Book Summary & Highlights: The Fabric of Reality: The Science of Parallel Universes - and Its Implications By David Deutsch

Book Summary & Highlights: The Fabric of Reality: The Science of Parallel Universes - and Its Implications By David Deutsch

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Pub Date:

1998

Amazon Summary

For David Deutsch, a young physicist of unusual originality, quantum theory contains our most fundamental knowledge of the physical world. Taken literally, it implies that there are many universes “parallel” to the one we see around us. This multiplicity of universes, according to Deutsch, turns out to be the key to achieving a new worldview, one which synthesizes the theories of evolution, computation, and knowledge with quantum physics. Considered jointly, these four strands of explanation reveal a unified fabric of reality that is both objective and comprehensible, the subject of this daring, challenging book.

The Fabric of Reality explains and connects many topics at the leading edge of current research and thinking, such as quantum computers (which work by effectively collaborating with their counterparts in other universes), the physics of time travel, the comprehensibility of nature and the physical limits of virtual reality, the significance of human life, and the ultimate fate of the universe. Here, for scientist and layperson alike, for philosopher, science-fiction reader, biologist, and computer expert, is a startlingly complete and rational synthesis of disciplines, and a new, optimistic message about existence.

David Deutsch Summary

A new, integrated and rational world view based on four main strands:

  • Quantum physics and its many-universes interpretation
  • The theory of evolution (Darwin/Dawkins)
  • The theory of computation (quantum computation)
  • The theory of knowledge (Karl Popper), explanation and understanding

The Fabric of Reality presents a startlingly integrated, rational and optimistic world view – the result of taking seriously the deepest ideas of modern science and the philosophy of science. The four main strands of explanation involved in this synthesisare quantum physics and the theories of evolution computation, and knowledge. These strands may seem unrelated, yet this book shows that they are so closely intertwined that we cannot properly understand any one of them without reference to the other three. Considered in isolation, each of them has explanatory gaps which have inhibited people from accepting them as being literally true. But considered jointly, they reveal a unified fabric of reality that is objective and comprehensible, and in which human actions and ideas play essential roles.

The most profound of the four strands is quantum theory, which contains our most fundamental knowledge of the physical world. Taken literally, it implies that there are many universes ‘parallel’ to the one we see around us, and that they are detectable through the astonishing phenomenon of quantum interference. The multiplicity of universes turns out to be the key to the unification of the four strands. For example, both the growth of scientific knowledge and the evolution of biological adaptations are best understood as multi-universe phenomena: normally, universes tend to become less alike with time, and the only two known processes capable of making them more alike are biological evolution and human thought.

About Author: David Deutsch

David Deutsch is one of the top physicist and physicist explainers in the world. Read more about David Deutsch...

Contents

1. The Theory Of Everything

Our best explanations are getting deeper and broader.

Terminology

Epistemology. The study of the nature of knowledge and the processes that create it.

Explanation (roughly). A statement about the nature of things and the reasons for things.

Instrumentalism. The view that the purpose of a scientific theory is to predict the outcomes of experiments.

Positivism. An extreme form of instrumentalism which holds that all statements other than those describing or predicting observations are meaningless. (This view is itself meaningless according to its own criterion.)

Reductive. A reductive explanation is one that works by analysing things into lower-level components. reductionism The view that scientific explanations are inherently reductive.

Holism. The idea that the only legitimate explanations are in terms of higher-level systems; the opposite of reductionism.

Emergence. An emergent phenomenon is one (such as life, thought or computation) about which there are comprehensible facts or explanations that are not simply deducible from lower-level theories, but which may be explicable or predictable by higher-level theories referring directly to that phenomenon.

