Physics, Bitcoin, Programming, Thermodynamics, Mathematics.
https://www.movable-type.co.uk/scripts/sha256.html In simple terms, bitcoin is considered mined when a solution is found. It is a 64 character string, and with 36 possible inputs per character. The 26 letters of the alphabet and the 10 numerical digits. So that is 36⁶⁴ inputs. The following website