This chapter asks a bold but careful question: Could information be as fundamental as the forces we already know? Not a new push or pull like gravity, but a deeper organising substrate that shapes what forces can do. We trace the idea from quantum mechanics—where gaining “which-path” information destroys interference and erasing it restores fringes—to Landauer’s principle that information has thermodynamic cost. Wheeler’s “it from bit” frames reality as answers to yes/no questions, while Bell tests and no-signalling show that entanglement changes what correlations are possible without sending messages. In gravity, black-hole thermodynamics links information to area: the Bekenstein–Hawking law and holography suggest that a region’s information capacity scales with its boundary, inspiring Susskind’s complementarity and modern takes on the information paradox. We then read the universal constants https://www.w3.org/1998/Math/MathML" display="inline"> c , G , h , k B , α as limits on how fast, how finely, and how reliably information can move, resolve, and persist—constraints that also underwrite life’s local order against entropy. The claim is not that “information” is a fifth force in the Newtonian sense, but that it acts as a universal constraint/ledger steering admissible dynamics across quantum theory, thermodynamics, and spacetime. Seen this way, unification may be an information principle in disguise.
This chapter asks a bold but careful question: Could information be as fundamental as the forces we already know? Not a new push or pull like gravity, but a deeper organising substrate that shapes what forces can do. We trace the idea from quantum mechanics—where gaining “which-path” information destroys interference and erasing it restores fringes—to Landauer’s principle that information has thermodynamic cost. Wheeler’s “it from bit” frames reality as answers to yes/no questions, while Bell tests and no-signalling show that entanglement changes what correlations are possible without sending messages. In gravity, black-hole thermodynamics links information to area: the Bekenstein–Hawking law and holography suggest that a region’s information capacity scales with its boundary, inspiring Susskind’s complementarity and modern takes on the information paradox. We then read the universal constants https://www.w3.org/1998/Math/MathML" display="inline"> c , G , h , k B , α as limits on how fast, how finely, and how reliably information can move, resolve, and persist—constraints that also underwrite life’s local order against entropy. The claim is not that “information” is a fifth force in the Newtonian sense, but that it acts as a universal constraint/ledger steering admissible dynamics across quantum theory, thermodynamics, and spacetime. Seen this way, unification may be an information principle in disguise.
Black holes are windows into the deepest structures of reality, where quantum mechanics, thermodynamics, and geometry converge. In this pedagogical preprint we explore how quantum entanglement entropy provides a microscopic foundation for black hole thermodynamics. Starting from rst principles of quantum information theory, we introduce entanglement entropy, the area law, and Hawking radiation, then proceed to modern results: the Ryu-Takayanagi formula, quantum extremal surfaces, the Page curve, replica wormholes, and the island formula. Throughout, the emphasis is on physical intuition. No prior knowledge of string theory or loop quantum gravity is assumed.
For a physicist, all the world is information. The Universe and its workings are the ebb and flow of information. We are all transient patterns of information, passing on the recipe for our basic forms to future generations using a four-letter digital code called DNA. In this engaging and mind-stretching account, Vlatko Vedral considers some of the deepest questions about the Universe and considers the implications of interpreting it in terms of information. He explains the nature of information, the idea of entropy, and the roots of this thinking in thermodynamics. He describes the bizarre effects of quantum behaviour -- effects such as 'entanglement', which Einstein called 'spooky action at a distance', and explores cutting edge work on harnessing quantum effects in hyperfast quantum computers, and how recent evidence suggests that the weirdness of the quantum world, once thought limited to the tiniest scales, may reach into the macro world. Vedral finishes by considering the answer to the ultimate question: where did all of the information in the Universe come from? The answers he considers are exhilarating, drawing upon the work of distinguished physicist John Wheeler. The ideas challenge our concept of the nature of particles, of time, of determinism, and of reality itself. This edition includes a new foreword from the author, reflecting on changes in the world of quantum information since first publication. Oxford Landmark Science books are 'must-read' classics of modern science writing which have crystallized big ideas, and shaped the way we think.
