What does it mean to send "one sentence" to the future? Does the future understand English? How precise of a concept can we give them?
Typically, I interpret that as "what concept would you like people to have instinctually?", which most people respond to with "here's something that I wished my contemporaries understood, and so I'm going to inflict it on imaginary future post-apocalyptic humans," apparently because they haven't suffered enough.
When was the atomic hypothesis confirmed? If I recall correctly, it was only when chemists started noticing that the outputs of chemical reactions tended to factorize a certain way, which is to say that it took millennia after Democritus to get the point where the atomic hypothesis started making clearly relevant experimental predictions.
Mmm. I don't think it's that terrible, but it does appear designed to put people at Alhacen's level on the right track, rather than to put people at Aristotle's level on the right track. For example, I seem to recall the correct understanding of heat being held up by the atomic hypothesis not being widely accepted; if you know that atoms exist, then calculating everything correctly is fairly straightforward- but you do need some math to get it right. Feynman misses the opportunity to hint at electricity except very obliquely.
"Stop trying to sound wise and come up with theories that make precise predictions about things you can measure in numbers."
Why start off with the negative? Galileo's quote seems to capture the same idea more positively:
Measure what is measurable, and make measurable what is not so.
As for macroeconomics, money is useful, but only insofar as it facilitates trade. My first try would be:
Human skill accumulates because of specialization, returns to specialization are capped by the size of the market; trade increases wealth by allowing greater specialization which allows greater skill.
Kleinert disputes the attribution to Galileo, though Galileo did emphasize measurement in other epigrams. You didn't make an argument from authority, but I might like one, to avoid hindsight.
So apparently Richard Feynman once said:
I could be missing something, but this strikes me as a terrible answer.
When was the atomic hypothesis confirmed? If I recall correctly, it was only when chemists started noticing that the outputs of chemical reactions tended to factorize a certain way, which is to say that it took millennia after Democritus to get the point where the atomic hypothesis started making clearly relevant experimental predictions.
How about, "Stop trying to sound wise and come up with theories that make precise predictions about things you can measure in numbers."
I noticed this on Marginal Revolution, so I shall also state my candidate for the one most important sentence about macroeconomics: "You can't eat gold, so figure out how the heck money is relevant to making countries actually produce more or less food." This is a pretty large advance on how kings used to think before economics. I mean, Scott Sumner is usually pretty savvy (so is Richard Feynman btw) but his instruction to try to understand money is likely to fall on deaf ears, if it's just that one sentence. Think about money? Everyone wants more money! Yay, money! Let's build more gold mines! And "In the short run, governments are not households"? Really, Prof. Cowen, that's what you'd pass on to the next generation as they climb up from the radioactive soil?
*Cough.* Okay, I'm done. Does anyone want to take their own shot at doing better than Feynman did for their own discipline?