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 universes branching off ours 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. See also my follow-up post, Is Science Infinite? –John Horgan

Horgan: Are you as optimistic now as when you wrote The Beginning of Infinity?

Deutsch: What I call optimism is the proposition that all evils are due to a lack of knowledge, and that knowledge is attainable by the methods of reason and science. I think the arguments against that proposition are as untenable as ever. 

I'm also “optimistic” in the sense that I expect progress to continue in the future. I'm even a little more so now than I was, because I see that the idea of it is catching on.

Horgan: Do you really, truly, believe in existence of other universes, as implied by the many-worlds hypothesis?

Deutsch: It's my opinion that the state of the arguments, and evidence, about other universes closely parallels that about dinosaurs. Namely: they're real – get over it.

But I think that belief is an irrational state of mind and I try to avoid it. As Popper said: “I am opposed to the thesis that the scientist must believe in his theory. As far as I am concerned ‘I do not believe in belief,’ as E. M. Forster says; and I especially do not believe in belief in science.” (Actually Forster's view was much more equivocal than Popper's on this.) 

Horgan: Do you ever wonder whether our universe is a simulation created by super-intelligent aliens?

Deutsch: I reject all explanations involving the supernatural, including that one.

Horgan: Will science ever explain why there’s something rather than nothing?

Deutsch: Science can't, but philosophy in the light of scientific theories could. I expect that once it does, we'll also realize that that way of asking the question is misleading. Like “who designed the animals” was.

Horgan: Do you believe in what Steven Weinberg has called a “final theory” in physics?

Deutsch: No. I guess that deeper theories will always reveal still deeper problems. (“Deeper” doesn't necessarily mean “in terms of ever smaller constituents,” by the way.)

Horgan: Edward Witten has said that consciousness “will always remain a mystery.” What do you think?

Deutsch: I think nothing worth understanding will always remain a mystery. And consciousness (qualia, creativity, free will etc.) seems eminently worth understanding.

Horgan: If science finds a solution to consciousness, will it have something to do with quantum mechanics?

Deutsch: No.

Horgan: Why not?

Deutsch: I know of no arguments that it should be expected to, other than ones based on misconceptions about quantum theory.

Horgan: Do you believe in free will?

Deutsch: People mean different things by the term. The multiverse is deterministic so “ability to violate the laws of physics” doesn't exist. Nor does “having an effect in the gaps between laws of physics.” There are no such gaps. But the ability to create something new that is not *explained* by the laws of physics (laws of motion plus initial conditions of the universe), does. We do it all the time. Explanation is not the same as prediction – even prediction in principle.

Horgan: What worries you most about the world today?

Deutsch: Weapons of mass destruction in the hands of people with evil ideologies. And the lack of any plan – indeed the systematic stigmatization of all plans – to defend people from them.

Horgan: Do you think concerns about climate change and other environmental problems are excessive?

Deutsch: Resource-depletion and overpopulation worries are fundamentally flawed. Climate change worries are fundamentally misdirected. Geoengineering is essential, unavoidable and is being downplayed and delayed because of the “moral hazard” that people will be distracted from reducing carbon dioxide emissions. The latter should be the third most important response, after geoengineering and mitigation of the effects of climate (changed and otherwise) on people.

Horgan: Do you think world peace--the end of war and even the threat of war between nations--is possible?

Deutsch: Yes. The existence of war and the threat of war is an evil. All evils are due to lack of knowledge (see the chapter on Optimism in The Beginning of Infinity), and there are no insuperable impediments to the creation of knowledge other than laws of physics.

Horgan: Are you working on a new book? If so, can you describe it a little?

Deutsch: Working title: “Irrationality.” Working subtitle: “An exploration of what works and what doesn’t.” No promises to stick to that.

Horgan: What’s your utopia?

Deutsch: Of course I'm opposed to utopianism. Progress comes only through piecemeal, tentative improvements. I think the world will never be perfected, even when everything we think of as problematic today has been eliminated. We shall always be at the beginning of infinity. Never satisfied.

Further Reading:

Is Science Infinite?

See Q&As with Steven WeinbergGeorge EllisCarlo RovelliEdward WittenScott AaronsonSabine HossenfelderPriyamvada NatarajanGarrett LisiPaul SteinhardtLee SmolinRobin HansonEliezer YudkowskyStuart KauffmanChristof KochRupert Sheldrake, Sheldon Solomon, and Stephen Wolfram.

How Physics Lost Its Fizz

Was I Wrong about ‘The End of Science’?

Is David Deutsch's Vision of Endless Understanding Delusional?

See also my 2011 interview with Deutsch.