Finding Our Way
A Conversation with David Deutsch
David Deutsch has a talent for expressing scientifically and philosophically revolutionary ideas in deceptively simple language. He is a visiting professor of physics at the Center for Quantum Computation at the Clarendon Laboratory of Oxford University, where he works on the quantum theory of computation, and constructor theory.
This chapter features two of our conversations. In the first, we focus on the surprising power and reach of human knowledge, the future of artificial intelligence, and the survival of civilization.
After our first conversation, Deutsch read my book The Moral Landscape and wanted to discuss it. He intended to do this privatelyâprobably because he disagreed with much of it and didnât want to break the news to me on my own podcast. But I urged him to let me record our conversation, because if he was going to dismantle my cherished thesis, I wanted it done in public. Given all that was covered in our first meeting, we hit the ground running.
In this second conversation, we further explore the nature of knowledge and the implications of its being independent of any specific, physical embodiment. This is one of the things that make Davidâs views on more ordinary topics so interesting. As a physicist, his understanding of something as mundane as why itâs wrong to coerce people to do things they donât want to do connects directly to his view of how knowledge ultimately accumulates in the cosmos. His ideas are fairly startlingâand unlike most scientific thinking about our place in nature, they put us somewhere near the center of the drama.
Harris: David, I want to creep up on your central thesis. Certain claims you makeâspecifically, about the reach and power of human knowledgeâare fairly breathtaking. And I want to agree with them in the end, because theyâre so hopeful. But I have a few quibbles.
Deutsch: Sure. But I should say first that while I think the outlook is positive, the future is unpredictable. Nothing is guaranteed. Thereâs no guarantee that civilization or our species will survive, but there is a guarantee that we know in principle how both can survive.
Harris: Before we get into your theory, letâs start somewhere near epistemological bedrock. Iâd like to get to a definition of terms, because in The Beginning of Infinity you use words like âknowledgeâ and âexplanationâ and even âpersonâ in novel ways, and I want to make clear just how much work youâre requiring those words to do. Letâs begin with the concept of knowledge. What is it, in your view?
Deutsch: The way I think of knowledge is broader than the usual use of the termâand yet, paradoxically, closer to its commonsense use. Knowledge is a kind of information, which is to say that itâs something that is one particular way and could have been otherwise; additionally, knowledge says something true and useful about the world.
Knowledge is in a sense an abstraction, because itâs independent of its physical instantiation. I can speak words which embody some knowledge. I can write them down. They can exist as movements of electrons in a computer, and so on. So knowledge isnât dependent on any particular instantiation. But it does have the property that when it is instantiated, it tends to remain so. Letâs say a scientist writes down a speculation that turns out to be a genuine piece of knowledge. Thatâs the only version he doesnât throw in the wastebasket. Thatâs the version that will be published, that will be studied by other scientists, and so on.
So knowledge is a piece of information that has the property of tending to stay physically instantiated. Once you think of knowledge that way, you realize that, for example, the pattern of base pairs in a geneâs DNA also constitutes knowledge, in line with Karl Popperâs concept of knowledge as not requiring a knowing subject. It can exist in books, or in the mind, and people can have knowledge they donât know they have.
Harris: A few more definitions: in your view, whatâs the boundary between science and philosophy, or between science and other expressions of rationality? In my experience, people are profoundly confused about this, including many scientists. Iâve argued for years about the unity of knowledge, and I feel youâre a kindred spirit here. How do you differentiateâor do you differentiateâscience and philosophy?
Deutsch: Well, theyâre both manifestations of reason. But among the rational approaches to knowledge, thereâs an important difference between science and things like philosophy and mathematics. Not at the most fundamental level, but at a level which is often of great practical importance. That is, science is the kind of knowledge that can be tested by experiment or observation. I hasten to add, that doesnât mean that the content of a scientific theory consists entirely of its testable predictions; the testable predictions of a typical scientific theory are a tiny sliver of what it tells us about the world. Karl Popper introduced this criterion, that science is testable theories and everything else is untestable. Ever since, people have falsely interpreted him as saying that only scientific theories can have meaning. That would be a kind of positivism, but he was really the opposite of a positivist. His own theories arenât scientific, theyâre philosophical, and yet he doesnât consider them meaningless. In the bigger picture, the more important distinction that should be uppermost in our minds is the one between reason and unreason.
