‘Sprache und Wirklichkeit in der modernen Physik’ is the title of a lecture Heisenberg gave in 1960 at the Bayerische Akademie der Schönen Künste. The polemics that had accompanied the establishment of quantum mechanics were over by then and the so-called problems of its foundations had lost much of their initial interest. Einstein had been dead for some years. Right up to the end he had expressed his profound dissatisfaction with a theory which, in his opinion, had something unreasonable about it. With the volume dedicated to him by the community of physicists and philosophers, the long debate between Bohr and Einstein had come to an end. It had been a disappointing conclusion, marked by the reaffirmation of the respective viewpoints of two scientists who by now found great difficulty even in defining a common code of communication. As though seeking to narrow the gap between them, Heisenberg took the opportunity to underline the existence of a common feature in their contributions to 20th century physics. Their discoveries had in fact made it possible to recognize that ‘even the fundamental and most elementary concepts of science, such as space, time, place, velocity, have become problematic and must be re-examined’. The conceptual and cognitive implications of relativity and of quantum mechanics were obviously different but Heisenberg maintained that both theories asked the same question: ‘Does the language we use when we speak of experiments correspond to the artificial language of mathematics which, as we know, describes real relationships correctly; or has it become separated from it so that we must be content with imprecise linguistic formulations and only return to the artificial language of mathematics when we are forced to express ourselves with precision?’.
The difficulties of the old quantum theory were largely dispelled by the development of quantum mechanics in the 1920s. First Heisenberg (1925) developed the rather abstract matrix mechanics and soon after Schro¨dinger (1926; see also Eckart, 1926) developed the physically more appealing wave mechanics. Subsequently he showed them to be mathematically equivalent. The physicists were greatly relieved; now they had once again a mathematical formalism that enabled the results of experiments to be calculated. It was possible to move forward. It is certainly a very elegant and indeed beautiful formalism, and does enable the results of many physical measurements to be calculated with great accuracy. It is used daily by atomic and nuclear physicists; there is no other way to make calculations. From the earliest days there has been intense debate about the interpretation of quantum mechanics, and it shows no signs of being settled; if anything it is becoming more intense over the years. As Penrose has remarked, no one understands quantum mechanics. Feynman (1967; see also Sykes, 1994) also admitted that ‘nobody understands quantum mechanics’, and Einstein once remarked: ‘I have thought a hundred times as much about the quantum problems as I have about general relativity theory’ (Pais, 1994, p. 57). It should therefore be evident that the most that can be done here is to try to show where the real difficulties lie, and how the failure to recognize that quantum mechanics is an essentially statistical theory has led to a series of confusing quantum paradoxes. It is just these paradoxes that have often been used to support theological speculations. It is useful to ask what ‘understanding quantum mechanics’ actually means. Certainly it means being able to calculate the results of many measurements. The same applies to Newton’s theory of gravitation, which we understand in the sense that we can use it as a basis of calculation, although we do not really understand the gravitational force itself. Very often, especially in modern physics, the mathematical formalism does not give us the sort of intuitive physical feeling for what is going on that we often obtain from classical mechanics. Perhaps we can never achieve more than this for quantum mechanics. In classical mechanics we can assume that a property that is measured objectively exists prior to the interaction of the measuring apparatus with the observed system. Quantum mechanics, however, ‘is incompatible with the proposition that measurement discovers some unknown but pre-existing property’ (Peres, 1997, p. 14). There is an important distinction between mysteries and absurdities. We may be forced to live with mysteries, but there is no reason why we should put up with absurdities such as the wave-particle duality, tunnelling through potential barriers, acausal events and the collapse of the wave function. These are the quantum paradoxes that will be discussed later on. They arise within the Copenhagen interpretation of quantum mechanics and are solved by other interpretations. These alternative interpretations enable us to make conjectures about what is going on, even though we cannot understand it in detail. This is acceptable and a stimulus to further research. It is certainly difficult enough to understand quantum mechanics, but there is no need to try to visualize logical absurdities in the effort to do so. Quantum mechanics is a mathematical formalism that makes it possible to calculate the results of some experiments. Anything more than this, such as questions about the interpretation of what is measured and whether it tells us what is actually going on in the system being studied, belongs to philosophy. Thus we are concerned here with what is essentially a philosophical debate; if it were just a matter of physics the debate would have been settled long ago. One of the difficulties is that it invokes the results of experiments and uses the language of quantum mechanics. Inevitably this language uses philosophical terms and then it is easy to give the impression that the philosophical propositions are in some way entailed by the physical results. These in turn can influence theological thinking. In order to be quite clear which arguments are justified and which are not, it is essential to separate the three levels of discourse: physical, philosophical and theological. Our task is to relate these together, and this immediately raises the traditional problems of the philosophy of science, including the relation of experiment to theory, and of theory to explanation. We begin by discussing experiments, distinguishing between those that are real and those that are imaginary.
