Computers Ltd.: What They Really Can’t Do (Popular Science) by David Harel (PDF)

Description

The computer has been hailed as the greatest innovation of the 20th century, and there is no denying that these technological marvels have dramatically changed our everyday lives. They can fly airplanes and spaceships, route millions of phone calls simultaneously, and play chess with theworld’s greatest players. But how limitless is the future for the computer? Will computers one day be truly intelligent, make medical diagnoses, run companies, compose music, and fall in love? In Computers Ltd., David Harel, the best-selling author of Algorithmics, illuminates one of the most fundamental yet under-reported facets of computers–their inherent limitations. Looking only at the bad news that is proven, discussing limitations that no amounts of hardware, software,talent, or resources can overcome, the book presents a disturbing and provocative view of computing at the start of the 21st century. Harel takes us on a fascinating tour that touches on everything from tiling problems and monkey puzzles to Monte Carlo algorithms and quantum computing, showing justhow far from perfect computers are, while shattering some of the many claims made for these machines. He concludes that though we may strive for bigger and better things in computing, we need to be realistic: computers are not omnipotent–far from it. Their limits are real and here to stay. Based on hard facts, mathematically proven and indisputable, Computers Ltd. offers a vividly written and often amusing look at the shape of the future.

User’s Reviews

Editorial Reviews: Review `Computers Ltd is a gripping book’ Cern Courier`a clear and friendly book’ The Guardian`Review from previous edition This book is a veritable tour de force. Harel writes with uncommon verve, clarity, and imagination . . . This is science writing at its best.’ Times Higher Education Supplement`This is the book I would most like to have written.’ Prof. Darrell Ince, Open University`Thank heavens . . . for David Harel’s book on the theoretical limitations of computers . . . the insights Computers Ltd. provides are of an unusually enduring and worthwhile nature.’ The Economist, 30 Sept. 2000`The best short introduction to the things that computers can, can’t, might, and could, eventually, do.’ John D. Barrow, Professor of Mathematical Sciences, Cambridge University, and author of ‘Impossibility’ and the forthcoming ‘Book of Nothing’`An enlightening and entertaining explanation, written by a profound computer scientist and master expositor. A must read for inquisitive minds.’ Michael Rabin, Professor of Computer Science, Harvard University About the Author David Harel is William Sussman Professor of Mathematics at The Weizmann Institute of Science, in Israel. One of the world’s leading computer scientists, he is the author of the critically acclaimed Algorithmics, which has sold more than 100,000 copies worldwide.

Reviews from Amazon users which were colected at the time this book was published on the website:

⭐David Harel is a computer scientist at the Weizmann Institute of Science in Israel; he was previously Dean of the Faculty of Mathematics and Computer Science at the Institute.He wrote in the Preamble to this 2000 book, “Of course, computers are incredible. They are without doubt the most important invention of the 20th century, having dramatically and irrevocably changed the way we live, and mostly for the better. But that is the good news… This book concentrates on the … negative side of things. Computers are expensive… programming them is laborious and using them can be difficult… they err; they crash; they contract viruses… But it is not these kinds of bad news that concern us here. The goal of the book is to explain and illustrate one of the most important and fundamental facets of the world of computing—its inherent limitations… [This book] concentrates on bad news that is proven, lasting, and robust, concerning problems that computers are simply not able to solve, regardless of our hardware, software, talents, or patience.” (Pg. vii-viii)He summarizes, “We have learned that the world of algorithmic/computational problems is divided into the computable, or decidable, vs. the noncomputable, or undecidable, and that among themselves the problems in the latter class exhibit various degrees of hardness. We have also see that these facts are extremely robust and lasting… So our hopes for computer omnipotence are shattered. We now know that not all algorithmic problems are solvable by computers, even with unlimited access to resources like time and memory space.” (Pg. 58)He points out, “there is a certain mismatch between existing parallel algorithms and the parallel computers that have been built to run them… the theory of parallel algorithms has yet to catch up with what the available hardware IS able to do. In the realm of quantum computation the situation is less symmetric. We have at our disposal some really nice quantum algorithms, but no machines whatsoever to run them on… there are severe technical problems around the actual building of a quantum computer. First, experimental physicists have not managed to be able to put even a small number of qubits (say, 20) together and control them in some reasonable way. The difficulties seem beyond present-day laboratory techniques… The quantum behavior of anything surrounding a quantum computer… can mess up the delicate setup of constructive and destructive interference within the quantum computation… The computer thus has to be relentlessly isolated from its environment. But it also has to read inputs and produce an output, and its computational process might have to be controlled by some external elements. Somehow, these contradictory requirements have to be reconciled.” (Pg. 151-153)He notes, “The knowledge representation problem becomes particularly acute when we consider LEARNING and PLANNING… The ability to plan is another intelligent skill. Some sophisticated mobile robots … are capable of planning a sequence of movements that will take them to their destination… Do they simply carry out a search through all possibilities, or do they utilize more subtle knowledge that enables them to look ahead, so to speak, and really plan with the goal in mind? Again, broader domains make things much harder… Way too little is known about how we ourselves deal with these tasks, and as a result we are very far from being able to teach them to a computer, even with the aid of learning mechanisms such as neural nets.” (Pg. 209-210)Harel’s explanations of how programming actually WORKS are helpful (if perhaps sometimes going into more detail than is necessary). This book will be of keen interest to those skeptical about Artificial Intelligence, and related topics.

