Suppose you traveled back in time—say 40,000 years into the past—and then you got stuck. What would you do? How would you rebuild all the stuff that you like? That's the premise of the book How to Invent Everything: A Survival Guide for the Stranded Time Traveler, by Ryan North. Without getting into the nitty-gritty details, it gives you the general idea of how things like an electric motor or wifi work.

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