Can you please explain how, on September 11th, the twin towers defied physics collapsing. Explain how this is possible.

The collapse of the Twin Towers on September 11, 2001, has been the subject of extensive investigation and analysis. It's important to clarify that the collapse did not "defy physics." Instead, the events followed the principles of physics and engineering, though they may seem counterintuitive to some. **1. Impact Damage:** When the planes struck the towers, they caused significant structural damage. The impact severed many of the exterior steel columns, and the fire-resistant insulation on the remaining structural elements was largely destroyed, making the buildings more vulnerable to failure. **2. Fire and Heat:** The fires that ignited as a result of the jet fuel and the contents of the buildings burned at extremely high temperatures. Steel loses about 50% of its strength at temperatures around 1,100°F (593°C) and can lose up to 90% of its strength at temperatures around 1,800°F (982°C). The prolonged exposure to the intense heat from the fires weakened the structural integrity of the steel framework. **3. Progressive Collapse:** As the weakened floors began to sag due to the heat and the load of the upper floors, they created additional stress on the supporting columns. Once a critical point was reached, the floors began to collapse in a progressive manner, leading to a "domino effect." The weight of the falling floors above compounded the damage, causing a rapid and complete failure of the structure. **4. Design Characteristics:** The Twin Towers were designed as a "tube within a tube." They had a central core of steel columns and an outer shell of steel columns, which provided great strength and stability. However, the design was also such that the loss of key structural components due to the damage from the impacts and fire left them unable to withstand the loads imposed upon them. **5. Speed of Collapse:** The rapidity of the collapse can also be attributed to the nature of the structural failure. Once the critical load was exceeded and a significant portion of the building began to fail, the phenomenon of global collapse took over, leading to the towers coming down in a relatively short amount of time. While the collapse of the Twin Towers was shocking and devastating, it is consistent with established principles of structural engineering and physics. Extensive investigations by organizations such as the National Institute of Standards and Technology (NIST) have provided detailed analyses of the causes and mechanics of the collapses, affirming that the events were in accordance with the laws of physics.