You've probably heard that we're in the midst of an A.I. revolution. We're told that machine intelligence is progressing at an astounding rate, powered by "deep learning" algorithms that use huge amounts of data to train complicated programs known as "neural networks." Today's A.I. programs can recognize faces and transcribe spoken sentences. We have programs that can spot subtle financial fraud, find relevant web pages in response to ambiguous queries, map the best driving route to almost any destination, beat human grandmasters at chess and Go, and translate between hundreds of languages. What's more, we've been promised that self-driving cars, automated cancer diagnoses, housecleaning robots and even automated scientific discovery are on the verge of becoming mainstream.