[porphyra]

He didn't advise Mao directly. He published his "rough estimate" in China Youth Daily on June 16, 1958 as 《粮食亩产量会有多少？》. It's possible, though unconfirmed, that Mao (or his secretary) read this article and was influenced. But yeah, the math was bad and off by an order of magnitude. Even geniuses can't be right all the time and I guess he was quite irresponsible for publishing a hand-wavy back-of-the-envelope estimate like that.

[bwv848]

Qian gave a talk about agriculture at the 6th Supreme State Conference in 1956, Mao directly talked to Qian about his article in 1958 '你在青年报上写的那篇文章我看了，陆定一同志很热心，到处帮你介绍。你在那个时候敢于说四万斤的数字，不错啊。你是学力学的，学力学而谈农业，你又是个农学家。', while later Qian admitted it was theoretically only and he miscalculated, he probably did it out of modesty and he didn't say shit about his impact on tens of millions of death whatsoever. In fact, Mao's secretary at the time was Li Rui, who was a pragmatist and quite liberal during his lifetime. He questioned Mao's sanity, and Mao just blamed Qian.

[porphyra]

Thanks for the correction. That sucks then. Dude should have stayed in his lane making rockets instead of commenting on agriculture.

[defen]

It's a compelling example of the common phenomenon where a certified genius in one field makes a blunder by attempting to reason from first principles to analyze a problem in another field. Not that such things never work; there are success stories too, but it's not guaranteed.