The road on the foundations of science in general consists in (a) making precise what the assumptions are one makes resulting from our measurements (b) holding a “good” balance between theoretical assumptions and genericity of predictions (c) saying as precisely as possible what you mean. Unfortunately, recent work where these three criteria are met is scarce and I often encounter situations where physicists talk about different things in the same words or the other way around, identify distinct concepts (even without being aware of it), or introduce unnecessary hypothesis based upon a too stringent mathematical interpretation of some observation. In this work, I will be as critical as possible and give away those objections against modern theories of physics which have become clear in my mind and therefore transcend mere intuition. All these objections result from the use of unclear language or too stringent assumptions on the nature of reality. Next, we weaken the assumptions and discuss what I call process physics; it will turn out that Bell’s concerns do find a natural solution within this framework.
Quantum mechanics is usually defined in terms of some loosely connected axioms and rules. Such a foundation is far from the beauty of, e.g., the `principles' underlying classical mechanics. Motivated, in addition, by notorious interpretation problems, there have been numerous attempts to modify or `complete' quantum mechanics. A first attempt was based on so-called hidden variables; its proponents essentially tried to expel the non-classical nature of quantum mechanics. More recent proposals intend to complete quantum mechanics not within mechanics proper but on a `higher (synthetic) level'; by means of a combination with gravitation theory (R Penrose), with quantum information theory (C M Caves, C A Fuchs) or with psychology and brain science (H P Stapp). I think it is fair to say that in each case the combination is with a subject that, per se , suffers from a very limited understanding that is even more severe than that of quantum mechanics. This was acceptable, though, if it could convincingly be argued that scientific progress desperately needs to join forces. Quantum mechanics of a closed system was a beautiful and well understood theory with its respective state being presented as a point on a deterministic trajectory in Liouville space---not unlike the motion of a classical N -particle system in its 6N -dimensional phase-space. Unfortunately, we need an inside and an outside view, we need an external reference frame, we need an observer. This unavoidable partition is the origin of most of the troubles we have with quantum mechanics. A pragmatic solution is introduced in the form of so-called measurement postulates: one of the various incompatible properties of the system under consideration is supposed to be realized (i.e. to become a fact, to be defined without fundamental dispersion) based on `instantaneous' projections within some externally selected measurement basis. As a result, the theory becomes essentially statistical rather than deterministic; furthermore there is an asymmetry between the observed and the observing. This is the point where consciousness may come in. Complemented by an introduction and several appendices, Henry Stapp's book consists essentially of three parts: theory, implications, and new developments. The theory part gives a very readable account of the Copenhagen interpretation, some aspects of a psychophysical theory, and, eventually, hints towards a quantum foundation of the brain--mind connection. The next part, `implications', summarizes some previous attempts to bridge the gap between the working rules of quantum mechanics and their possible consequences for our understanding of this world (Pauli, Everett, Bohm, Heisenberg). The last section, `new developments', dwells on some ideas about the conscious brain and its possible foundation on quantum mechanics. The book is an interesting and, in part, fascinating contribution to a field that continues to be a companion to `practical' quantum mechanics since its very beginning. It is doubtful whether such types of `quantum ontologies' will ever become (empirically) testable; right now one can hardly expect more than to be offered some consistent `grand picture', which the reader may find more or less acceptable or even rewarding. Many practicing quantum physicists, though, will remain unimpressed. The shift from synthetic ontology to analytic ontology is the foundation of the present work. This means that fundamental wholes are being partitioned into their ontologically subordinate components by means of `events'. The actual event, in turn, is an abrupt change in the Heisenberg state describing the quantum universe. The new state then defines the tendencies associated with the next actual event. To avoid infinite