Introduction Of John Wheeler's “Really Big Questions,” the one on which the most progress has been made is “It from bit?” – does information play a significant role at the foundations of physics? It is perhaps less ambitious than some of the other questions, such as “How come existence?”, because it does not necessarily require a metaphysical answer. And unlike, say, “Why the quantum?”, it does not require the discovery of new laws of nature: there was room for hope that it might be answered through a better understanding of the laws as we currently know them, particularly those of quantum physics. And this is what has happened: the better understanding is the quantum theory of information and computation. How might our conception of the quantum physical world have been different if “It from bit” had been a motivation from the outset? No one knows how to derive it (the nature of the physical world) from bit (the idea that information plays a significant role at the foundations of physics), and I shall argue that this will never be possible. But we can do the next best thing: we can start from the qubit. Qubits To a classical information theorist, a bit is an abstraction: a certain amount of information. To a programmer, a bit is a Boolean variable. To an engineer, a bit is a “flip-flop” – a piece of hardware that is stable in either of two physical states.
Introduction Of John Wheeler's “Really Big Questions,” the one on which the most progress has been made is “It from bit?” – does information play a significant role at the foundations of physics? It is perhaps less ambitious than some of the other questions, such as “How come existence?”, because it does not necessarily require a metaphysical answer. And unlike, say, “Why the quantum?”, it does not require the discovery of new laws of nature: there was room for hope that it might be answered through a better understanding of the laws as we currently know them, particularly those of quantum physics. And this is what has happened: the better understanding is the quantum theory of information and computation. How might our conception of the quantum physical world have been different if “It from bit” had been a motivation from the outset? No one knows how to derive it (the nature of the physical world) from bit (the idea that information plays a significant role at the foundations of physics), and I shall argue that this will never be possible. But we can do the next best thing: we can start from the qubit. Qubits To a classical information theorist, a bit is an abstraction: a certain amount of information. To a programmer, a bit is a Boolean variable. To an engineer, a bit is a “flip-flop” – a piece of hardware that is stable in either of two physical states.
Whoever it was who first contracted the words 'binary digit' to form 'bit' can hardly have realised that he (she?) was coining a term not only for the smallest unit of information but also for the smallest unit of 'being' – or so the general relativist John Archibald Wheeler would have us believe. 'It from bit' is his declamation of the ultimate fount of significance of every physical quantity: all we can know about photons, fields, black holes – you name 'it' – depends at root, he emphasizes, on yes-or-no indications. Pursuing the implications of this observation through quantised strings, quantum measurement theory, computational representations of physical laws, information theory, thermodynamic entropy, evolution... those, he says, are routes to that happy state of perceived simplicity and beauty when we finally know the Final Answer to the question: 'How come existence?'
We know how to use the “rules” of quantum physics to build lasers, microchips, and nuclear power plants, but when students question the rules themselves, the best answer we can give is often, “The world just happens to be that way.” Yet why are individual outcomes in quantum measurements random? What is the origin of the Schrodinger equation? In a paper [1] appearing in Physical Review A, Giulio Chiribella at the Perimeter Institute in Waterloo, Canada, and Giacomo Mauro D’Ariano and Paolo Perinotti at the University of Pavia, Italy, offer a framework in which to answer these penetrating questions. They show that by making six fundamental assumptions about how information is processed, they can derive quantum theory. (Strictly speaking, their derivation only applies to systems that can be constructed from a finite number of quantum states, such as spin.) In this sense, Chiribella et al.’s work is in the spirit of John Wheeler’s belief that one obtains “it from bit,” in other words, that our account of the universe is constructed from bits of information, and the rules on how that information can be obtained determine the “meaning” of what we call particles and fields.
