~50 years, from the publishing of Mises' Socialism until...whenever people just gave up in 70s....
Yes, flat earth comparison too strong. Many brilliant economists of the 20th century made great strides in economics working on this question. And frankly is much easier to prove earth round than markets > central planning.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.