The Fabric of Reality 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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“They are also about coherence, elegance and simplicity, as opposed to arbitrariness and complexity, though none of those things is easy to define either.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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.)”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Existimos en múltiples versiones en universos denominados «momentos».”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--And Its Implications

“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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“El tiempo no transcurre. Otros tiempos son, simplemente, casos especiales de otros universos.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Not only is there constant backtracking, but the many subproblems all remain simultaneously active and are addressed opportunistically.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“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?”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Again we were too parochial, and were led to the false conclusion that knowledge-bearing entities can be physically identical to non-knowledge-bearing ones; and this in turn cast doubt on the fundamental status of knowledge. But now we have come almost full circle. We can see that the ancient idea that living matter has special physical properties was almost true: it is not living matter but knowledge-bearing matter that is physically special. Within one universe it looks irregular; across universes it has a regular structure, like a crystal in the multiverse.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“If it turns out that all this time we have merely been studying the programming of a cosmic planetarium, then that would merely mean that we have been studying a smaller portion of reality than we thought. So what? Such things have happened many times in the history of science, as our horizons have expanded beyond the Earth to include the solar system, our Galaxy, other galaxies, clusters of galaxies and so on, and, of course, parallel universes.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Shoddy explanations that yield correct predictions are two a penny, as UFO enthusiasts, conspiracy-theorists and pseudo-scientists of every variety should (but never do) bear in mind.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“But Darwin was able to wonder how laws of nature that did not mention elephants could nevertheless produce them,”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Being able to predict things or to describe them, however accurately, is not at all the same thing as understanding them. Predictions and descriptions in physics are often expressed as mathematical formulae. Suppose that I memorize the formula from which I could, if I had the time and the inclination, calculate any planetary position that has been recorded in the astronomical archives. What exactly have I gained, compared with memorizing those archives directly? The formula is easier to remember – but then, looking a number up in the archives may be even easier than calculating it from the formula. The real advantage of the formula is that it can be used in an infinity of cases beyond the archived data, for instance to predict the results of future observations.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“evidence. That is indeed one aspect of his discovery: scientific reasoning is reliable, not in the sense that it certifies that any particular theory will survive unchanged, even until tomorrow, but in the sense that we are right to rely on it. For we are right to seek solutions to problems rather than sources of ultimate justification. Observational evidence is indeed evidence, not in the sense that any theory can be deduced, induced or in any other way inferred from it, but in the sense that it can constitute a genuine reason for preferring one theory to another.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“There is a continual turnover of theories as they are altered or replaced by new ones. So all the theories are being subjected to variation and selection, according to criteria which are themselves subject to variation and selection. The whole 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. Variants of theories, like genetic mutations, are continually being created, and less successful variants become extinct when more successful variants take over. ‘Success’ is the ability to survive repeatedly under the selective pressures – criticism – brought to bear in that niche, and the criteria for that criticism depend partly on the physical characteristics of the niche and partly on the attributes of other genes and species (i.e. other ideas) that are already present there.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“Whereas an incorrect prediction automatically renders the underlying explanation unsatisfactory, a correct prediction says nothing at all about the underlying explanation. Shoddy explanations that yield correct predictions are two a penny, as UFO enthusiasts, conspiracy-theorists and pseudo-scientists of every variety should (but never do) bear in mind.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“A good explanation may make good predictions about the future, but the one thing that no explanation can even begin to predict is the content or quality of its own future rivals.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“In science the object of the exercise is not to find a theory that will, or is likely to, be deemed true for ever; it is to find the best theory available now, and if possible to improve on all available theories.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“even mere predictions can never be justified by observational evidence, as Bertrand Russell illustrated in his story of the chicken. (To avoid any possible misunderstanding, let me stress that this was a metaphorical, anthropomorphic chicken, representing a human being trying to understand the regularities of the universe.) The chicken noticed that the farmer came every day to feed it. It predicted that the farmer would continue to bring food every day. Inductivists think that the chicken had ‘extrapolated’ its observations into a theory, and that each feeding time added justification to that theory. Then one day the farmer came and wrung the chicken’s neck. The disappointment experienced by Russell’s chicken has also been experienced by trillions of other chickens. This inductively justifies the conclusion that induction cannot justify any conclusions!”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“To those who would prefer reality to have a more prosaic structure, it may seem somehow out of proportion – unfair, even – that such momentous consequences can flow from the fact that a tiny spot of light on a screen should be here rather than there.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“If knowledge is to continue its open-ended growth, and if we are nevertheless heading towards a state in which one person could understand everything that is understood, then the depth of our theories must continue to grow fast enough to make this possible. That can happen only if the fabric of reality is itself highly unified, so that more and more of it can become understood as our knowledge grows. If that happens, then eventually our theories will become so general, deep and integrated with one another that they will effectively become a single theory of a unified fabric of reality. This theory will still not explain every aspect of reality: that is unattainable. But it will encompass all known explanations, and will apply to the whole fabric of reality in so far as it is understood. Whereas all previous theories related to particular subjects, this will be a theory of all subjects: a Theory of Everything. It will not, of course, be the last such theory, only the first. In science we take it for granted that even our best theories are bound to be imperfect and problematic in some ways, and we expect them to be superseded in due course by deeper, more accurate theories. Such progress is not brought to a halt when we discover a universal theory.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“Being able to predict things or to describe them, however accurately, is not at all the same thing as understanding them.”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Thus we acquire ever more knowledge of reality by solving problems and finding better explanations. But when all is said and done, problems and explanations are located within the human mind, which owes its reasoning power to a fallible brain, and its supply of information to fallible senses. What, then, entitles a human mind to draw conclusions about objective, external reality from its own purely subjective experience and reason?”
― David Deutsch, The Fabric of Reality: The Science of Parallel Universes--and Its Implications

“Quantum theory is, as I have said, one such theory. But the other three main strands of explanation through which we seek to understand the fabric of reality are all ‘high level’ from the point of view of quantum physics. They are the theory of evolution (primarily the evolution of living organisms), epistemology (the theory of knowledge) and the theory of computation (about computers and what they can and cannot, in principle, compute).”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything

“The fabric of reality does not consist only of reductionist ingredients like space, time and subatomic particles, but also of life, thought, computation and the other things to which those explanations refer.”
― David Deutsch, The Fabric of Reality: Towards a Theory of Everything