I got to have dinner last night with Robin Hanson, who blogs at Overcoming Bias. Robin is a creative big-picture thinker, who took a twisting career path from physics through philosophy of science and artificial intelligence research to become a tenured professor of economics. He posed a question, which he just re-posed at his blog: what is the most surprising thing we've learned about the universe? Obviously the right answer depends on a set of expectations; surprising to whom? I originally suggested quantum mechanics, and in particular the fact that the outcomes of experiments are not perfectly predictable even in principle. I think that was the most surprising thing to the people who actually discovered it, in the context of what they thought they understood. But what about the most surprising thing to our pre-scientific hunter-gather ancestors? I suggested the fact that the same set of rules govern living beings and inanimate matter, but if you have any better ideas feel free to chime in. But we can ask the complementary question: what is the most surprising thing about the universe that we haven't yet discovered, but plausibly could? Something that is not already reasonably excluded by experiments that we've done, but also wouldn't be readily accommodated by a theoretical model. So "string theory is right" certainly wouldn't count, but neither would "the proton is heavier than the neutron." I once discussed this with Bill Wimsatt on an episode of Odyssey (RealPlayer). I went with "reproducible violations of the Second Law of Thermodynamics." But there are plenty of other good possibilities; what if we discovered tachyons, or that there really was an Intelligent Designer? Suggestions welcome.