David Deutsch Quotes

The whole [scientific] process resembles biological evolution. A problem is like an ecological niche, and a theory is like a gene or a species which is being tested for viability in that niche.

an unproblematic state is a state without creative thought. Its other name is death.

All fiction that does not violate the laws of physics is fact.

Some people become depressed at the scale of the universe, because it makes them feel insignificant. Other people are relieved to feel insignificant, which is even worse. But, in any case, those are mistakes. Feeling insignificant because the universe is large has exactly the same logic as feeling inadequate for not being a cow. Or a herd of cows. The universe is not there to overwhelm us; it is our home, and our resource. The bigger the better.

Without error-correction all information processing, and hence all knowledge-creation, is necessarily bounded. Error-correction is the beginning of infinity.

Good political institutions are those that make it as easy as possible to detect whether a ruler or policy is a mistake, and to remove rulers or policies without violence when they are.

Like every other destruction of optimism, whether in a whole civilisation or in a single individual, these must have been unspeakable catastrophes for those who had dared to expect progress. But we should feel more than sympathy for those people. We should take it personally. For if any of those earlier experiments in optimism had succeeded, our species would be exploring the stars by now, and you and I would be immortal.

Base metals can be transmuted into gold by stars, and by intelligent beings who understand the processes that power stars, but by nothing else in the universe.

We do not experience time flowing, or passing. What we experience are differences between our present perceptions and our present memories of past perceptions. We interpret those differences, correctly, as evidence that the universe changes with time. We also interpret them, incorrectly, as evidence that our consciousness, or the present, or something, moves through time.

It is a mistake to conceive of choice and decision-making as a process of selecting from existing options according to a fixed formula. That omits the most important element of decision-making, namely the creation of new options.

objective knowledge is indeed possible: it comes from within! It begins as conjecture, and is then corrected by repeated cycles of criticism, including comparison with the evidence on our ‘wall’.

Feeling insignificant because the universe is large has exactly the same logic as feeling inadequate for not being a cow.

the universe is not only queerer than we suppose, but queerer than we can suppose.

As David Deutsch says, “Everything that is not forbidden by laws of nature is achievable, given the right knowledge".

There is only one way of thinking that is capable of making progress, or of surviving in the long run, and that is the way of seeking good explanations through creativity and criticism. What

The theory of computation has traditionally been studied almost entirely in the abstract, as a topic in pure mathematics. This is to miss the point of it. Computers are physical objects, and computations are physical processes. What computers can or cannot compute is determined by the laws of physics alone, and not by pure mathematics.

Optimism is, in the first instance, a way of explaining failure, not prophesying success. It says that there is no fundamental barrier, no law of nature or supernatural decree, preventing progress. Whenever

It follows that humans, people and knowledge are not only objectively significant: they are by far the most significant phenomena in nature – the only ones whose behaviour cannot be understood without understanding everything of fundamental importance.

history is the history of ideas, not of the mechanical effects of biogeography. Strategies to prevent foreseeable disasters are bound to fail eventually, and cannot even address the unforeseeable. To prepare for those, we need rapid progress in science and technology and as much wealth as possible.

Because we are universal explainers, we are not simply obeying our genes. For

Science is what we have learned about how to keep from fooling ourselves.’ By

If something is permitted by the laws of physics, then the only thing that can prevent it from being technologically possible is not knowing how.

My pencil and I are more clever than I.

SOCRATES: No, I am not sure of anything. I never have been. But the god explained to me why that must be so, starting with the fallibility of the human mind and the unreliability of sensory experience.

The ability to create and use explanatory knowledge gives people a power to transform nature which is ultimately not limited by parochial factors, as all other adaptations are, but only by universal laws. This is the cosmic significance of explanatory knowledge – and hence of people, whom I shall henceforward define as entities that can create explanatory knowledge.

Trying to rely on the sheer good luck of avoiding bad outcomes indefinitely would simply guarantee that we would eventually fail without the means of recovering.

