The seminal work by one of the most important thinkers of the twentieth century, Physics and Philosophy is Werner Heisenberg's concise and accessible narrative of the revolution in modern physics, in which he played a towering role. The outgrowth of a celebrated lecture series, this book remains as relevant, provocative, and fascinating as when it was first published in 1958. A brilliant scientist whose ideas altered our perception of the universe, Heisenberg is considered the father of quantum (...) physics; he is most famous for the Uncertainty Principle, which states that quantum particles do not occupy a fixed, measurable position. His contributions remain a cornerstone of contemporary physics theory and application. (shrink)

The seminal work by one of the most important thinkers of the twentieth century, Physics and Philosophy is Werner Heisenberg's concise and accessible narrative of the revolution in modern physics, in which he played a towering role. The outgrowth of a celebrated lecture series, this book remains as relevant, provocative, and fascinating as when it was first published in 1958. A brilliant scientist whose ideas altered our perception of the universe, Heisenberg is considered the father of quantum (...) physics; he is most famous for the Uncertainty Principle, which states that quantum particles do not occupy a fixed, measurable position. His contributions remain a cornerstone of contemporary physics theory and application. Book jacket. (shrink)

It is well known that, in classical theory, Liouville's theorem shows that if an ensemble of systems is distributed over a small element of volume in phase space, the ensemble fills a region of equal volume at all later instants of time. In quantum mechanics, the uncertainty principle is associated with the products of the errors in conjugate coordinates and momenta, and such products can be interpreted in terms of volume elements in phase space. Comparison of these two (...) facts leads to the assertion in the interesting volume on “Statistical Mechanics” recently published by J. E. and M. G. Mayer that “The Liouville theorem is essential for the complete understanding of the uncertainty principle. (shrink)

The research has three objectives: 1) to study the concept of Heisenberg’s uncertainty principle, 2) to study the concept of reality and knowledge in Buddhist philosophy, and 3) to analyze the concept of Heisenberg’s uncertainty principle in Buddhist philosophical perspective. This is documentary research. In this research, it was found that Heisenberg's uncertainty principle refers to the experiment of thought while studying physical reality on smaller particles than atoms where at (...) the present no theory of Physics can clearly explain such properties. In this respect, the mentioned principle is utilized to predict the pairs of a certain attribute of physics, position, and momentum, for instance. The accuracy of position, however, cannot be precisely yielded in advance by such a principle. In other words, it is impossible to measure the position and momentum of a quantum particle at the same time. In the study of the ultimate reality on the matter in the Buddhist philosophy, it showed that corporeality in nature is conditioned by cause and effect and thereby falling under the three common characteristics: 1) impermanence, 2) state of suffering, and 3) state of non-substantiality. In the study of Heisenberg’s uncertainty principle in the Buddhist philosophical perspective, this research was found that the processes in acquiring certain knowledge of Heisenberg and Buddhist philosophy are by one another in the sense that such knowledge is methodologically acquired through experience, rationality, and intuition because both see the Reality in the same manners, that is, the physical reality is viewed by Heisenberg as the thing that goes under changing state of wave-particle all the times, and the matter is seen by Buddhist philosophy as the impermanence and change depending upon its factors involved and thereby is not-self. However, in the different aspect, on the one hand, Buddhist philosophy utilizes the knowledge on the matter to develop the morality and ethics by which the cessation of suffering could be respectively made, but on the other hand, Heisenberg somehow applies the certain knowledge on physical objects into quantum technology to accommodate the physical comfortability in living life. Suggestions in the application of knowledge gained from this research into benefit were that while Buddhist philosophy can make use of Heisenberg’s uncertainty principle to provide certain help at the time of explanation of three common characteristics being done through the scientific method, science also can utilize knowledge gained from Buddhist philosophy to expand the framework of scientific knowledge which is aimed at studying only the physical objects to be able to study the mental objects through the integration of three epistemological methods as well. (shrink)

In this paper we critically analyse W. Heisenberg’s arguments against the ontology of point particles following trajectories in quantum theory, presented in his famous 1927 paper and in his Chicago lectures (1929). Along the way, we will clarify the meaning of Heisenberg’s uncertainty relation and help resolve some confusions related to it.

Heisenberg’s uncertainty principle is a milestone of twentieth-century physics. We sketch the history that led to the formulation of the principle, and we recall the objections of Grete Hermann and Niels Bohr. Then we explain that there are in fact two uncertainty principles. One was published by Heisenberg in the Zeitschrift für Physik of March 1927 and subsequently targeted by Bohr and Hermann. The other one was introduced by Earle Kennard in the same journal (...) a couple of months later. While Kennard’s principle remains untarnished, the principle of Heisenberg has recently been criticized in a way that is very different from the objections by Bohr and Hermann: there are reasons to believe that Heisenberg’s formula is not valid. Experimental results seem to support this claim. -/- . (shrink)

This paper considers the relationship between quantum uncertainty and the problem of God. Among the issues considered are the existence and essence ofGod, divine action, human freedom, and personal identity. In recent discussions concerning the relative merits of science and religion, thinkers like Ian Barbourand John Haught have suggested several such credible, albeit tentative, connections between the two on the basis of the epistemological limit imposed upon human knowledge by the Heisenberg Uncertainty Principle.

