Programming the Universe: A Quantum Computer Scientist Takes on the Cosmos

What would you think of a professor who starts his course this way: " First you ask questions and I'll try to answer them. Second, if you don't ask questions, I'll ask you questions. Third, if you don't answer my questions, I'll tell you something I think you ought to know. Any questions? " And then, when there are no questions, he throws in his own: "What is information?".Well, this is, apparently, the style of professor Seth Lloyd and I would certainly enjoy to be in his class and , by the way, his question stimulated my brain , so my answer would be: "Information implies some kind of `language', the elements of language being the signs, the syntactic rules and the interpretation (the meaning). Information normally goes from an emitter to a receiver through some channel. Information can also be processed and stored."So what is this book about? Well, the standard paradigm of the universe is mechanistic and energy is the most important quantity. Lloyd advocates a new complementary paradigm: the universe is a machine that computes and the two primary quantities are energy and information. A phrase summarizes the main idea of the book: "It from bit "or , rather, "It from qubit". The new paradigm solves the problem of the natural emergency of complexity (although Darwin already partly tackled this problem) and does away the need of the God Watchmaker. It all starts from nothing, quantum mechanics provides the random fluctuations and the computer gets self started (according to Lloyd, "Quantum mechanics, unlike classical mechanics, can create information out of nothing"). Yes, there is a new version of the famous story about monkeys (unsuccessfully) trying to type Hamlet or other Shakespeare works with typewriters (by the way, a simulation has only managed to type the first 24 letters of Henry IV, Part 2 after trillions and trillions of monkey-years). The new version is to use computers instead of typewriters and interpret the output as computer programs in one of the standard languages. Yes, there are relatively short programs that produce astounding outputs.So the book, to explain all this starts to talk about computers in one of the most concise and clear ways I have ever seen . It goes on to describe the universe as a computer, one that computes itself, that is, its dynamical evolution. But since the universe is a quantum computer, quantum mechanics needs to be discussed, in particular the beautiful double slit experiment (an excellent video can be seen at [...] ) and other weird aspects of QM such as entanglement, spooky action at distance, the different interpretations of QM, etc. Well the lay reader will find some difficulties in these chapters about quantum mechanics and quantum computers, but the effort is worthwhile. Quantum computers pose a threat to Internet security, because using Schor's algorithm, a quantum computer could easily factorize 400 digit numbers. However, the technical difficulties in building but the most elementary quantum computers (to insulate them to avoid decoherence) make this threat still a chimera (only a number such as 15 has been factorized by a quantum computer). However, quantum computers have done simulations that no classical computer could achieve.On the side, you will get some philosophical, physical and mathematical servings. For example, the relation of Gödel's theorem , or the related Turing's halting problem, to free will. "Rationality combines with self-reference to make our actions intrinsically paradoxical and uncertain", claims Lloyd. You will also learn about a fourth road to quantum gravity via quantum computation and some notions of the complexity theory of Chaitin and Bennett.To sum up, a good book, with some easy chapters and some more difficult ones.

