9/11 Truth Movement

Claim: The September 11, 2001 attacks were either allowed to happen on purpose ("LIHOP" – let it happen on purpose) or actively orchestrated ("MIHOP" – made it happen on purpose) by elements of the U.S. government, often citing the collapse of World Trade Center Building 7 as evidence of "controlled demolition."

Origins: Emerged within months of the attacks, spread rapidly via early internet forums and the 2005 documentary Loose Change.

Why it's false: Multiple independent engineering investigations — most notably by the National Institute of Standards and Technology (NIST) — found that fires weakened structural steel, causing progressive collapse consistent with known physics, not demolition. No physical or testimonial evidence of explosives has ever been found, and the number of people (thousands of engineers, officials, and journalists) who would need to stay silent makes the scale of alleged conspiracy implausible.

Status: Rejected by the engineering and scientific consensus, though pockets of the theory persist, especially online.