Applied to a person, the term crank refers to someone who (usually) wrongly believes or (sometimes) pretends to have knowledge of some subject and writes or speaks in an authoritative fashion about it. Such a person is a source of amusement and/or annoyance to actual experts.
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
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.