Expert Error consists of serious errors by recognized experts about scientific, engineering or economic theories or possibilities. We start with examples:
- Lord Kelvin claiming heavier than air flight, radio, and radioactivity were impossible.
- Opposition by 19th century European doctors to Ignaz Semmelweiss's discovery that invisible "particles" were transmitting disease and killing patients in a Vienna hospital.
- Albert Einstein thought nuclear power would never be commercially viable.
- Opposition by experts to the United States Patent Office, because supposedly everything useful has been invented.
- Thomas Watson, chairman of IBM in the 1960s, believed there would never be a market for more than a handful of computers in the entire world.
- Irving Fisher, professor of economics at Yale, declared a few days before the 1929 stock market crash, "Stock prices have reached what looks like a permanently high plateau. I do not feel there will be soon if ever a 50 or 60 point break from present levels, such as (bears) have predicted. I expect to see the stock market a good deal higher within a few months."
- Philipp von Jolly, professor for physics and mathematics at the University of Munich, advised Max Planck in 1874 not to study physics as almost everything was already discovered, and all that remained was to fill a few unimportant holes.
- Aristotle had "quaint" notions of physics (such as the idea that force must be continuously applied to keep a body in motion; he had no idea of friction or air resistance). He believed in the spontaneous generation of life from inanimate matter; experts adhered to his theories for over two thousand years.
- Jean Boulliard of the French Academy of Sciences claimed that mechanical reproduction of human speech was an impossibility.
- Sir George Bidell Airy, Astronomer Royal of Great Britain, persuaded the British government to discontinue funding for Charles Babbage's analytical engine on the grounds that it was "worthless." Modern astronomy, of course, relies heavily on computers that wouldn't have been possible without Babbage's work.
- A Yale economics professor dismissed Fred Smith's idea of overnight mail delivery aided by computers as deserving no better than a 'C' grade because "in order to earn better than a 'C,' the idea must be feasible." 
- Steve Jobs and Steve Wozniak's idea for a personal computer was summarily dismissed by Atari and Hewett-Packard, in part because they didn't have college degrees yet.
- Marechal Ferdinand Foch, professor of strategy at Ecole Superieure de Guerre, dismissed airplanes as "interesting toys" of no military value.
- An 1856 publication in a prominent Viennese medical periodical, Viennese Medical Weekly, by Jozsef Fleischer, a student of Semmelweis, showed success of chlorine washings. However, the editor for the periodical wrote at the end of the report “We believe that this chlorine-washing theory has long outlived its usefulness. The experiences and statistical results of most maternity institutions protest against the views presented above. ... The Semmelweiss Reflex
- This opposition can be found in many forms, from weakening the strength of patents by small inventors today to repetition of a quote attributed to Charles Duell, Commissioner of the Patent Office, in 1899: "everything that can be invented has been invented." While Charles Duell never said such a thing and it doesn't reflect his position on patents at all, "this saying has been so often quoted that it has been gradually accepted as a truth, and thus being still repeatedly quoted again and again even by prominent scholars." Bojan Pretnar, "Two Sources of Persistent Patent Controversy," p.4
- Quoted on Oct. 17, 1929.