We never know any data before interpreting it through theories. All observations are, as Popper put it, theory-laden,* and hence fallible, as all our theories are. Consider

We shall always be faced with the problem of how to plan for an unknowable future.

a rational political system makes it as easy as possible to detect, and persuade others, that a leader or policy is bad, and to remove them without violence if they are.

An optimistic civilization is open and not afraid to innovate, and is based on traditions of criticism.

Like an explosive awaiting a spark, unimaginably numerous environments in the universe are waiting out there, for aeons on end, doing nothing at all or blindly generating evidence and storing it up or pouring it out into space. Almost any of them would, if the right knowledge ever reached it, instantly and irrevocably burst into a radically different type of physical activity: intense knowledge-creation, displaying all the various kinds of complexity, universality and reach that are inherent in the laws of nature, and transforming that environment from what is typical today into what could become typical in the future. If we want to, we could be that spark.

systems of government are to be judged not for their prophetic ability to choose and install good leaders and policies, but for their ability to remove bad ones that are already there.

All beliefs about matters of fact or real existence are derived merely from something that is present to the memory or senses, and a customary association of that with some other thing.

The most important of all limitations on knowledge – creation is that we cannot prophecy: we cannot predict the content of ideas yet to be created, or their effects. This limitation is not only consistent with the unlimited growth of knowledge, it is entailed by it.

To interpret dots in the sky as white-hot, million-kilometre spheres, one must first have thought of the idea of such spheres. And then one must explain why they look small and cold and seem to move in lockstep around us and do not fall down. Such ideas do not create themselves, nor can they be mechanically derived from anything: they have to be guessed – after which they can be criticized and tested.

Amending the ‘data’, or rejecting some as erroneous, is a frequent concomitant of scientific discovery, and the crucial ‘data’ cannot even be obtained until theory tells us what to look for and how and why.

Sparta has no philosophers. That’s because the job of a philosopher is to understand things better, which is a form of change, so they don’t want it. Another difference: they don’t honour living poets, only dead ones. Why? Because dead poets don’t write anything new, but live ones do. A third difference: their education system is insanely harsh; ours is famously lax. Why? Because they don’t want their kids to dare to question anything, so that they won’t ever think of changing anything. How

As the physicist Stephen Hawking put it, humans are ‘just a chemical scum on the surface of a typical planet that’s in orbit round a typical star on the outskirts of a typical galaxy’. The proviso ‘in the cosmic scheme of things’ is necessary because the chemical scum evidently does have a special significance according to values that it applies to itself, such as moral values. But the Principle says that all such values are themselves anthropocentric: they explain only the behaviour of the scum, which is itself insignificant.

But in any case, understanding is one of the higher functions of the human mind and brain, and a unique one. Many other physical systems, such as animals’ brains, computers and other machines, can assimilate facts and act upon them. But at present we know of nothing that is capable of understanding an explanation – or of wanting one in the first place – other than a human mind.

Although, through the vagaries of international politics, Athens became independent and democratic again soon afterwards, and continued for several generations to produce art, literature and philosophy, it was never again host to rapid, open-ended progress. It became unexceptional. Why? I guess that its optimism was gone.

Those two overarching concerns are these: we Athenians are concerned above all with improvement; the Spartans seek only – stasis. Two opposite objectives. If

Copenhagen interpretation Niels Bohr’s combination of instrumentalism, anthropocentrism and studied ambiguity, used to avoid understanding quantum theory as being about reality.

Existimos en múltiples versiones en universos denominados «momentos».

They are also about coherence, elegance and simplicity, as opposed to arbitrariness and complexity, though none of those things is easy to define either.

The Principle of Optimism All evils are caused by insufficient knowledge.

Its quest for good explanations corrects the errors, allows for the biases and misleading perspectives, and fills in the gaps.

This is what we can achieve when, as Feynman said, we keep learning more about how not to fool ourselves.

