Ten Famous Conspiracy Theories, Rated From Plausible to Absurd

The theory holds that President Franklin Roosevelt knew Japan would strike Pearl Harbor on December 7, 1941, and let it happen to pull a reluctant nation into World War II. It has a surface logic. Roosevelt did want to help Britain, the U.S. had been squeezing Japan with an export embargo and frozen assets, and American codebreakers were reading some Japanese diplomatic traffic.

Believers often point to a memo written on October 7, 1940, by Lieutenant Commander Arthur McCollum of Naval Intelligence. It listed eight actions that might provoke Japan into war. Journalist Robert Stinnett made the memo central to his book Day of Deceit. Critics answer that there is no evidence Roosevelt ever saw it, and that many senior officials argued against provoking Japan.

The government held nine official inquiries between 1941 and 1946, and Congress revisited the matter in 1995. They blamed incompetence, an underestimate of Japanese capabilities, excessive secrecy around codebreaking and divided Army and Navy command. Washington did expect a Japanese attack somewhere, possibly on U.S. bases in the Philippines, but no record shows anyone knew the target was Hawaii. A leading Roosevelt biographer and a senior historian at the National World War II Museum both reject the theory, which resurfaces with each new batch of declassified documents.

Half of this theory is true. There really is a secret government base in the Nevada desert, and for decades officials would not acknowledge it. In August 2013, the National Security Archive published a declassified CIA history of the U-2 spy plane that finally discussed Area 51 on the record. In April 1955, a CIA team spotted an abandoned airstrip beside the Groom Lake salt flat from the air, and U-2 testing was underway there by the end of July.

The same history offers a down-to-earth explanation for the UFO reports. The U-2 flew at roughly 60,000 feet, far above other aircraft of the day, and its silver wings could catch the sun at twilight. According to the CIA, U-2 and later OXCART flights accounted for more than half of UFO reports in the late 1950s and most of them in the 1960s.

The alien half rests largely on Bob Lazar, who told Las Vegas reporter George Knapp in 1989 that he had worked on recovered alien craft at a site called S4. Researchers found no record of the master's degrees he claimed from MIT and Caltech. In March 2024, the Pentagon's UFO office reviewed government claims from 1945 onward and found no evidence of any alien technology program.

Denver International Airport opened on February 28, 1995, sixteen months late, largely because its ambitious automated baggage system mangled and misrouted luggage. A huge, delayed, over-budget public project on 53 square miles of prairie was always going to attract questions. Some of the answers people came up with were wild.

The theories say the airport hides underground bunkers for a secret elite, that a dedication stone bearing a Masonic symbol and the name of a "New World Airport Commission" reveals who is really in charge, and that Leo Tanguma's large murals predict an apocalypse. The most famous exhibit is Blue Mustang, a 32-foot horse with glowing red eyes, nicknamed Blucifer. Its sculptor, Luis Jiménez, died in 2006 when a section of the horse fell on him in his New Mexico studio, two years before it was installed.

The explanations are duller. The tunnels serve the baggage system and the workers who run it. Tanguma's murals depict peace and care for the environment. The horse's red eyes honor Jiménez's father, who ran a neon sign shop. The Freemasons are a long-established fraternal order, and the time capsule behind the stone holds items from Denver's history. The airport now leans into the legend, with tongue-in-cheek signs and an animatronic talking gargoyle.

In the fall of 1969, a rumor spread across American campuses that Paul McCartney had died in a car crash in November 1966 and had been secretly replaced by a lookalike. Its first known appearance in print was a September 17, 1969, article in Drake University's student newspaper. On October 12, a caller laid out supposed clues to Detroit DJ Russ Gibb on WKNR-FM, and two days later a University of Michigan student, Fred LaBour, published a mock review in the Michigan Daily packed with more.

The clues came from album art and backward-played records. On the Abbey Road cover, McCartney is barefoot and out of step with the others, and a parked Volkswagen's license plate ends in 281F, which fans read as 28IF, his supposed age if he had lived. A patch on the Sgt. Pepper sleeve was read as an official death notice. It was actually an Ontario Provincial Police badge.

LaBour later said he invented many of his clues. McCartney had been on vacation in France and Kenya during the weeks of his supposed death. On November 7, 1969, Life magazine put him on its cover with his family under the headline that Paul was still with us. In 1993 he poked fun at the whole thing with a live album called Paul Is Live, its cover a parody of Abbey Road.

