The Infinite Optimism of Physicist David Deutsch

Some thinkers, even if I disagree with them, jolt me in a way I like. They knock me so askew that the world gets weird again, in a good way. Physicist David Deutsch is such a thinker. He is renowned for his ideas about quantum computation, and for his insistence that the many-worlds interpretation of quantum mechanics is true. Those hypothetical other universes branching off of ours at every instant really exist! In 2011 I immersed myself in Deutsch’s worldview when The Wall Street Journal asked me to review his book The Beginning of Infinity: Explanations that Transform the World, which argues that the quest for knowledge is infinite. Although he critiques my book The End of Science, I found Deutsch’s radical optimism so fascinating that I gave Infinity a rave review. “Deutsch makes the case for infinite progress with such passion, imagination and quirky brilliance,” I wrote, “that I couldn't help but enjoy his company. In fact, more often than not I found myself agreeing with him—or at the very least hoping that he's right.” My optimism has been flagging lately, so I reached out to Deutsch for a booster shot, and we had the following email exchange. –John Horgan