regression in terms of going from one state of tendencies to the next, consciousness is there to give these events a special `feel', to provide a status of `intrinsic actuality'. The brain of an alert human observer is similar in an important way to a quantum detection device: it can amplify small signals to large macroscopic effects. On the other hand, actual events are not postulated to occur exclusively in brains. They are more generally associated with the formation of records. Records are necessarily part of the total state of the universe: it is obvious that the state of the universe cannot undergo a Schrödinger dynamics and at the same time record its own history. `The full universe consists therefore of an exceedingly thin veneer of relatively sluggish, directly observable properties resting on a vast ocean or rapidly fluctuating unobservable ones.' The present ideas also bear on how the world should be seen to develop. While conventional cosmology encounters problems as to how to define the intial conditions, which would enter the governing equations of motion, here `the boundary conditions are set not at some initial time, but gradually by a sequence of acts that imposes a sequence of constraints. After any sequence of acts there remains a collection of possible worlds, some of which will be eliminated by the next act.' Connected with those acts is `meaning': there has always been some speculation about the special significance of local properties in our understanding of the world. One could argue that correlations (even the quantum correlations found, e.g., in the EPR-experiments) were as real as anything else. But also Stapp stresses the special role of locality: the `local observable properties, or properties similar to them are the natural, and perhaps exclusive, carriers of meaning in the quantum universe. From this point of view the quantum universe tends to create meaning.' This sounds like an absolute concept: meaning not with respect to something else, but defined intrinsically---not easy to digest. The role of consciousness in the developing quantum universe requires more attention. `The causal irrelevance of our thoughts within classical physics constitutes a serious deficiency of that theory, construed as a description of reality.' This is taken to be entirely different within quantum mechanics. `The core idea of quantum mechanics is to describe our activities as knowledge-seeking and knowledge-using agents.' `21st century science does not reduce human beings to mechanical automata. Rather it elevates human beings to agents whose free choices can, according to the known laws, actually influence their behaviour.' An example with respect to perception is discussed: `Why, when we look at a triangle, do we experience three lines joined at three points and not some pattern of neuron firings?' The brain `does not convert an actual whole triangle into some jumbled set of particle motions; rather it converts a concatenation of separate external events into the actualization of some single integrated pattern of neural activity that is congruent to the perceived whole triangle.' How convincing is this proposal? It is hard to tell. I think Henry Stapp did a good job, but there are tight limitations to any such endeavour. Quantum mechanics is often strange indeed, but it also gives rise to our classical world around us. For the emergence of classicality jumps and measurement projections (the basic phenomena connected with those fundamental events of choice) are not needed. Therefore, I doubt whether the explanation of the evolution of our world really allows (or requires) that much free choice. On the other hand, most scientist will agree that empirical science was not possible without free will: we could not ask independent questions if this asking was part of a deterministic trajectory. The fact that the result of a quantum measurement is indeterminate (within given probabilities) does certainly not explain free will. How about the type of measurment? The experimentalist will have to assume that he can select the pertinent observable within some limits. But given a certain design the so-called pointer basis (producing stable measurement results) is no longer a matter of free choice. `The main theme of classical physics is that we live in a clocklike universe.' Today it is often assumed that the universe was a big (quantum-) computer or a cellular automaton. Many would be all too happy to leave that rather restrictive picture behind. But where to go? Stapp suggests giving consciousness a prominent role: `The most profound alteration of the fundamental principles was to bring consciousness of human beings into the basic structure of the physical theory.' How far we are able to go in this direction will depend on the amount of concrete research results becoming available to support this view.
