The fabric of reality

The fabric of reality by David Deutsch is certainly one of the most delightful books I have read. Now I would rate a good popular science book along the axes of being informative, readable, comprehensible. Very few would qualify as being delightful, so let me try to say why this one does.

A popular science book is, in general,  intended for the person who is curious about some field of science, but lacks the time and/or brainpower to undertake a thorough study.  While by design it can't get into the details, the good ones provide an understanding that is not wholly superficial. Generally they talk about a specific area of science. The fabric of  reality distinguishes itself, firstly, by not being about any specific area of science as such, but about the worldview that emerges when we take our best theories seriously, and treat them together. The theories in question are, namely, quantum physics, evolution by natural selection, theory of computation and Popper's theory of knowledge.

Is it possible for one person to understand everything that is understood? The book opens with this question and Deutsch answers this in the affirmative. Knowing all the facts is clearly  impossible, but understanding comes from explanations. The deeper the theory, the more it explains and you understand more even while having to know less. Science is fundamentally about explanations. This last is an important point, and (at least) I have not seen it made with such force and eloquence before.

Quantum physics has pretty good coverage of its own in the popular science category of course. As far as I can tell though, most of it makes a virtue of the counter intuitiveness of the quantum, which befuddles the nonexpert. The many worlds interpretation of quantum mechanics makes the same predictions as the standard Copenhagen interpretation (which is often implicit in the popular accounts), but Deutsch argues powerfully that it embodies a better explanation. Part of the argument comes from quantum computing, especially Shor's algorithm for factoring. Factoring is an intractable task with currently known classical algorithms, but quantum computers can factor in polynomial time using Shor's algorithm. Deutsch asks, where does this factoring take place, if not in the multiverse? I know that the case for choosing one interpretation over another is not settled among the experts, but (as someone whose entire knowledge in this area comes from reading a few popular science books), I can say at least that I find Deutsch's explanation to be much more comprehensible than the alternative. In other words, I now believe in parallel universes :-) [I plan to revisit this bit some time later and see if I still believe in them. I also plan to read more on this topic]. Another related point is whether we should believe in parallel universes though they are not directly perceptible except for interference phenomenon in special situations. To this end, Deutsch develops a criteria for reality, viz, if something behaves in a complex and autonomous way needing independent explanation, it is real. And so are the parallel universes. Another important point, but not addressed elsewhere.

Inductivism is a theory of knowledge, which says that theories come by way of generalizing observations and are justified when their predictions are confirmed (more times the better). Deutsch points out that no amount of confirmation can give sureshot confidence, and theories in general come by way of good explanations and not from generalizing observations. In Popper's scheme, problem solving within the context of existing theories and their perceived deficiencies is of the essence. There is no ultimate source of justification for a theory (in the form of a principle of induction), but we are justified in acting on them because their rivals have been refuted by rational argument and/or experimental failure. This does not mean a better theory would not appear tomorrow. Parts of the book dealing with epistemology were a major source of the delight that I alluded to earlier.

There are of course, so many other things worth mentioning. Real quickly; how replicators survive by embodying true knowledge about their niches and how their  adaptation means their structures would be identical across the multiverse; how the concept of a flow of time does not make sense, but that of free will does and that too without letting go of determinism; what are the limits of virtual reality and why it is fundamentally important (instead of being just a new form of entertainment); how Turing was mistaken in thinking he 'undetstood paper' (as Feynman once put it); is time travel possible and if so, are paradoxes possible; what is the relation between mathematical existence and mathematical proof; and so on and on. But I see this post is already quite long and my point already quite clear.

There are very few books which made me want to reread them as soon they were finished, this one is one of those few  (I ended up ordering Deutsch's Beginning of Infinity in this case). One reviewer has compared Deutsch to Russell as a stylist and I could not agree more. As I said after finishing Russell's autobiography, it made everything else seem schoolboyish. This one, to a lower degree of course, certainly did too.