Why 9/11 conspiracy theories persist 25 years later

Twenty-five years after the morning of September 11, 2001, when al-Qaeda hijacked four commercial airplanes and killed nearly 3,000 people in coordinated attacks on New York and Washington, the event remains the subject of elaborate conspiracy theories. Two planes struck the World Trade Center towers in Manhattan. A third hit the Pentagon. The fourth, United Airlines Flight 93, crashed in rural Pennsylvania after passengers and crew members fought back against the hijackers, likely preventing an attack on the Capitol. The attacks were broadcast live to the world. They changed how nations think about security, terrorism, and themselves. Yet despite decades of investigation, despite the work of the National Institute of Standards and Technology, MIT, and independent engineering firms all reaching identical conclusions about what happened and why the towers fell, a significant portion of the American public remains unconvinced by the official account.

According to a 2023 YouGov survey, one in five Americans believe their own government orchestrated the attacks. The most persistent alternative narrative centers on controlled demolition—the claim that explosives, not the impact of the planes and the resulting fires, brought down the twin towers. Proponents point to horizontal clouds of smoke visible during the collapses as evidence of detonations in lower floors. No explosives were ever found at the site. No credible evidence supports the theory. Yet it circulates constantly on social media, shared by millions, reinforced by a small number of scientists whose arguments have been systematically refuted by mainstream engineering analysis. The theory persists not because new evidence has emerged, but because it answers a psychological need.

Daniel Jolley, a social psychologist at the University of Nottingham who studies how conspiracy theories take root in societies, explains that traumatic, sudden events like 9/11 create gaps in our understanding. People want to feel in control. They want certainty. They want the anxiety to stop. When official explanations feel incomplete or when institutions have lost public trust, conspiracy narratives rush in to fill the void. They offer a coherent story, even if that story is false. An anxious person, someone whose life experience has taught them to distrust authority, is more vulnerable to these narratives. But Jolley emphasizes that belief in conspiracy theories is not a sudden rupture. It is a journey, often rooted in accumulated grievances and the way a person has learned to process crisis.

Social media has become the primary vehicle for spreading these theories. Facebook launched in 2004, three years after 9/11. Instagram, WhatsApp, Telegram, and YouTube followed, each reaching billions of users. These platforms make it easy to move from one piece of content to another, to descend what Jolley calls "a rabbit hole"—clicking deeper and deeper into a subject until the person has consumed hours of material, much of it false, all of it reinforcing the same basic narrative. The platforms do not always move quickly to remove misinformation. The false claims become part of everyday content, normalized, woven into the fabric of what people encounter on their phones.

One particularly troubling dimension of 9/11 conspiracy theories involves antisemitism. The false claim that Jewish people orchestrated the attacks has been widely shared on social media. This narrative draws on an ancient antisemitic trope: the idea that Jews secretly control world events and seek global domination. There is no evidence for this claim. Yet it persists, and it has real consequences. Jolley notes that certain groups—Jews, Muslims, LGBTQ+ people—are historically blamed for crimes they did not commit. In 2019, a right-wing extremist in Halle, Germany, who had been consuming antisemitic conspiracy theories online, attempted to storm a synagogue and killed two people at a nearby kebab shop.

Karen Douglas, a social psychologist at the University of Kent, states plainly: "Anyone can fall into conspiracy theories if the circumstances are right." The theories are dangerous for three reasons. First, they promise to reduce anxiety but typically increase it, deepening mistrust of government and other people, leading to social isolation. Second, they mix fact with falsehood in ways that cannot be easily disproven, because their core claim is that powerful actors are hiding the truth. Third, they have consequences. Conspiracy theories have been linked historically to prejudice, genocide, risky health behavior, climate denial, and more recently to the QAnon movement and COVID-19 misinformation that influenced how people acted during a pandemic.

In Germany, organizations like the Amadeu Antonio Foundation and the Federal Agency for Civic Education offer guidance on how to respond when friends or family members embrace conspiracy narratives. The advice is straightforward: communicate as equals, research together to find reliable information, call out antisemitism and racism clearly, and make your opposition to extreme positions known. The historian Claus Oberhauser emphasizes that societies need to rebuild trust in facts and science. This is not a technical problem with a technical solution. It is a question of how people relate to institutions, to each other, and to the possibility of shared truth. A quarter-century after the attacks, that work remains unfinished.