The main mystery of quantum mechanics is contained in Wheeler's delayed choice experiment, which shows that the past is determined by our choice of what quantum property to observe. This gives the observer a participatory role in deciding the past history of the universe. Wheeler extended this participatory role to the emergence of the physical laws ("law without law"). Since what we know about the universe comes in yes/no answers to our interrogations, this led him to the idea of "it from bit" (which includes the participatory role of the observer as a key component). The yes/no answers to our observations ("bit") should always be compatible with the existence of at least a possible reality - a global solution ("it") of the Schrodinger equation. I argue that there is in fact an interplay between "it" and "bit". The requirement of global consistency leads to apparently acausal and nonlocal behavior, explaining the weirdness of quantum phenomena. As an interpretation of Wheeler's "it from bit" and "law without law", I discuss the possibility that the universe is mathematical, and that there is a "mother of all possible worlds" - named the "Axiom Zero".
“I refute it thus!” Samuel Johnson famously dismissed Bishop George Berkeley's argument for the unreality of matter by kicking a large stone (Boswell, 1823). In the light of modern physics, however, Johnson's simple reasoning evaporates. Apparently solid matter is revealed, on closer inspection, to be almost all empty space, and the particles of which matter is composed are themselves ghostly patterns of quantum energy, mere excitations of invisible quantum fields, or possibly vibrating loops of string living in a ten-dimensional space–time (Greene, 1999). The history of physics is one of successive abstractions from daily experience and common sense, into a counterintuitive realm of mathematical forms and relationships, with a link to the stark sense data of human observation that is long and often tortuous. Yet at the end of the day, science is empirical, and our finest theories must be grounded, somehow, “in reality.” But where is reality? Is it in acts of observation of the world made by human and possibly non-human observers? In records stored in computer or laboratory notebooks? In some objective world “out there”? Or in a more abstract location? The ground of reality When a physicist performs an experiment, he or she interrogates nature and receives a response that, ultimately, is in the form of discrete bits of information (think of “yes” or “no” binary answers to specific questions), the discreteness implied by the underlying quantum nature of the universe (Zeilinger, 2004). Does reality then lie in the string of bits that come back from the set of all observations and experiments – a dry sequence of ones and zeros? Do these observations merely transfer really-existing bits of information from an external world reality to the minds of observers, or are the bits of information created by the very act of observation/experiment? And – the question to which this entire discussion is directed – are bits of “classical” information the only sort of information that count in the reality game, or does an altogether different form of information underpin reality? In short, where is the ontological ground on which our impression of a really-existing universe rests?
Introduction First a word of thanks. When I first came across the papers of John Archibald Wheeler on the foundations of quantum mechanics, most of them reprinted in Wheeler and Zurek (1983), I could not believe what I read. Finally here was a colleague of worldwide reputation, given his many contributions to theoretical physics, who was not afraid to discuss openly the conceptual problems of quantum mechanics. The outstanding feature of Professor Wheeler's viewpoint is his realization that the implications of quantum mechanics are so far-reaching that they require a completely novel approach in our view of reality and in the way we see our role in the universe. This distinguishes him from many others who in one way or another tried to save pre-quantum viewpoints, particularly the obviously wrong notion of a reality independent of us. Particularly remarkable is Professor Wheeler's austerity in thinking. He tries to use as few concepts as possible and to build on this the whole of physics. A fascinating case in point is the title of one of his papers “Law without law,” the attempt to arrive at the laws of nature without assuming any law a priori. For me personally his work on fundamental issues in quantum mechanics has been particularly inspiring. The questions he raises are exceptionally far-reaching and some of his concepts in the foundations of physics are so radical that calling them revolutionary would not do them justice.
In his 1989 essay, John Archibald Wheeler has tried to answer the eternal question of existence. He did it by searching for links between information, physics, and quanta. The main concept emerging from his essay is that "every physical quantity, every it, derives its ultimate significance from bits, binary yes-or-no indications". This concept has been summarized in the catchphrase "it from bit". In the Wheeler's essay, it is possible to read several times the echoes of the philosophy of Niels Bohr. The Danish physicist has pointed out how the quantum and relativistic physics - forcing us to abandon the anchor of the visual reference of common sense - have imposed a greater attention to the language. Bohr did not deny the physical reality, but recognizes that there is always need of a language no matter what a person wants to do. To put it as Carlo Sini, language is the first toolbox that man has at hands to analyze the experience. It is not a thought translated into words, because to think is to operate with signs as reminded us by various philosophers from Leonardo da Vinci to Ludwig Wittgenstein. [...]