As if quantum theory wasn't enough to stretch the limits of comprehension, now information theory is emerging and stretching those limits even further.Black holes acting as incredibly accurate quantum computers? That's just a start. How about the universe itself being a computer?This is the intriguing assertion of Seth Lloyd in his new book, Programming the Universe: A Quantum Computer Scientist Takes On the Cosmos."The Universe is a quantum computer. ...What does the universe compute? It computes itself. The universe computes its own behavior. As soon as the universe began, it began computing."The idea, in various forms, has been around for awhile. Ed Fredkin has been developing the idea since the 60's. Though his website is a bit technical for the average reader, a superb article by Robert Wright in The Atlantic Monthly captures both the essential ideas and the man himself.According to his theory of digital physics, information is more fundamental than matter and energy. He believes that atoms, electrons, and quarks consist ultimately of bits--binary units of information, like those that are the currency of computation in a personal computer or a pocket calculator. And he believes that the behavior of those bits, and thus of the entire universe, is governed by a single programming rule. This rule, Fredkin says, is something fairly simple, something vastly less arcane than the mathematical constructs that conventional physicists use to explain the dynamics of physical reality. Yet through ceaseless repetition--by tirelessly taking information it has just transformed and transforming it further--it has generated pervasive complexity. Fredkin calls this rule, with discernible reverence, "the cause and prime mover of everything."This "prime mover of everything" is a class of computer programs known as cellular automata which were invented by John von Neumann in the 1950s. More recently Stephen Wolfram has explored cellular automata in great detail in his monumental work, A New Kind of Science, in which he sees this form of analysis and understanding as ushering in a new method of doing science. The cellular automaton is a lattice of cells, which can have a finite number of states. These states result from rules which advance in discrete steps and which simultaneously update the lattice. Wolfram explored hundreds of these rules through computer analysis.So the universe could itself be a process of working out these computational processes according to some rule. And if so, then our picture of the nature of reality changes dramatically:Fredkin believes that automata will more faithfully mirror reality as they are applied to its more fundamental levels and the rules needed to model the motion of molecules, atoms, electrons, and quarks are uncovered. And he believes that at the most fundamental level (whatever that turns out to be) the automaton will describe the physical world with perfect precision, because at that level the universe is a cellular automaton, in three dimensions--a crystalline lattice of interacting logic units, each one "deciding" zillions of times per second whether it will be off or on at the next point in time. The information thus produced, Fredkin says, is the fabric of reality, the stuff of which matter and energy are made. An electron, in Fredkin's universe, is nothing more than a pattern of information, and an orbiting electron is nothing more than that pattern moving.This universe is no longer the continuous process that our perceptual system sees. Rather it is a discrete process of events. The physicist John Wheeler entitled an article on this understanding as "It from Bit"-a phrase that has become a popular way of encapsulating the idea.Back to Seth Lloyd. He is working at this interface of computer science and physics-- what Robert Wright calls the "twilight zone of modern science". He surveys the basicprinciples of quantum computing, exploring questions such as: How much information is there in the universe? How much was present at the Big Bang? Can we re-create it on a giant quantum computer? How is information related to entropy? He answers these questions with surprising clarity for ideas that are so foreign to our everyday understanding.The strength in Lloyd's book is the presentation of the core ideas of quantum computing. Those of a more philosophical bent might have wished for more speculation on the implications of his model. However, he does end his book with a "Personal Note: The Consolation of Information," in which he describes the tragic death of his teacher and friend Heinz Pagels. They were hiking together in the Colorado mountains when Heinz slipped and fell. After the rescue efforts, he was left with trying to make sense of what happened. He concludes his book with this reflection:Heinz's body and brain are gone. The information his cells processed is wrapped up in the Earth's slow process. He has lost consciousness, thought, and action. But we have not entirely lost him. While he lived, Heinz programmed his own piece of the universe. The resulting computation unfolds in us and around us: the vivid thoughts and outrageous behavior he impressed on us still flourish in our thoughts and behavior and have their own vivid and outrageous consequences. Heinz's piece of the universal computation goes on.

Do yourself a favor by purchasing this book. You may not understand a concept and start asking yourself questions, don't worry. The author will reveal the answer in the following sentence or paragraph. The author Seth Lloyd is a magician. He will roll you, the boulder uphill in comprehension, and you won't even realize It. The book unfolds as a journey but reads as a path dotted with treats of information and humor along the way.

Ho particolarmente apprezzato le disquisizioni sull'universo in termini di informazioni e computazione; per contro le argomentazioni mi sono parse talvolta slegate e non sorrette da una visione generale; il libro non ha utilità particolari se non quelle di arricchire la cultura generale informatica, inserendovi anche l'universo nella sua interezza; ne consiglio senz'altro la lettura a chi ha nel proprio curriculum elementi di informatica, ma anche a chi ne è totalmente sprovvisto, anche se per questi ultimi sarà più difficoltosa.