The slogan ``information is physical,'' introduced by Rolf Landauer and developed through quantum information theory and black-hole thermodynamics, has achieved near-axiomatic status in modern physics. Yet the ontological status of information remains surprisingly underexamined: most discussions either reduce information to a form of energy or treat it as a purely mathematical object. This paper proposes a third position. I argue that information is neither a physical substance nor a free-floating abstraction, but rather \emph{the structure of physically realizable alternatives} -- a counterfactual structure that a physical system instantiates in virtue of the possibility space available to it. Building on Shannon's combinatorial definition, the Landauer principle, the no-cloning theorem, and the black-hole information paradox, I show that the informational content of any physical event is constituted by the set of outcomes that \emph{could have occurred} but did not. This counterfactual reading dissolves several persistent confusions: it explains why erasing information dissipates heat without making information ``material,'' why quantum superposition is informationally richer than any classical mixture, and why information loss in black holes is physically significant beyond mere bookkeeping. The proposal sits within a structural-realist framework but departs from standard structural realism by locating the relevant structure in modal, not merely actual, relations. I conclude by sketching implications for the foundations of quantum mechanics, quantum gravity, and scientific ontology more broadly.
This preprint examines the thermodynamic limits of information registration and their implications for quantum mechanics, black hole physics, and cosmology. Building on Landauer’s principle, it argues that registration and erasure are physically inseparable operations, each incurring the same energetic toll of kBTln2 per bit. From this perspective, quantum “collapse” is reframed as collapse insolvency, the condition that stable records cannot be formed beyond an energy constrained ceiling. The paper develops a Six Tier Insolvency Model, distinguishing between global constraints (Bekenstein–Hawking entropy, Landauer throughput, empirical ceilings) and local bottlenecks (Hawking flux, flux dilution, observer collapse limit). It derives striking insolvency ratios (~10⁻⁵⁶ globally and ~10⁻⁴⁷ locally), quantifying the gap between the entropy accessible in principle and that which any finite observer can render. The analysis introduces the Goldilocks Rendering Zone (GRZ), a universal band where collapse can occur: too little flux leaves no record, too much flux exceeds solvency. This provides a unified account that links quantum measurement, biological information processing, and black hole horizons under the same energetic constraint. The framework is falsifiable. It predicts a hard ceiling of ~10¹² bits·s⁻¹·m⁻² for sustained registration under standard conditions (300 K, 1 W/m²). A single reproducible counterexample would suffice to overturn the model.
What is information? A short answer could be: Anything that changes our minds and states of thinking! Information is virtual. It can be carried by speech, an image, scratches on a stone, patterns in a photon field, the connections of neurons in our brains or even by the wavefunction of an electron. Information does not depend on the actual means of transmission nor does its identity change when changing the carrier. Information is physical. It needs to be sustained by a physical substrate and rearranging that substrate to contain the wanted information requires to spend energy or work. Without a physical world, information can not be stored, processed, or transmitted. Our world is permeated with different representations of information. Actually Information about the physical laws governing our Universe can be found everywhere and in everything. Could it then be that the real fundamental elements of this world are tiny bits of information? Could we get it from bit?1 A number of researcher investigate this possibility, and several of their attempts to recover physical laws from the principles governing information are reported about in this special issue on physics of information. The articles by Gregg Jaeger,2 by Ariel Caticha,3 and by John Skilling and Kevin Knuth4 address the reconstruction of quantum mechanics from information theory. Furthermore, Kevin Knuth and James Walsh5 show how to recover space-time from particles sending each others signals in an initially geometry-free setting. A central element of most works on information is the concept of a probability. Probabilities can be defined via various routes. Most familiar might be their definitions by the frequentists school as relative frequencies of events (in the limit of infinite amounts of such). A more general definition of probabilities is the Bayesians' one, which regards probabilities as quantifiers of statements, expressing how much those should be expected to be true. Although this definition looks subjective on the first glance, it rests on a solid mathematical theorem by Richard Cox6 that any