The Enlightenment (The beginning of) a way of pursuing knowledge with a tradition of criticism and seeking good explanations instead of reliance on authority.

Very little in nature is detectable by unaided human senses.

This inductively justifies the conclusion that induction cannot justify any conclusions.

everything that is not forbidden by laws of nature is achievable, given the right knowledge.

David Deutsch, in The Fabric of Reality, embraces the ‘many worlds’ interpretation of quantum theory,

Perhaps a more practical way of stressing the same truth would be to frame the growth of knowledge (all knowledge, not only scientific) as a continual transition from problems to better problems, rather than from problems to solutions or from theories to better theories. This

a population of replicators subject to variation (for instance by imperfect copying) will be taken over by those variants that are better than their rivals at causing themselves to be replicated.

The most general way of stating the central assertion of the neo-Darwinian theory of evolution is that a population of replicators subject to variation (for instance by imperfect copying) will be taken over by those variants that are better than their rivals at causing themselves to be replicated. This

Because pessimism needs to counter that argument in order to be at all persuasive, a recurring theme in pessimistic theories throughout history has been that an exceptionally dangerous moment is imminent.

Whenever we observe anything – a scientific instrument or a galaxy or a human being – what we are actually seeing is a single-universe perspective on a larger object that extends some way into other universes. In

Scientists and inventors alike, they first guess a new explanation—a hypothesis—as wild and innovative as they can conjure. And then they test it rigorously, their hearts filled with the hope they’ll find a door or a window that reframes their understanding of the universe, of life, of a flower, or a cure for cancer. And it all starts with a guess, a good explanation as unlikely as it is plausible. A story at the knife’s edge of innovation, bleeding truth and pushing the limits of knowledge further afield. That impossibly sharp place where dreams and reality converge. A hard-to-vary idea as powerful as the one that broke Einstein’s General Relativity and his assumption that the laws of nature don’t depend on the motion of an observer.

If two programs respond in the same way to every possible action by the user, then they render the same environment; if they would respond perceptibly differently to even one possible action, they render different environments.

Whenever a wide range of variant theories can account equally well for the phenomenon they are trying to explain, there is no reason to prefer one of them over the others, so advocating a particular one in preference to the others is irrational.

Das Fegen der Wandelgänge ist eine lästige Angelegenheit an diesem Nachmittag: Kaum sind die Blätter und Piniennadeln zusammengekehrt, bläst der Wind den Haufen davon. Wolken ziehen über dem Kahlen Gipfel auf und verschütten eisigen Nieselregen.

mechanical reinterpretations of human affairs not only lack explanatory power, they are morally wrong as well, for in effect they deny the humanity of the participants, casting them and their ideas merely as side effects of the landscape. Diamond

Using our explanations, we ‘see’ right through the behaviour to the meaning. Parrots copy distinctive sounds; apes copy purposeful movements of a certain limited class. But humans do not especially copy any behaviour. They use conjecture, criticism and experiment to create good explanations of the meaning of things – other people’s behaviour, their own, and that of the world in general. That

Arthur C. Clarke once remarked that 'any sufficiently advanced technology is indistinguishable from magic'. This is true, but slightly misleading. It is stated from the point of view of a pre-scientific thinker, which is the wrong way round. The fact is that to anyone who understands what virtual reality is, even genuine magic would be indistinguishable from technology, for there is no room for magic in a comprehensible reality. Anything that seems incomprehensible is regarded by science merely as evidence that there is something we have not yet understood, be it a conjuring trick, advanced technology or a new law of physics.

Whenever we try to improve things and fail, it is not because the spiteful (or unfathomably benevolent) gods are thwarting us or punishing us for trying, or because we have reached a limit on the capacity of reason to make improvements, or because it is best that we fail, but always because we did not know enough, in time.