Es muy buen libro,Considero que para seguir y entende bien este libro de Seth LLoyd,es conveniente de disponer de algo de conocimientos respecto a los temas que se tratan. Al inicio de la lectura, uno podria pensar que el autor deberia haberse extendido algo mas, incluyendo graficos, figuras y algo de matematicas, pero cuando uno ya esta absorvido por el tema, comprende que el autor ha escogido el nivel y desarrollo adecuados, pues de lo contrario el libro hubiera tenido que ser bastante mas amplio y demasiado complicado, limitando en consaecuencia el acceso a mas publico.El libro toca basicamente todos los temas que ya se desprenden de su titulo: Computacion, computacion cuantica,sisitemas aleatorios, informacion e interaccion entre aleatoriedad y posibilidad de desarrollo efectivo y todo ello a nivel cosmico.Un gran libro que es util para una amplia variedad de personas, que de buen seguro que les hara pensar.Es de los libros que deben leerse

Seth Lloyd is one of the founders of Quantum Computing and applications in Quantum Machine Learning and number of other areas in Quantum Computing. He has written seminal research papers in this extremely exciting and currently very important area not only in pure quantum physics research, but also applications in industry. So it is no wonder that the clarity with which he has explained the concepts of Quantum Computing are wonderful. I especially liked the part about entropy as information. Given that there is not a single mathematical equation in the book, explaining concepts in quantum mechanics and related areas, especially entanglement is a real challenge which Seth has done very beautifully with simple analogies. Overall a wonderful book for those interested in getting into quantum computing seriously and would like an intuitive (non-mathematical) view of things.

