gedanken

/g*-dahn'kn/ Ungrounded; impractical; not well-thought-out;

untried; untested.

"Gedanken" is a German word for "thought". A thought

experiment is one you carry out in your head. In physics, the

term "gedanken experiment" is used to refer to an experiment

that is impractical to carry out, but useful to consider

because it can be reasoned about theoretically. (A classic

gedanken experiment of relativity theory involves thinking

about a man in an elevator accelerating through space.)

Gedanken experiments are very useful in physics, but must be

used with care. It's too easy to idealise away some important

aspect of the real world in constructing the "apparatus".

Among hackers, accordingly, the word has a pejorative

connotation. It is typically used of a project, especially

one in artificial intelligence research, that is written up in

grand detail (typically as a Ph.D. thesis) without ever being

implemented to any great extent. Such a project is usually

perpetrated by people who aren't very good hackers or find

programming distasteful or are just in a hurry. A "gedanken

thesis" is usually marked by an obvious lack of intuition

about what is programmable and what is not, and about what

does and does not constitute a clear specification of an

algorithm. See also AI-complete, DWIM.