Summary

Scientific knowledge, like all human knowledge, consists primarily of explanations. Mere facts can be looked up, and predictions are important only for conducting crucial experimental tests to discriminate between competing scientific theories that have already passed the test of being good explanations. As new theories supersede old ones, our knowledge is becoming both broader (as new subjects are created) and deeper (as our fundamental theories explain more, and become more general). Depth is winning. Thus we are not heading away from a state in which one person could understand everything that was understood, but towards it. Our deepest theories are becoming so integrated with one another that they can be understood only jointly, as a single theory of a unified fabric of reality. This Theory of Everything has a far wider scope than the ‘theory of everything’ that elementary particle physicists are seeking, because the fabric of reality does not consist only of reductionist ingredients such as space, time and subatomic particles, but also, for example, of life, thought and computation.

The four main strands of explanation which may constitute the first Theory of Everything are:

  • Quantum physics
  • Epistemology
  • The theory of computation
  • The theory of evolution

2. Shadows

How we know that there are parallel universes.

Summary

In interference experiments there can be places in a shadow-pattern that go dark when new openings are made in the barrier casting the shadow. This remains true even when the experiment is performed with individual particles. A chain of reasoning based on this fact rules out the possibility that the universe we see around us constitutes the whole of reality. In fact the whole of physical reality, the multiverse, contains vast numbers of parallel universes.

3. Problem-Solving

Conjecture, criticism and refutation, but not induction

In fundamental areas of science, observations of ever smaller, more subtle effects are driving us to ever more momentous conclusions about the nature of reality.

Yet these conclusions cannot be deduced by pure logic from the observations. So what makes them compelling? This is the ‘problem of induction’.

According to inductivism, scientific theories are discovered by extrapolating the results of observations, and justified when corroborating observations are obtained. In fact, inductive reasoning is invalid, and it is impossible to extrapolate observations unless one already has an explanatory framework for them.

But the refutation of inductivism, and also the real solution of the problem of induction, depends on recognizing that science is a process not of deriving predictions from observations, but of finding explanations. We seek explanations when we encounter a problem with existing ones. We then embark on a problem-solving process. New explanatory theories begin as unjustified conjectures, which are criticized and compared according to the criteria inherent in the problem. Those that fail to survive this criticism are abandoned. The survivors become the new prevailing theories, some of which are themselves problematic and so lead us to seek even better explanations. The whole process resembles biological evolution.

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?

4. Criteria for Reality

Although solipsism and related doctrines are logically self-consistent, they can be comprehensively refuted simply by taking them seriously as explanations. Although they all claim to be simplified world-views, such an analysis shows them to be indefensible over-elaborations of realism. Real entities behave in a complex and autonomous way, which can be taken as the criterion for reality: if something ‘kicks back’, it exists. Scientific reasoning, which uses observation not as a basis for extrapolation but to distinguish between otherwise equally good explanations, can give us genuine knowledge about reality.

5. Virtual Reality

Virtual reality is not just a technology in which computers simulate the behaviour of physical environments. The fact that virtual reality is possible is an important fact about the fabric of reality. It is the basis not only of computation, but of human imagination and external experience, science and mathematics, art and fiction.

What are the ultimate limits — the full scope — of virtual reality (and hence of computation, science, imagination and the rest)? In the next chapter we shall see that in one respect the scope of virtual reality is unlimited, while in another it is drastically circumscribed.

6. Universality and the Limits Of Computation (Computation)

The diagonal argument shows that the overwhelming majority of logically possible environments cannot be rendered in virtual reality. I have called them Cantgotu environments. There is nevertheless a comprehensive self-similarity in physical reality that is expressed in the Turing principle: it is possible to build a virtual-reality generator whose repertoire includes every physically possible environment. So a single, buildable physical object can mimic all the behaviours and responses of any other physically possible object or process. This is what makes reality comprehensible. It also makes possible the evolution of living organisms. However, before I discuss the theory of evolution, the fourth strand of explanation of the fabric of reality, I must make a brief excursion into epistemology.

