It should be noted that some cranks are to be found inside academia, cranking out papers which are seemingly respectable but are nevertheless (but not always) widely ignored.

Also a person can produce useful, respected work in one field and be a crank in another. Some regard Roger Penrose this way. It is even possible to flip between crank and non-crank in one field: Linus Pauling is a good example.

A number of topics have attracted the interest of large numbers of cranks, including:

• squaring the circle
• disproving Einstein's theory of relativity
• disproving quantum mechanics
• producing unified Theories of Everything
• various conspiracy theories
• lossless data compression of random data
• finding a simple proof to Fermat's last theorem
• cures for cancer

The main distinguishing factor between kooks and quacks, frauds and hoaxers is that kooks genuinely believe that their perceptions and experiences constitute a valid model of reality. Predictably, "kooks" tend to draw criticism and generate controversy; it has been speculated that some kooks are motivated by a desire for such attention.

The kook trademark is paranoia and grandiosity. Kooks will often build up elaborate imaginary support structures, fake corporations and the like, and continue to act as if those things are real even after their falsity has been documented in public.

While they may appear harmless, and are usually filtered out by the other regular participants in a newsgroup or mailing list, they can still cause problems because the necessity for these measures is not immediately apparent to newcomers; there are several instances on record, for example, of journalists writing stories with quotes from kooks who caught them unaware.

See also

• Delusion
• Quackery
• Conspiracy theory