busters is that the bomb craters also had deuterium and high levels of U235 present, as well as very high radiation reported for the first three weeks, which dropped off quickly because these were neutron-activation products.  This is the chemical fingerprint of cold fusion and/or exotic fourth-generation nukes."

Google "Leuren Moret" and read a Finnish expert's nuclear-energy analysis of 9/11 here.