[W]e all know that arguments from authority carry little weight: what should sway you is not the mere fact of some other person stating their opinion, but the actual arguments and evidence that they’re able to bring. Except that as we’ve seen, for Bayesians with common priors this isn’t true at all! Instead, merely hearing your friend’s opinion serves as a powerful summary of what your friend knows. And if you learn that your rational friend disagrees with you, then even without knowing why, you should take that as seriously as if you discovered a contradiction in your own thought processes. This is related to an even broader point: there’s a normative rule of rationality that you should judge ideas only on their merits—yet if you’re a Bayesian, of course you’re going to take into account where the ideas come from, and how many other people hold them! Likewise, if you’re a Bayesian police officer or a Bayesian airport screener or a Bayesian job interviewer, of course you’re going to profile people by their superficial characteristics, however unfair that might be to individuals—so all those studies proving that people evaluate the same resume differently if you change the name at the top are no great surprise. It seems to me that the tension between these two different views of rationality, the normative and the Bayesian, generates a lot of the most intractable debates of the modern world.
Scott Aaronson, ‘Common Knowledge and Aumann’s Agreement Theorem’, Shtetl-Optimized, August 14, 2015
Quantum Computing since Democritus is a candidate for the weirdest book ever to be published by Cambridge University Press. The strangeness starts with the title, which conspicuously fails to explain what this book is about. Is this another textbook on quantum computing—the fashionable field at the intersection of physics, math, and computer science that’s been promising the world a new kind of computer for two decades, but has yet to build an actual device that can do anything more impressive than factor 21 into 3 × 7 (with high probability)? If so, then what does this book add to the dozens of others that have already mapped out the fundamentals of quantum computing theory? Is the book, instead, a quixotic attempt to connect quantum computing to ancient history? But what does Democritus, the Greek atomist philosopher, really have to do with the book’s content, at least half of which would have been new to scientists of the 1970s, let alone of 300 BC?
Having now read the book, I confess that I’ve had my mind blown, my worldview reshaped, by the author’s truly brilliant, original perspectives on everything from quantum computing (as promised in the title) to Gödel’s and Turing’s theorems to the P versus NP question to the interpretation of quantum mechanics to artificial intelligence to Newcomb’s Paradox to the black hole information loss problem. So, if anyone were perusing this book at a bookstore, or with Amazon’s “Look Inside” feature, I would certainly tell that person to buy a copy immediately. I’d also add that the author is extremely handsome.
Scott Aaronson, Quantum Computing since Democritus, Cambridge, 2013, p. ix