Foundations of physics · For the general reader The Relational Architecture of Time Emergent temporal order, delayed-choice photon experiments, and the thermodynamic arrow — a complete mathematical account, explained from the ground up János Gábor Melegh The Relational Architecture of TimeEmergent temporal order, delayed-choice photon experiments, and the thermodynamic arrow. Copyright © 2026 János Gábor Melegh. All rights reserved. No part of this book may be reproduced in any form without written permission from the author, except for brief quotations in reviews and scholarly works. This book unifies and expands two research manuscripts by the author: Time as an Emergent Relational Structure (2026) and Relational Time Structure in Delayed-Choice Photon Experiments (axiomatically extended version, 2026). Every definition, theorem, proof, and derivation of those works is reproduced here in full and without abridgement; the surrounding prose has been substantially expanded so that a motivated reader without formal training in physics or mathematics can follow the entire argument. First English edition, 2026. Preface How to Read This Book This is a book about a deceptively simple question: what is time, physically? Not what a clock reads, and not how time feels, but what structure in the physical world earns the name "time" at all. The answer defended here can be stated in one sentence: time is not a fundamental ingredient of the universe but an emergent, relational structure — an ordering that arises when physical descriptions defined through interaction fit together consistently, with its familiar one-way direction supplied separately by thermodynamics. That single sentence carries a lot of machinery, and this book unpacks all of it. The book makes an unusual promise, and it is worth stating explicitly: The promise of this book Nothing has been simplified away. Every equation, every definition, every theorem, and every proof from the underlying research papers appears here in full. What has been added — greatly — is explanation: before and after each formal step you will find plain-language accounts of what the symbols say, why the step matters, and what would go wrong without it. If you skip the equations entirely, the prose still tells a complete story. If you read the equations, the prose tells you exactly how to read them. Throughout the book you will meet a small family of recurring boxes, each with a fixed job: In plain language (copper boxes) — the intuition. What a formal statement means in everyday terms, often with an analogy. Definitions (blue boxes) — precise introductions of new mathematical objects. These are the vocabulary of the theory. Theorems (framed boxes) — the claims that are actually proved, followed by their proofs in full. A proof ends with the traditional square symbol □. Warnings and scope limits (red boxes) — the places where the theory deliberately stops claiming things. These boxes are part of the scientific content, not decoration: a theory earns trust partly by declaring its own boundaries. A five-minute notation primer Readers who have never used the notation of quantum mechanics need only a handful of symbols, all introduced properly when they first appear. As a preview:
∣ψ⟩ — a "ket," the standard label for a quantum state. Think of it as the complete catalogue of what quantum theory says about a system.
ρ — a density operator, the more general bookkeeping device for quantum states, including states known only statistically.
Tr — the trace, a summing-up operation.
TrB ("partial trace over
B") means: average away everything about subsystem
B and keep the rest.
P(x∣b) — the probability of outcome
x given setting
b. Ordinary conditional probability.
e1≺e2 — event
e1 causally precedes event
e2; it can influence it.
