An imaginary thought-experiment temporal telephone ("chronophone" for short) which would let Archimedes, in the past, obtain advice from the 21st century. However, it cannot transmit information that is "too anachronistic"; it avoids this by transmitting cognitive strategies instead of words.

You cannot suggest, for example, that women should have the vote. Maybe you could persuade Archimedes of Syracuse of the issue, and maybe not; but it is a moot point, the chronophone will not transmit the advice. Or rather, it will transmit the advice, but it will come out as: "Install a tyrant of great personal virtue, such as Hiero II, under whose rule Syracuse experienced fifty years of peace and prosperity."

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