extension of binary logic to a continuum of single valued truthfulness quantifier that respects a minimum of requirements must be isomorphic to probability theory. And this definition turns out to embrace the frequentists' definition in case that infinite numbers of comparable events are actually available and can be counted. The majority of authors of this special issues seem to favor the Bayesian perspective, which is probably a result of our own, the guest editors', preference and not necessarily a reflection of the prevailing position of contemporary scientists. The different views on probabilities of frequentists and Bayesians are addressed by the article of Allen Caldwell.7 He builds a bridge between these antagonistic camps by explaining frequentists' constructions in a Bayesian language. In particular, his argumentation why the omnipresent p-value in statistical and experimental literature might often capture a relevant signal of model misfit is reassuring, given that a large fraction of our medical system is based on decisions backed up by p-values. A Bayesian might add that it would be even more reassuring, if a system rigorously build on logic and its continuous extension would be used for decisions affecting live-or-death questions. The laws governing probabilities themselves seem to reflect that of more elementary mathematical structures. Kevin Knuth shows how these emerge from lattice theory, which deals with relations in partially ordered sets like that of collections of possibilities.8 The sum rule of probability theory is a direct consequence of the underlying lattice structure. Interestingly, a number of other theories are resting also on such lattices and therefore exhibit their own versions of sum rules: measures of sets, mutual information, the Euler characteristics of topological spaces, as well as quantum mechanical interactions that are quantified by pairs of numbers, the real and imaginary parts of complex probability amplitudes (see also4). The theory of information has very practical application in physics and elsewhere. Manfred Opper discusses how the solutions of stochastic differential equations can be inferred via variational methods, which have their origin in thermodynamics.9 Torsten Enßlin introduces information field theory (IFT), the information theory for fields, as a means to infer the configuration of a physical field from incomplete and noisy data.10 The mathematical apparatus for this is that of quantum field theory (QFT), just with ordinary probabilities instead of complex probability amplitudes as in the latter. Could it be that the difference between IFT and QFT is just be the same as between classical information theory and quantum mechanics, the transition from real valued to complex valued quantifier for statements? Anyhow, any practical inference machinery, be it for dynamical systems or for fields, requires sophisticated numerical methods. Michael Betancourt reviews Markov Chain Monte Carlo Methods to calculate expectation values over high dimensional probabilities.11 Theo Steininger and coworkers present the NIFTy3 software package for numerical information field theory calculations, which can handle very high dimensional field inference problems.12 Finally, in an article focused on the subtleties of the Monty Hall problem and mostly aiming at information theoretical entertainment, Torsten Enßlin and Margret Westercamp investigate the possibility that human intuition might be more rational than contemporary psychology thinks.13 A number of possible topics for an issue on physics of information are not addressed here. We would have loved to have articles on Landauer's principle, which states that erasing information has to cost energy, on QBism, a Bayesian version of quantum mechanics, on artificial and biological neural networks, as well as any other aspect of the information-soaked biological world. What has a reader of this special issue to be equipped with in order to follow the lines of thoughts? In addition to the usual physicist's education, the minimal additional equipment are the basics of probability theory and the concept of entropy. Most of the other concepts used in the articles rest on those and are introduced there. Let A, B, and C be propositions (or possibilities). The probability P ( A | B ) of A being true assuming that B is true is a number between 0 and 1, with P ( A | B ) = 1 expressing certainty of A under B ( B ⇒ A ) and P ( A | B ) = 0 expressing certainty of not A being the case under B ( B ⇒ ¬ A ).
Newtonian gravity, at first sight, does not imply new examples for quantum mechanics because of its close similarity with static electric forces. A massive object moving in an approximately constant gravitational field near the surface of Earth is subject to a linear potential https://www.w3.org/1998/Math/MathML" display="inline"> V ( z ) = m g z , while a 2-mass system is subject to Newton's potential https://www.w3.org/1998/Math/MathML" display="inline"> V ( r ) = − G m 1 m 2 / r and therefore resembles the hydrogen model. Moreover, gravitational effects in lab systems are usually weak and would require sensitive measurements to be noticed.