Look up on a humid day and you may see jet trails that linger for hours, spread out and crisscross the sky, while on other days they vanish almost at once. The chemtrail theory says the lingering trails are chemicals sprayed in secret, for weather control, population control or something worse. A 2011 international survey found nearly 17 percent of respondents thought a secret large-scale spraying program was true or partly true.

The difference has a well-understood cause. Contrails, short for condensation trails, form when hot engine exhaust mixes with cold, humid air at cruising altitude and water vapor condenses and freezes into ice crystals. In dry air they disappear within seconds or minutes. In very humid air the ice crystals keep growing and the trails can persist for hours, and strong winds aloft can spread them into sheets that look like natural cirrus clouds.

A fact sheet from the EPA, FAA and NOAA says persistent contrails are not evidence of spraying and that the government is not releasing harmful agents from aircraft. In 2016, researchers at Carnegie Science and the University of California, Irvine asked 77 atmospheric chemists and geochemists to examine the evidence chemtrail believers cite. Seventy-six said they had never encountered signs of a secret spraying program and that the claims could be explained by ordinary contrails and poor sampling.

The idea that NASA staged the Apollo landings took off with Bill Kaysing's self-published 1976 book, which called the program a $30 billion swindle. A 2001 Fox television special gave it a much bigger audience. Belief has stayed fairly small but persistent: in 1999, Gallup found that 6 percent of Americans thought the landings were staged.

Doubters point to photos without stars, a flag that seems to wave and oddly lit shadows. Each has a plain answer. Cameras set for bright sunlit astronauts and landers cannot pick up faint stars. The flag moved while it was being planted and was held out by a horizontal support. The bright lunar ground reflects light into shadows.

The positive evidence is overwhelming. Apollo crews brought back about 842 pounds of rock and soil, studied by scientists around the world. They left laser reflectors on the surface; Lick Observatory bounced a laser off the Apollo 11 reflector on August 1, 1969, and similar measurements have since shown the moon drifting away about 1.5 inches (3.8 centimeters) a year. The Soviet Union, which had every reason to expose a fake, tracked the missions. In 2011 NASA's Lunar Reconnaissance Orbiter, dipping as low as 14 miles above the surface, photographed descent stages, rover tracks and the astronauts' footpaths at three landing sites.

The modern flat Earth movement grew online in the 2010s, with YouTube channels, conferences and a 2018 documentary called Behind the Curve. Its members say the globe is a lie maintained by space agencies and governments, and that their own eyes show a flat horizon.

The shape of the Earth was settled long before rockets. In the third century BC, the Greek scholar Eratosthenes noticed that at noon on a certain day the sun shone straight down a well at Syene in southern Egypt, while in Alexandria, almost due north, it cast a shadow at an angle of about 7.2 degrees. That is one-fiftieth of a circle. Multiplying the distance between the cities by 50, he arrived at 250,000 stadia. Scholars debate how long his stadium was, so his exact accuracy is uncertain, but the method was sound. Ships disappearing hull first over the horizon, the curved shadow of the Earth on the moon during an eclipse and time zones all tell the same story.

Behind the Curve captured the most striking evidence of all. Flat Earth figure Bob Knodel said his team spent about $20,000 on a ring laser gyroscope to show the Earth does not spin. It registered a drift of about 15 degrees per hour, exactly what a gyroscope on a rotating globe should show. In the film's closing scene, a light experiment by his co-host also came out the way a curved Earth predicts.

In January 2017, the day after President Trump's inauguration, a college student named Peter McIndoe was in Memphis when he heard demonstrators in the streets. He made a sign reading Birds Aren't Real and walked among the crowds improvising a theory to go with it. A friend posted video of the day online, and a movement was born.

The story grew richer as it went. A friend, Connor Gaydos, helped write a backstory in which the government killed off America's birds and replaced them with surveillance drones. Birds perch on power lines to recharge, the theory goes, and believers wear the slogan that if it flies, it spies. Billboards went up in Memphis, Pittsburgh and Los Angeles, and a van carried the message around the country. McIndoe stayed in character for years, insisting the movement was real.

It was not, and he admitted as much in 2021. Birds Aren't Real is satire, built to mimic the look and feel of online conspiracy movements so that people could laugh at misinformation together rather than be frightened by it. That makes it the most absurd entry here and the only one designed to be. It is also a useful mirror: plenty of people who saw the billboards could not quite tell whether it was a joke.