John Archibald Wheeler war einer der herausragenden Physiker, der die Theoretische Physik des 20. Jahrhunderts maßgeblich mit gestaltet hat, oft überraschte er mit ungewöhnlichen Ansätzen, dabei interessierte er sich letztlich für die „wirklich großen Fragen“ an die Natur (vgl. Science & Ultimate Reality). Eine dieser Fragen lautet 'it from bit?' – dazu regte Wheeler 2005 Seth Lloyd, Inhaber des Nam Pyo Suh Lehrstuhls am MIT, an, einen Vortrag am Santa Fe Institute for sudy of complex systems zu halten, um seine Ideen zum Universum als Quantencomputer, der sich selbst berechnet, vor zustellen.Seth Lloyd, dem es 1993 als einer der ersten gelungen war, ein funktionsfähiges Modell eine Quantencomputers zu bauen, nahm den Vortrag zum Anlass, um seine kontroversen Thesen allgemein verständlich in Form des vorliegenden Buches herauszugeben. In zehn Kapiteln entwickelt der Autor seine Argumente, inwiefern die physikalische Realität auf Informationsverarbeitung beruht.Bereits die klassische Thermodynamik lieferte erste Anhaltspunkte: ein Maxwellscher Dämon, der Informationen über die 'Zustände' der Atome oder Moleküle eines Gases gewinnen kann, kann damit das 2. Gesetz der Thermodynamik 'verletzen' – insofern sind die Entropie des Gases und die Information, die im 'Gedächtnis' des Dämons gespeichert ist, miteinander verknüpft.Physikalische Systeme können logische Gatter wie AND, OR und NOT emulieren, das ist sowohl im Bereich der klassischen Mechanik (Billard Ball Computer) als auch quantenmechanisch möglich; darauf stießen Fredkin, Toffoli u.a. bei der Untersuchung der physikalischen Grenzen von Computern; kombiniert man nun genügend viele solcher Quantum Gates – erhält man einen Quantencomputer.Computer, hinreichender Mächtigkeit, besitzen eine wichtige Eigenschaft – die Universalität, d.h. ein solcher Computer kann jeden anderen, gleichgültig welcher Bauart und Größe, allein mit Hilfe eines Programms (Software) emulieren. Darauf stieß bereits Alan Turing bei seiner Untersuchung von '.. comutable numbers'.(Das ist für Turing Maschinen eine durchaus überraschende Eigenschaft, denn d.h. eine bestimmte endliche Maschine kann jede andere, auch beliebig große, Maschine emulieren, allein auf Grund von Code auf dem Speicherband, worauf diese Turing Maschine ja auch nur lokal zugreifen – mit je einem Zeichen – kann.)Diese Ideen konnten auch auf Quantencomputer übertrage werden – genauer bewies Richard Feynman die Existenz von universellen Quanten Simulatoren, damit zeigt David Deutsch schließlich die Universalität von Quantencomputern. Nun ist auch das Universum ein Quantensystem, das durch Quantensysteme aus logischen Quanten Gates simuliert werden kann – insofern sind die Vorgänge im Universum durch die Operationen eine Quantencomputer beschreibbar.Aber inwiefern bietet diese Interpretation Vorteil gegenüber der traditionelle Sichtweise. Der Autor führt dazu im wesentlichen zwei Argumente an: zum einen hat er – anspielend auf Lee Smolins „Three Roads to Quantum Graviity“ – einen vierten Weg gefunden, die Raumzeit als Geflecht ein von Quantum Gates, die in diverser Weise mit 'Kabeln' verbunden sind, darzustellen; er erläutert, dass die Unabhängigkeit der logischen Operationen von der 'Einbettung' der Gatter in einen raumzeitlichen Untergrund, in natürlicher Weise zur Kovarianz des Ansatzes führt, und die Gültigkeit der Einsteinschen Gleichungen gezeigt werden kann. Das stützt die Hoffnung, dass diese Theorie sich zu einer PTOE (potential theory of everything) ausbauen lässt, wie Seth Lloyd es bescheiden nennt.Zum zweiten bietet die Hypothese vom 'rechnenden Universum' möglicherweise eine Erklärung dafür, wieso das Universum so komplex ist, obwohl sein Zustand unmittelbar nach dem Big Bang sehr homogen, symmetrisch und einfach war. Schon Boltzmann hat vermutet, dass Komplexität aus zufälligen Fluktuationen und einer Menge Zeit resultiert. Im Kontext des Computer Universums, entsprechen zufälligen Fluktuationen zufällig Bitstrings, nun kann aber der Quantencomputer diese als zufällige Programme interpretieren und 'ausführen'. Und in der Tat können Programme ,mit nur wenigen Dutzend Anweisen zum Beispiel Millionen Dezimalstellen von Pi ausgeben – somit ist die zufällige Entstehung eines solchen Programmcodes wesentlich wahrscheinlich, als die direkte zufällige Entstehung des String selbst, der die Millionen Anfangsstelle von Pi repräsentiert.Die skizzierten Ideen sind zum Teil so weitgreifend, dass es nicht verwundert, dass viel davon eher der Vorstellung eines Forschungsprogramms entspricht, denn bereits tatsächlich vorliegender Resultate, weswegen die Ausführungen gelegentlich 'hand waving' werden, was aber bei Aufrechterhaltung des allgemein verständlichen Kontextes, kaum anders möglich ist. Ungeachtet dessen, ist Seth Lloyds 'Programming the Universe' eines der faszinierendsten und inspirierendsten Science Bücher der letzten Jahre, der Autor scheut sich nicht, große Fragen aufzugreifen und neue Zusammenhänge plausibel zu machen.Ein Index (Stichwortverzeichnis) hätte sicher zur Übersichtlichkeit des Buches beigetragen – darauf wurde leider verzichtet. Aber in einem Anhang wurden Hinweise und Empfehlungen zur weiterführenden Lektüre zusammen gestellt, die Liste umfasst auch einige arXiv Preprints des Autors, die es dem interessierten Lesers ermöglichen, in die angesprochen Themen tiefer einzudringen.

Un bon ouvrage didactique qui permet de mieux comprendre les mécanismes de la physique quantique appliqués au domaine de l'informatique (informatique quantique).Seth Lloyd est ici un bon pédagogue, qui explique de manière simple les mécanismes qui régissent l'infiniment petit (les atomes et les quarks) et l'infiniment grand (l'univers dans sa globalité).L'auteur dit ainsi que notre Univers est un ordinateur quantique qui génère et brasse des quantités colossales d'informations. La résultante étant la création de ce que nous percevons, voyons et sommes.Bref, un petit livre très éclairant pour les néophytes (avec quelques connaissances), les curieux, mais aussi les informaticiens et les physiciens.