⭐The is a good introductory book into the limits of computation. The book introduces the major concepts and vocabulary in a very easy to understand way. However that is the limit to this book on limits. If you are looking for non-technical information, then this may well be the book for you.If you are looking for proofs, answers to your homwork problems, or rigor, you will be disappointed. The author states many conjectures few have proofs. From the conjectures he uses easily understood arguments to make his points. The conjectors are in fact true, but you will have to look elsewhere to find proofs.The reasons I gave 4 stars instead of 5 are twofold. Although the book is pretty good, the writing seems a bit quirky at times. I would have liked to have seen a bit more rigor. Although I can understand wanting the book to be as simple as possible, but many of the proofs are not very difficult and could have been included (for example the halting problem).

⭐The January 1990 AT&T telephone network crash and the June 1996 inflight explosion of an Ariane 5 rocket were caused by software failures. These two citations by Harel are two examples of incorrect computer programming that should have been avoidable. With our industrial economy relying to an ever-greater extent on computers for essential functions, the importance of software reliability stands in stark relief.Harel’s third example, that of a 107 year old woman who was mailed registration paperwork for first grade, highlights that even our system of social organization is being dependent on competently run computer networks. Now, this may not be so dramatic as network or rocket crashes, but multiplied by our burgeoning population, it illustrates the fiscal nibbling that computer errors exact on our public budgets.Thus Harel, having established the stakes (not at the outset, unfortunately, but near the end of Chapter 1), takes up the technical issues having to do with correctness of computation. The book begins with a discussion of the algorithm: the program, inputs, instances, programming languages, and termination. Then in the next chapters he goes on to problems that, even theoretically, defy solution by any means. He describes the Church-Turing Thesis having to do with “effective computability”, and the Halting Problem and Rice’s Theorem, “No algorithm can decide any nontrivial property of computations.Even the problems that are solvable in theory just take too much time or machine resources to be economically worthwhile. These are the subject of Ch. 3. Chapter 4 has to do with NP-complete problems: decidable but not known to be tractable (worthwhile). In other words, you know that you can know, but you don’t know!Ch. 5 takes up algorithmic parallelism (mainly), which offers hope. Also touches on randomization, quantum computing, and molecular computing. Ch. 6 takes up cryptography, leading up to the RSA algorithm, and the zero knowledge proofs.The last chapter takes up the notion of “artificial intelligence”, the Turing test, Eliza, searching strategies, etc.It also touches on issues not unlike those demonstrated by the recent IBM Watson project: “The difficulty is rooted in the observation that human knowledge does not consist merely of a large collection of facts. It is not only the sheer number and volume of facts that is overwhelming…but, to a much larger extent, their interrelationships and dynamics…a human’s knowledge base is incredibly complex, and works in ways that are still far beyond our comprehension.” Fact is, even now, after Watson, we STILL don’t understand how a human knowledge base works, because Watson is not a human and does not employ human search strategies. Despite the media hype that IBM has been trying to work up on the Sunday morning news shows, Watson is still just a souped-up search engine with an English-language front end. Interesting and potentially useful, but no breakthrough.Seems funny, or perhaps not, that this topic is taken up in the same chapter discussing the Turing test. Watson may produce results competitive with those of humans, but it works in a completely different way — machine learning. Which means, basically, it is still a rules-based system, but it makes up new rules and modified rules as it operates. Human cognitive machinery is not rules-based. Turing says you can ignore the underlying mechanism; the only way you have to compare a human and a machine is by the results alone. It is a computer equivilant to the behaviorist perspective in psychology: all that matters is what you can see in front of you. Again, nothing new here, this has been apparent since the days of Eliza.The book is rather theory-oriented but still educational. When Harel cited those three real-world instances I thought the text would be more practically oriented; on this score I was disappointed. But still it’s a worthwhile read.

⭐As expected.

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