∑ — a sum;
sup and
inf — the least upper bound and greatest lower bound of a set of numbers, close cousins of "maximum" and "minimum." Everything else — beam splitters, POVMs, quantum channels, entropy, modular flow — is built up step by step in the chapters where it is needed, and Appendix A collects every symbol in one table. The shape of the argument Part I poses the problem of time and develops the conceptual core: relational description, the principle of relational consistency, the removal of subjective experience from the foundations, and the division of labor between relational ordering and thermodynamic direction. Part II takes the framework into the laboratory. It builds the full mathematical toolkit from scratch and then works through the two most notorious "time-bending" experiments of quantum optics — Wheeler's delayed choice and the delayed-choice quantum eraser — with complete derivations, showing that nothing in them requires the future to reach back into the past. Part III formalizes relational consistency exactly, explains what a physical record is, de-mystifies the "observer" (including a careful treatment of the Wigner's-friend and Frauchiger–Renner thought experiments), and shows the correct use of causal event graphs. Part IV separates order from direction, develops the thermodynamic arrow, connects the framework to thermal time and to neighboring research programs. Part V asks the hardest questions of any theory — what does it mean, and how could it be wrong? — and closes with a complete empirical research program and conclusions. What this book does not claim This book does not announce a new physical force, a new dynamical law, or an experimental result that contradicts standard quantum mechanics. Its framework is deliberately, provably empirically equivalent to standard quantum theory in every laboratory situation treated here. Its contribution is a rigorously constrained conceptual and mathematical reconstruction: an account of what time is, and of what delayed-choice experiments do and do not show, that is causally clean, fully formalized, and — crucially — falsifiable in the precise, limited sense worked out in Chapter 22. Readers deserve to know which statements are established mathematics, which are structural proposals, and which are open questions; this book labels all three throughout. Contents Table of Contents Preface: How to Read This Book Part I — The Problem of Time 1. Why Time Is a Problem 2. Relational Descriptions in Contemporary Physics 3. Relational Consistency as a Structural Principle 4. Time Without Experience 5. Relational Ordering and Thermodynamic Asymmetry 6. Ontological Implications and Open Questions Part II — The Laboratory of Time 7. Aim and Scientific Status 8. The Experimental Foundation 9. The Mathematical Toolkit 10. Postulates of the Relational-Time Delayed-Choice Model 11. Wheeler's Delayed Choice: The Complete Two-Path Derivation 12. The Delayed-Choice Quantum Eraser: A Density-Matrix Derivation 13. The General No-Signalling Theorem Part III — Consistency, Records, and the Event Graph 14. Relational Consistency: Exact and Experimental Formalization 15. Physical Records, Decoherence, and the Observer De-Mystified 16. Relational Time and the Correct Use of the Event Graph Part IV — The Arrow and the Landscape 17. Relational Order and the Thermodynamic Direction of Time 18. Distinctions from Related Approaches 19. A Formal Bridge: Consistent Quantum Histories 20. Separating Temporal Consistency from Quantum Coherence Part V — Meaning and Testability 21. What Does "Determined Later" Mean, Mathematically? 22. Empirical Content, Falsifiability, and a Research Program 23. Conclusions Back Matter Appendix A — Notation and Conceptual Correspondence Appendix B — The Logical Core in a Single Chain of Formulas Appendix C — Claim–Assumption Matrix References Part I The Problem of Time In which time is neither denied nor assumed, but asked to explain itself — and the concepts of relational description, relational consistency, and the thermodynamic arrow are assembled. Chapter 1 Why Time Is a Problem The conceptual status of time remains deeply problematic in contemporary physics. Relativity eliminates absolute simultaneity; quantum theory challenges the notion of observer-independent states; and neither framework explains how temporal structure itself arises. Ask a physicist of the nineteenth century what time is, and the answer would have been serene: time is a universal, externally given parameter. Every event in the universe happens at some moment of a single cosmic clock, and physics describes how things change as that clock ticks. Newton wrote it into the foundations: absolute time "flows equably without regard to anything external." This picture is intuitive, it matches everyday experience, and it is built into the very grammar of classical mechanics, where every equation of motion says how a quantity changes with respect to
t — a
t that is simply assumed to be there, the same for everyone, everywhere. Modern physics profoundly destabilized this picture — twice, from two independent directions. The first blow came from special relativity. Einstein's 1905 analysis showed that there is no such thing as absolute simultaneity: whether two distant events happen "at the same time" depends on the observer's state of motion. Time intervals themselves are frame-dependent. This is not a limitation of our measuring devices; it is a structural feature of spacetime. There is no privileged universal "now" slicing the universe into past and future — no preferred foliation, in the technical vocabulary — that all observers could agree on. What relativity leaves behind is a network of relations: which events can influence which, encoded in the invariant light-cone structure. The second blow came from quantum theory, which undermines something even more basic: the idea that a physical system simply has a defin
Since this book is closely connected to quantum mechanics, these introductory words will briefly and informally recall some postulates of this theory. Interested readers are urged to consult traditional books on quantum mechanics to complement the discussion ahead and for descriptions of experimental evidence that give rise to the postulates. In physics there are several “equivalent formulations” of quantum mechanics, and a catalogue of the most important appears in [StyO2]. The discussion here is restricted to the nonrelativistic case.