The official conspiracy theory maintains that the World World Trade Center (WTC) Towers collapsed due to fire after being hit by jet airplanes piloted by terrorists. This theory is supported to a certain extent by the National Institute of Standards and Technology (NIST). A massive problem with this theory is that it violates the laws of physics, namely Law of Conservation of Momentum and Law of Conservation of Energy.
Momentum is mass times velocity, p = mv. The total momentum of a closed system cannot change. Although momentum conservation in non-closed systems is not 100% accurate because of resistance forces such as friction and air resistance, the law of conservation of momentum is still extremely good for providing accurate estimates of speed and for analyzing collisions, such as whether a building fell down or was brought down by controlled demolition. This is because the contact forces of collisions are very large compared to any resistance forces. If an object falls onto another object the falling object will have a certain momentum. The velocity of the object will be the acceleration due to gravity or free fall which is approximately 9.81 m/s2. The object will continue at the same velocity unless acted on an outside force. At the point of collision where the two objects hit each other, there will be a transfer of momentum. In the case of the WTC towers the collision involves a failure on one or more floors which causes the upper part of the building to collide with the lower part. This is referred to as an inelastic or viscous collision because the two objects collide and stick together. The viscous behavior refers to the deformation the material undergoes during the collision. Energy is dissipated through molecular motion and heat generation by this deformation. So a considerable amount of momentum will be expended in breaking up the lower part of the building as well as the upper part. During the collision, the two objects exert equal and opposite forces on each other. The force of gravity pulling down the detached part of the building is equal to the force of the Earth pulling the detached building upward. However, due to safety factors the resisting force of the remaining building dwarfs the downward pushing gravitational force . If there were no much stronger resisting force, no building would stay up because they are not counteracting the force of gravity. How could gravity pull the building down when there is a far stronger force resisting the gravitational force? The remaining part of the building is in the way. It is a much stronger force counteracting the weaker gravitational force. That is how buildings stay up so long. The remaining part of the building should at the very least slow the collapse considerably, not provide almost no resistance at all. Also, a huge portion of the building is pulverized into dust and ejected outwards somehow, detracting considerably from the falling mass.
Large building demolitions work by taking out the building supports floor by floor with explosives . This is how they deal with the considerable upward force and how demolished buildings thus can realize free-fall speeds. Even if ordinary office fires could cause massive steel support columns to fail (simultaneously and in just the right perfectly timed sequence) the whole building was not on fire.
Another big problem for the official conspiracy theory is that you have to explain how structural steel and bone fragments were ejected at high speed onto neighboring buildings. Large multi-ton pieces of steel were ejected horizontally up to 600 feet and embedded into buildings . You also have to explain how most of the concrete and office contents were reduced to an ultra-fine dust . A gravity collapse simply does not have the massive energy required to perform these feats. If a building free falls there is no energy left to pulverize concrete to dust or embed structural steel into buildings up to 600 feet away . In other words the official conspiracy theory also violates the law of conservation of energy. All these anomalies are explained and the laws of physics are not violated if the buildings were brought down using explosives.
The laws of physics have never been violated. So if you propose a theory that requires violating the laws of physics you have a huge problem. Scientists would at best completely ignore such a theory but usually proponents of such theories are ridiculed mercilessly, unless of course it seems, if you are the US government. In science one observation that disagrees with the predictions of a theory means the theory is wrong. The official story regarding the 9/11 WTC tower collapses clearly violates two fundamental laws of physics. The theory that the WTC towers were brought down by controlled demolition on the other hand does not violate the laws of physics. So which theory does science dictate we reject?
 S. Sunder, W. Grosshandler, H. S. Lew, et al. “National Institute of Standards and Technology (NIST) federal building and fire safety investigation of the World Trade Center disaster, answers to frequently asked questions”, Gaithersburg, MD: National Institute of Standards and Technology, August 30, 2006. [Online]. Available: NIST, http://wtc.nist.gov.
 Steven E. Jones, Frank M. Legge, Kevin R. Ryan, Anthony F. Szamboti, James R. Gourley, “Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction”, The Open Civil Engineering Journal, Volume 2, 2008
 Griffin, David Ray (2004). The New Pearl Harbor: Disturbing Questions about the Bush Administration and 9/11, Northampton, Massachusetts: Interlink. chapter 2.
 Gordon Ross, ME, “NIST and Dr. Bazant – Simultaneous Failure”, Journal of 9/11 Studies, Volume 11 – May 2007
 Dr. Steven E. Jones, “Why Indeed Did the World Trade Center Buildings Completely Collapse?”, Journal of 9/11 Studies, Volume 3 – September 2006
http://www.journalof911studies.com/volume/200609/Why_Indeed_Did_the_WTC_Buildings_Completely_Collapse_Jones_Thermite_World_Trade_Center.pdf (section 9)
 Harris, Tom (2000). “How Building Implosions Work,” available at:
http://science.howstuffworks.com/building-implosion.htm, ca. 2000.
 Dr. Frank Legge, “9/11 – Evidence for Controlled Demolition: a Short List of Observations “, Journal of 9/11 Studies, Volume 1 – June 2006