The scientific revolution was part of a wider intellectual revolution, the Enlightenment, which also brought progress in other fields, especially moral and political philosophy, and in the institutions of society. Unfortunately, the term ‘the Enlightenment’ is used by historians and philosophers to denote a variety of different trends, some of them violently opposed to each other. What I mean by it will emerge here as we go along. It is one of several aspects of ‘the beginning of infinity’, and is a theme of this book. But one thing that all conceptions of the Enlightenment agree on is that it was a rebellion, and specifically a rebellion against authority in regard to knowledge.

I have settled on a simple test for judging claims, including Dennett’s, to have explained the nature of consciousness (or any other computational task): if you can’t program it, you haven’t understood it. Turing invented his test in the hope of bypassing all those philosophical problems. In other words, he hoped that the functionality could be achieved before it was explained. Unfortunately it is very rare for practical solutions to fundamental problems to be discovered without any explanation of why they work.

SOCRATES: You have? Oh – you said that you honour Athenians for our openness to persuasion. And for our defiance of bullies. But

El tiempo no transcurre. Otros tiempos son, simplemente, casos especiales de otros universos.

The last room number is not infinity. First of all, there is no last room.

One of the consequences of optimism is that one expects to learn from failure – one’s own and others’.

knowledge has the unique ability to take aim at a distant target and utterly transform it while having scarcely any effect on the space between.

Not only is there constant backtracking, but the many subproblems all remain simultaneously active and are addressed opportunistically.

There is an explanatory link between ought and is, and this provides one of the ways in which reason can indeed address moral issues.

The theory reaches out, as it were, from its finite origins inside one brain that has been affected only by scraps of patchy evidence from a small part of one hemisphere of one planet – to infinity. This reach of explanations is another meaning of ‘the beginning of infinity’. It is the ability of some of them to solve problems beyond those that they were created to solve.

inventing falsehoods is easy, and therefore they are easy to vary once found; discovering good explanations is hard, but the harder they are to find, the harder they are to vary once found.

So we seek explanations that remain robust when we test them against those flickers and shadows, and against each other, and against criteria of logic and reasonableness and everything else we can think of. And when we can change them no more, we have understood some objective truth. And, as if that were not enough, what we understand we then control. It is like magic, only real. We are like gods!

It would be astonishing if the details of a primitive, static society’s collapse had any relevance to hidden dangers that may be facing our open, dynamic and scientific society, let alone what we should do about them.

It is a mistake to conceive of choice and decision-making as a process of selecting from existing options according to a fixed formula. That omits the most important element of decision-making, namely the creation of new options. Good

We know that achieving arbitrary physical transformations that are not forbidden by the laws of physics (such as replanting a forest) can only be a matter of knowing how. We know that finding out how is a matter of seeking good explanations.

No somos únicamente «escoria química» pues que, por ejemplo, el comportamiento general de nuestro planeta, nuestra estrella y nuestra galaxia depende de una magnitud física emergente, pero fundamental: el conocimiento que hay en dicha escoria.

For each natural number N, will the guest in room number N please move immediately to room number N (N +1)/2.’ Then they announce, ‘For all natural numbers N and M, will the Nth passenger from the Mth train please go to room number [(N + M)2 + N – M/2.

To choose an option, rationally, is to choose the associated explanation. Therefore, rational decision-making consists not of weighing evidence but of explaining it, in the course of explaining the world. One judges arguments as explanations, not justifications, and one does this creatively, using conjecture, tempered by every kind of criticism. It is in the nature of good explanations – being hard to vary – that there is only one of them. Having created it, one is no longer tempted by the alternatives. They have been not outweighed, but out-argued, refuted and abandoned. During the course of a creative process, one is not struggling to distinguish between countless different explanations of nearly equal merit; typically, one is struggling to create even one good explanation, and, having succeeded, one is glad to be rid of the rest.

Lo que consideramos nuestras acciones «libres» no son las aleatorias o indeterminadas, sino las que están ampliamente «determinadas» por quienes somos, cómo pensamos y qué está en juego. (Si bien están ampliamente determinadas, pueden ser muy impredecibles por razones de complejidad.)

