A person who believes the theory of relativity in physics is wrong or that he/she has a proof of Fermat's Last Theorem that uses nothing more than high school math is called a "crank" or "crackpot" in English. Is there a word for such people in Russian? I searched around and found чудак, but a native speaker I asked didn't think that was an accurate word for such people and also didn't know of a good translation.
Quite often a word фрик (borrowed from English freak) is used in this context. In Russian it has the meaning of crank in scientific context.
You can also use the word "опровергатель" ("refuter") which can convey negative meaning.
There is a wider term for promoting pseudoscientific practices - шарлатанство (quackery). All people who don't believe in relativity (and have an alternative theory), know how to prove Fermat's Last Theorem using only sophomoric algebra - all these people are definitely
шарлатаны. It's just that this term includes not only enthusiastic half-educated amateurs, who believe that their contributions are important, but malicious, deliberate rogues as well. For example, one who sells fake drugs as if it is an efficient cure is definitely a
As for the precise equivalent, I hardly can name one, though there are some candidates. In Russian word
любитель (amateur) in some context has quite strong negative connotations and is used for indicating exactly those who claim to prove something wrong, but his proof is flagrantly unscientific. For example, this well known speech of the Russian linguist Andrey Zaliznyak is titled "О профессиональной и любительской лингвистике" ("On professional and amateur linguistics").
A person who just denies the achievements of modern science can be called
мракобес, but this is, once again, somewhat wider. For example, those who deny evolution, is, most probably
мракобес, but in some cases
мракобес (as well as
ретроград) is about a fanatic person who hates any kind of scientific progress at all.
Finally, it's worth mentioning that among mathematicians there existed a special term for monomaniac provers of Fermat's Last Theorem:
ферматист (check out this article). I've tried to recall something similar about relativist deniers, but, again, have some doubts that there exists something more universal than just
This is a separate part and a separate answer which I would not like to be confused with the previous one. This ones deals exclusively with quantitative groups description strategies.
When referring to specific pseudo-sciences/quasi-theories, Russian speakers also use productive models derived from personal names of 'founders' referring to their followers, e.g. лысенковцы, фоменковцы, княжениты.