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Physicist, University of Oxford; Author, The Beginning of Infinity; Recipient, Edge Computation Science Prize
And why?

"What Questions Have Disappeared...And Why?" Funny you should ask that. "And why? " could itself be the most important question that has disappeared from many fields.

"And why?": in other words, "what is the explanation for what we see happening?" "What is it in reality that brings about the outcome that we predict?" Whenever we fail to take that question seriously enough, we are blinded to gaps in our favoured explanation. And so, when we use that explanation to interpret regularities that we may observe, instead of understanding that the explanation was an assumption in our analysis, we regard it as the inescapable implication of our observations.

"I just can't feel myself split", complained Bryce DeWitt when he first encountered the many-universes interpretation of quantum theory. Then Hugh Everett convinced him that this was the same circular reasoning that Galileo rejected when he explained how the Earth can be in motion even though we observe it to be at rest. The point is, both theories are consistent with that observation. Thanks to Everett, DeWitt and others, the "and why" question began gradually to return to quantum theory, whence it had largely disappeared during the 1930s. I believe that its absence did great harm both in impeding progress and in encouraging all sorts of mystical fads and pseudo-science. But elsewhere, especially in the human philosophies (generally known as social sciences), it is still largely missing. Although behaviourism — the principled refusal to ask "and why?" — is no longer dominant as an explicit ideology, it is still widespread as a psychological attitude in the human philosophies.

Suppose you identified a gene G, and a human behaviour B, and you undertook a study with 1000 randomly chosen people, and the result was that of the 500 people who had G in their genome, 499 did B, while of the 500 who lacked G, 499 failed to do B. You'd conclude, wouldn't you, that G is the predominant cause of B? Obviously there must be other mechanisms involved, but they have little influence on whether a person does B or not. You'd inform the press that all those once-trendy theories that tried to explain B through people's upbringing or culture, or attributed it to the exercise of free will or the logic of the situation or any combination of such factors — were just wrong. You've proved that when people choose to do B, they are at the very least responding to a powerful influence from their genes. And if someone points out that your results are perfectly consistent with B being 100% caused by something other than G (or any other gene), or with G exerting an influence in the direction of not doing B, you will shrug momentarily, and then forget that possibility. Won't you?

DAVID DEUTSCH's research in quantum physics has been influential and highly acclaimed. His papers on quantum computation laid the foundations for that field, breaking new ground in the theory of computation as well as physics, and have triggered an explosion of research efforts worldwide. He is a member of the Centre for Quantum Computation at the Clarendon Laboratory, Oxford University and the author of The Fabric of Reality.