In some environments in the universe, the most efficient way for humans to thrive might be to alter their own genes. Indeed, we are already doing that in our present environment, to eliminate diseases that have in the past blighted many lives. Some people object to this on the grounds (in effect) that a genetically altered human is no longer human. This is an anthropomorphic mistake. The only uniquely significant thing about humans (whether in the cosmic scheme of things or according to any rational human criterion) is our ability to create new explanations, and we have that in common with all people. You do not become less of a person if you lose a limb in an accident; it is only if you lose your brain that you do. Changing our genes in order to improve our lives and to facilitate further improvements is no different in this regard from augmenting our skin with clothes or our eyes with telescopes.

The biologist Peter Medawar described science as ‘the art of the soluble’, but the same applies to all forms of knowledge. All kinds of creative thought involve judgements about what approaches might or might not work. Gaining or losing interest in particular problems or sub-problems is part of the creative process and itself constitutes problem-solving. So whether ‘problems are soluble’ does not depend on whether any given question can be answered, or answered by a particular thinker on a particular day. But if progress ever depended on violating a law of physics, then ‘problems are soluble’ would be false.

Consider also the revolutionary utopians, who typically achieve only destruction and stagnation. Though they are blind optimists, what defines them as utopians is their pessimism that their supposed utopia, or their violent proposals for achieving and entrenching it, could ever be improved upon. Additionally,

The whole motivation for seeking a perfectly secure foundation for mathematics was mistaken. It was a form of justificationism. Mathematics is characterized by its use of proofs in the same way that science is characterized by its use of experimental testing; in neither case is that the object of the exercise. The object of mathematics is to understand – to explain – abstract entities. Proof is primarily a means of ruling out false explanations; and sometimes it also provides mathematical truths that need to be explained. But, like all fields in which progress is possible, mathematics seeks not random truths but good explanations.

The fundamental theories of modern physics explain the world in jarringly counter-intuitive ways. For example, most non-physicists consider it self-evident that when you hold your arm out horizontally you can feel the force of gravity pulling it downwards. But you cannot. The existence of a force of gravity is, astonishingly, denied by Einstein’s general theory of relativity, one of the two deepest theories of physics. This says that the only force on your arm in that situation is that which you yourself are exerting, upwards, to keep it constantly accelerating away from the straightest possible path in a curved region of spacetime

Conjectures are the products of creative imagination. But the problem with imagination is that it can create fiction much more easily than truth. As I have suggested, historically, virtually all human attempts to explain experience in terms of a wider reality have indeed been fiction, in the form of myths, dogma and mistaken common sense – and the rule of testability is an insufficient check on such mistakes. But the quest for good explanations does the job: inventing falsehoods is easy, and therefore they are easy to vary once found; discovering good explanations is hard, but the harder they are to find, the harder they are to vary once found.

Some people become depressed at the scale of the universe, because it makes them feel insignificant. Other people are relieved to feel insignificant, which is even worse. But, in any case, those are mistakes. Feeling insignificant because the universe is large has exactly the same logic as feeling inadequate for not being a cow.

The very existence of Athens, however peaceful, is a deadly threat to Sparta’s stasis. And therefore, in the long run, the condition for the continued stasis of Sparta (which means its continued existence, as they see it) is the destruction of progress in Athens (which from our perspective would constitute the destruction of Athens).

From the least parochial perspectives available to us, people are the most significant entities in the cosmic scheme of things. They are not ‘supported’ by their environments, but support themselves by creating knowledge. Once they have suitable knowledge (essentially, the knowledge of the Enlightenment), they are capable of sparking unlimited further progress.

The misconception that knowledge needs authority to be genuine or reliable dates back to antiquity, and it still prevails. To this day, most courses in the philosophy of knowledge teach that knowledge is some form of justified, true belief, where ‘justified’ means designated as true (or at least ‘probable’) by reference to some authoritative source or touchstone of knowledge. Thus ‘how do we know…?’ is transformed into ‘by what authority do we claim…?