7. A Conversation About Justification (Epistemology)

8. The Significance Of Life (Evolution)

9. Quantum Computers

The laws of physics permit computers that can render every physically possible environment without using impractically large resources. So universal computation is not merely possible, as required by the Turing principle, it is also tractable. Quantum phenomena may involve vast numbers of parallel universes and therefore may not be capable of being efficiently simulated within one universe. However, this strong form of universality still holds because quantum computers can efficiently render every physically possible quantum environment, even when vast numbers of universes are interacting. Quantum computers can also efficiently solve certain mathematical problems, such as factorization, which are classically intractable, and can implement types of cryptography which are classically impossible. Quantum computation is a qualitatively new way of harnessing nature.

The next chapter is likely to provoke many mathematicians. This can’t be helped. Mathematics is not what they think it is. (Readers who are unfamiliar with traditional assumptions about the certainty of mathematical knowledge may consider the chapter’s main conclusion — that our knowledge of mathematical truth depends on, and is no more reliable than, our knowledge of the physical world — to be obvious. Such readers may prefer to skim this chapter and hurry on to the discussion of time in Chapter 11.)

10. The Nature Of Mathematics

Abstract entities that are complex and autonomous exist objectively and are part of the fabric of reality. There exist logically necessary truths about these entities, and these comprise the subject-matter of mathematics.

However, such truths cannot be known with certainty. Proofs do not confer certainty upon their conclusions. The validity of a particular form of proof depends on the truth of our theories of the behaviour of the objects with which we perform the proof. Therefore mathematical knowledge is inherently derivative, depending entirely on our knowledge of physics. The comprehensible mathematical truths are precisely the infinitesimal minority which can be rendered in virtual reality. But the incomprehensible mathematical entities (e.g. Cantgotu environments) exist too, because they appear inextricably in our explanations of the comprehensible ones. I have said that computation always was a quantum concept, because classical physics was incompatible with the intuitions that formed the basis of the classical theory of computation. The same thing is true of time. Millennia before the discovery of quantum theory, time was the first quantum concept.

11. Time: The First Quantum Concept

Time does not flow.

Other times are just special cases of other universes. Time travel may or may not be feasible. But we already have a reasonably good theoretical understanding of what it would be like if it were, an understanding that involves all four strands.

12. Time Travel

Time travel may or may not be achieved one day, but it is not paradoxical. If one travels into the past one retains one’s normal freedom of action, but in general ends up in the past of a different universe. The study of time travel is an area of theoretical study in which all four of my main strands are significant: quantum mechanics, with its parallel universes and the quantum concept of time; the theory of computation, because of the connections between virtual reality and time travel, and because the distinctive features of time travel can be analysed as new modes of computation; and epistemology and the theory of evolution, because of the constraints they impose on how knowledge can come into existence.

Not only are the four strands related as part of the fabric of reality, there are also remarkable parallels between the four fields of knowledge as such. All four basic theories have the unusual status of being simultaneously accepted and rejected, relied upon and disbelieved, by most people working in those fields.

13. The Four Strands

The intellectual histories of the fundamental theories of the four strands contain remarkable parallels. All four have been:

  • simultaneously accepted (for use in practice)
  • ignored (as explanations of reality).

One reason for this is that, taken individually, each of the four theories…

  • Has explanatory gaps
  • Seems cold and pessimistic.

To base a world-view on any of them individually is, in a generalized sense, reductionist. But when they are taken together as a unified explanation of the fabric of reality, this is no longer so.

Highlights

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“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.”
“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.”
“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.”
“Existimos en múltiples versiones en universos denominados «momentos».”
“El tiempo no transcurre. Otros tiempos son, simplemente, casos especiales de otros universos.”
“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.)”
“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.”
“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.”
“They are also about coherence, elegance and simplicity, as opposed to arbitrariness and complexity, though none of those things is easy to define either.”
“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.”
“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.”
“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.”
“Not only is there constant backtracking, but the many subproblems all remain simultaneously active and are addressed opportunistically.”
“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?”
“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.”