Harris: The widespread notion is that science reduces to what is testable, and that any claim you canât measure is somehow vacuous. So, too, is the belief that there exists a bright line between science and every other discipline where we purport to describe reality. Itâs as if the architecture of a university had defined peopleâs thinking: you go to the chemistry department to talk about chemistry, you go to the journalism department to talk about current events, you go to the history department to talk about human events in the past. This has balkanized the thinking of even very smart people and convinced them that all these language games are irreconcilable and that thereâs no common project.
Take something like the assassination of Mahatma Gandhi. That was a historical event. However, anyone who purports to doubt that it occurredâanyone who says, âActually, Gandhi was not assassinated. He went on to live a long and happy life in the Punjab under an assumed nameââwould be making a claim that is at odds with the data. Itâs at odds with the testimony of people who saw Gandhi assassinated and with the photographs we have of him lying in state. The task is to reconcile the claim that he was not assassinated with the facts we know to be true.
That task doesnât depend on what someone in a white lab coat has said, or facts that have been discovered in a laboratory funded by the National Science Foundation. Itâs the distinction between having good reasons for what you believe and having bad onesâand thatâs a distinction between reason and unreason, as you put it. While one sounds more like a journalist or a historian when talking about the assassination of Gandhi, it would be deeply unscientific to doubt that it occurred.
Deutsch: I wouldnât put it in terms of reasons for belief. But I agree with you that people have wrong ideas about what science is and what the boundaries of scientific thinking are, and what sort of thinking should be taken seriously and what shouldnât. I think itâs slightly unfair to put the blame on universities here. This misconception arose originally for good reasons. Itâs rooted in the empiricism of the eighteenth century, when science had to rebel against the authority of tradition and to defend new forms of knowledge that involved observation and experimental tests.
Empiricism is the idea that knowledge comes to us through the senses. Now, thatâs completely false: all knowledge is conjectural. It first comes from within and is intended to solve problems, not to summarize data. But this idea that experience has authority, and that only experience has authorityâfalse though it isâwas a wonderful defense against previous forms of authority, which were not only invalid but stultifying. But in the twentieth century, a horrible thing happened, which is that people started taking empiricism seriouslyânot just as a defense, but as being literally trueâand that almost killed certain sciences. Even within physics; it greatly impeded progress in quantum theory.
So to make a little quibble of my own, I think the essence of what we want in science are not justified beliefs but good explanations. You can conduct science without ever believing in a theory, just as a good policeman or judge can implement the law without believing either the case for the prosecution or the case for the defenseâbecause they know that a particular system of law is better than any individual humanâs opinion.
The same is true of science. Science is a way of dealing with theories regardless of whether or not one believes them. One judges them according to whether or not theyâre good explanations. And if a particular explanation ends up being the only explanation that survives the intense criticism that reason and science can apply, whether or not that includes experimental testing, then itâs not so much adopted at that point as just not discarded. It has survived for the moment.
Harris: I understand that youâre pushing back against the notion that we need to find some ultimate foundation for our knowledge, encouraging instead this open-ended search for better explanations. But letâs table that for a moment. Letâs address the notion of scientific authority. Itâs often said that, in science, we donât rely on authority. But thatâs both true and not true. We do rely on it in practice, if only in the interest of efficiency. If I ask you a question about physics, Iâll tend to believe your answer, because youâre a physicist and Iâm not. And if what you say contradicts something Iâve heard from another physicist, then, if it matters to me, Iâll look into it more deeply and try to figure out the nature of the dispute.
But if there are any points on which all physicists agree, a nonphysicist like me will defer to the authority of that consensus. Again, this is less a statement of epistemology than it is a statement about the specialization of knowledge and the unequal distribution of human talentâand, frankly, the shortness of every human life. We simply donât have time to check everyoneâs work, and sometimes we have to rely on faith that the system of scientific conversation is correcting for errors, self-deception, and fraud.
Deutsch: Yes, exactly. You could call that consensus âauthority.â But every student who wants to make a contribution to a science is hoping to find something about which every scientist in the field is wrong. So itâs not irrational to claim one is right and every expert in the field is wrong. When we consult experts, itâs not quite because we think theyâre more competent. You referred to error correction, and that hits the nail on the head. If I consult a doctor about what my treatment should be, I assume that the process leading to his recommendation is the same one I would have adopted if Iâd had the time and the background and the interest to go to medical school. Now, it might not be exactly the same, and I might also take the view that there are ...