Back in high school I read this book called The Third Culture which was edited by John Brockman. I picked it up because I'd just read C.P. Snow's book The Two Cultures with which I've been obsessed ever since.
Now I don't believe that the people who wrote essays for Brockman's book represent anything like a third culture. They're science types. They're writing about questions which might be considered philosophy, but scientists have always done that. He edited another one, more recently, called The New Humanists which was exactly the same sort of thing. (I have to admit I didn't finish that one, because I lost it before I'd read all the essays. Andy, I think you've forgotten, but I owe you a book...)
Some time ago I heard that he'd started a web page called "Edge." And now, thanks to Peter Woit's reminder, I'm taking a look at it.
It has a feature in which Brockman asks lots of his famous, science type correspondents, the same provocative question. "What do you believe is true, even though you cannot prove it?"
That's the kind of question that takes a lot of nerve to ask. And it takes serious cajones to answer it honestly, for a scientist.
Richard Dawkins admits that he cannot prove that "All life, all intelligence, all creativity and all 'design' anywhere in the universe, is the direct or indirect product of Darwinian natural selection. It follows that design comes late in the universe, after a period of Darwinian evolution. Design cannot precede evolution and therefore cannot underlie the universe."
Physicist Freeman Dyson takes the cowardly route, and goes with an unprovable mathematical conjecture. (I'd be tempted by this sort of answer too, only I'd pick some geometric axioms.)
Biologist Jared Diamond, author of the scientific explanation of human history called Guns, Germs, and Steel, takes the opportunity to explain a hypothesis he says he can't yet prove, and so does Lynn Margulis, the biologist who came up with the currently accepted theory of the origin of eukaryotic life, and so does Daniel Dennett, author of Consciousness Explained.
Gregory Benford, physicist and science fiction writer, ducks the question, and asks one of his own: why should there be laws of nature? I guess we can take it that he believes, but cannot prove, that these laws are universally true. Clifford Pickover, computer scientist and creator of Clifford A. Pickover's homepage (try his ESP experiment) also tries to dodge, by phrasing his answer with "ifs". "If we believe that consciousness is the result of patterns of neurons in the brain, our thoughts, emotions, and memories could be replicated in moving assemblies of Tinkertoys." Be a man, Cliff. Do you believe Tinkertoy brains could think, or not?
The physicists in general do better at acknowledging how little we can actually prove Leonard Susskind, states the assumption that underlies quantum mechanics and statistical mechanics: "If I were to flip a coin a million times I'd be damn sure I wasn't going to get all heads. I'm not a betting man but I'd be so sure that I'd bet my life or my soul. I'd even go the whole way and bet a year's salary. I'm absolutely certain the laws of large numbers—probability theory—will work and protect me. All of science is based on it. But, I can't prove it and I don't really know why it works." (This reminds me of a story I read in the anthology "Fantasia Mathematica" in which someone gets really upset when a collection of monkeys at typewriters actually do start reproducing the works of Shakespeare -- word perfect, from their first keystroke.)
Lee Smolin is "convinced that quantum mechanics is not a final theory. I believe this because I have never encountered an interpretation of the present formulation of quantum mechanics that makes sense to me."
And Leon Lederman (former director of Fermilab, author of The God Particle and a nice guy, who answered a fan e-mail I sent him a long time ago) says: " To believe without knowing it cannot be proved (yet) is the essence of physics. Guys like Einstein, Dirac, Poincaré, etc. extolled the beauty of concepts, in a bizarre sense, placing truth at a lower level of importance."
There are a hundred and twenty contributors, all told, but the responses are short. Browse through them, and see who has the most guts.