Rejecting authority in regard to knowledge was not just a matter of abstract analysis. It was a necessary condition for progress, because, before the Enlightenment, it was generally believed that everything important that was knowable had already been discovered, and was enshrined in authoritative sources such as ancient writings and traditional assumptions. Some of those sources did contain some genuine knowledge, but it was entrenched in the form of dogmas along with many falsehoods. So the situation was that all the sources from which it was generally believed knowledge came actually knew very little, and were mistaken about most of the things that they claimed to know. And therefore progress depended on learning how to reject their authority. This is why the Royal Society (one of the earliest scientific academies, founded in London in 1660) took as its motto ‘Nullius in verba’, which means something like ‘Take no one’s word for it.

I think that there is only one way to science – or to philosophy, for that matter: to meet a problem, to see its beauty and fall in love with it; to get married to it and to live with it happily, till death do ye part – unless you should meet another and even more fascinating problem or unless, indeed, you should obtain a solution. But even if you do obtain a solution, you may then discover, to your delight, the existence of a whole family of enchanting, though perhaps difficult, problem children…

There is often a moral overtone to reductionism (science should be essentially reductive). This is related both to instrumentalism and to the Principle of Mediocrity, which I criticized in Chapters 1 and 3. Instrumentalism is rather like reductionism except that, instead of rejecting only high-level explanations, it tries to reject all explanations. The Principle of Mediocrity is a milder form of reductionism: it rejects only high-level explanations that involve people. While I am on the subject of bad philosophical doctrines with moral overtones, let me add holism, a sort of mirror image of reductionism. It is the idea that the only valid explanations (or at least the only significant ones) are of parts in terms of wholes. Holists also often share with reductionists the mistaken belief that science can only (or should only) be reductive, and therefore they oppose much of science. All those doctrines are irrational for the same reason: they advocate accepting or rejecting theories on grounds other than whether they are good explanations.

The meaning of life is something we are using creativity to discover, to build. We can’t find the meaning of life in the world ‘out there’, nor just by pure thought, or by reference to an authority. What we have to do is form explanations about what is right and wrong, what is better and worse, what is beautiful and ugly, and hone those theories, while also trying to meet them. At any one moment, we will meet them imperfectly, just like scientific theories, at any one moment, are only an imperfect explanation of what the physical world is like. But, through criticism and conjecture and seeking the truth, we can resolve the errors in what we had previously thought and thereby make progress.

To truly understand the Nazis,” Ulmstrom said, leading the way, “you have to stop considering them as a political party. They called themselves Nationalsozialistische Deutsche Arbeiterpartei—the National Socialist German Workers’ Party—but in reality, they were really a cult.” “A cult?” Gray asked. “They bore all the trappings, ja? A spiritual leader who could not be questioned, disciples who wore matching clothes, rituals and blood oaths performed in secret, and most important of all, the creation of a potent totem to worship. The Hakenkreuz. The Broken Cross, also called the swastika. A symbol to supplant the crucifix and the Star of David.” “Hari krishnas on steroids,” Monk mumbled. “Do not joke. The Nazis understood the inherent power of ideas. A power greater than any gun or rocket. They used it to subjugate and brainwash an entire nation.

The argument of Chapter 2, applied to any interference phenomenon destroys the classical idea that there is only one universe. Logically, the possibility of complex quantum computations adds nothing to a case that is already unanswerable. But it does add psychological impact. With Shor’s algorithm, the argument has been writ very large. To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s algorithm works. I do not merely mean predict that it will work, which is merely a matter of solving a few uncontroversial equations. I mean provide an explanation. When Shor’s algorithm has factorized a number, using 10500 or so times the computational resources that can be seen to be present, where was the number factorized? There are only about 1080 atoms in the entire visible universe, an utterly minuscule number compared with 10500. So if the visible universe were the extent of physical reality, physical reality would not even remotely contain the resources required to factorize such a large number. Who did factorize it, then? How, and where, was the computation performed?