The uncertainty on measurements, given by the Heisenberg principle, is a quantum concept usually not taken into account in General Relativity. From a cosmological point of view, several authors wonder how such a principle can be reconciled with the Big Bang singularity, but, generally, not whether it may affect the reliability of cosmological measurements. In this letter, we express the Compton mass as a function of the cosmological redshift. The cosmological application of the indetermination principle (...) unveils the differences of the Hubble-Lemaître constant value, $$H_0$$, as measured from the Cepheids estimates and from the Cosmic Microwave Background radiation constraints. In conclusion, the $$H_0$$ tension could be related to the effect of indetermination derived in comparing a kinematic with a dynamic measurement. (shrink)

Patrick Aidan Heelan’s The Observable offers the reader a completely articulated development of his 1965 philosophy of quantum physics, Quantum Mechanics and Objectivity. In this previously unpublished study dating back more than a half a century, Heelan brings his background as both a physicist and a philosopher to his reflections on Werner Heisenberg’s physical philosophy. Including considerably broader connections to the contributions of Niels Bohr, Wolfgang Pauli, and Albert Einstein, this study also reflects Heelan’s experience in Eugene (...) Wigner’s laboratory at Princeton along with his reflections on working with Erwin Schrödinger dating from Heelan’s years at the Institute for Advanced Cosmology in Dublin. A contribution to continental philosophy of science, the phenomenological and hermeneutic resources applied in this book to the physical and ontological paradoxes of quantum physics, especially in connection with laboratory science and measurement, theory and model making, will enrich students of the history of science as well as those interested in different approaches to the historiography of science. University courses in the philosophy of physics will find this book indispensable as a resource and invaluable for courses in the history of science. (shrink)

In The Structure of Science, Ernest Nagel finds fault with Werner Heisenberg’s explication of the uncertainty principle. Nagel’s complaint is that this principle does not follow from the impossibility of measuring with precision both the position and the momentum of a particle, as Heisenberg intimates, rather it is the other way around. Recent developments in theoretical physics have shown that Nagel’s argument is more substantial than he could have envisaged. In particular it has become clear (...) that there are in fact two uncertainty principles; as a result, there are four pairs of quantities to examine, whereas Heisenberg considers only one. These findings throw new light on Nagel’s criticism. They enable us to see that his intuition was surprisingly apposite, but also make clear where his argument misses the mark. (shrink)

Heisenberg's principle of indeterminacy or uncertainty has led most theoretical physicists and philosophers to two important steps: 1) the denunciation of the law of physical causality; 2) the decision of biological and psychological problems in favor of indeterminism.

Heisenberg's uncertainty principle is usually taken to express a limitation of operational possibilities imposed by quantum mechanics. Here we demonstrate that the full content of this principle also includes its positive role as a condition ensuring that mutually exclusive experimental options can be reconciled if an appropriate trade-off is accepted. The uncertainty principle is shown to appear in three manifestations, in the form of uncertainty relations: for the widths of the position and momentum (...) distributions in any quantum state; for the inaccuracies of any joint measurement of these quantities; and for the inaccuracy of a measurement of one of the quantities and the ensuing disturbance in the distribution of the other quantity. Whilst conceptually distinct, these three kinds of uncertainty relations are shown to be closely related formally. Finally, we survey models and experimental implementations of joint measurements of position and momentum and comment briefly on the status of experimental tests of the uncertainty principle. (shrink)

Quantum uncertainty relations have deep-rooted significance in the formalism of quantum mechanics. Heisenberg’s uncertainty relations attracted a renewed interest for its applications in quantum information science. Following the discovery of the Heisenberg uncertainty principle, Robertson derived a general form of Heisenberg’s uncertainty relations for a pair of arbitrary observables represented by Hermitian operators. In the present work, we discover a temporal version of the Heisenberg–Robertson uncertainty relations for the measurement of (...) two observables at two different times, where the dynamical uncertainties crucially depend on the time evolution of the observables. The uncertainties not only depend on the choice of observables but also depend on the times at which the physical observables are measured. The time correlated two-time commutator dictates the trade-off between the dynamical uncertainties. We demonstrate the dynamics of these uncertainty relations for a spin-1/2 quantum system and for a quantum harmonic oscillator. We also present the dynamical uncertainty relation in terms of entropies, where the temporal entropic uncertainties are restricted by a time-dependent complementarity factor. The temporal uncertainty relations explored in this work can be experimentally verified with the present quantum technology. (shrink)

I provide a critical commentary regarding the attitude of the logician and the philosopher towards the physicist and physics. The commentary is intended to showcase how a general change in attitude towards making scientific inquiries can be beneficial for science as a whole. However, such a change can come at the cost of looking beyond the categories of the disciplines of logic, philosophy and physics. It is through self-inquiry that such a change is possible, along with the realization of (...) the essence of the middle that is otherwise excluded by choice. The logician, who generally holds a reverential attitude towards the physicist, can then actively contribute to the betterment of physics by improving the language through which the physicist expresses his experience. The philosopher, who otherwise chooses to follow the advancement of physics and gets stuck in the trap of sophistication of language, can then be of guidance to the physicist on intellectual grounds by having the physicist’s experience himself. In course of this commentary, I provide a glimpse of how a truthful conversion of verbal statements to physico-mathematical expressions unravels the hitherto unrealized connection between Heisenberg uncertainty relation and Cauchy’s definition of derivative that is used in physics. The commentary can be an essential reading if the reader is willing to look beyond the categories of logic, philosophy and physics by being ‘nobody’. (shrink)

We consider the Heisenberg uncertainty principle of position and momentum in 3-dimensional spaces of constant curvature K. The uncertainty of position is defined coordinate independent by the geodesic radius of spherical domains in which the particle is localized after a von Neumann–Lüders projection. By applying mathematical standard results from spectral analysis on manifolds, we obtain the largest lower bound of the momentum deviation in terms of the geodesic radius and K. For hyperbolic spaces, we also obtain (...) a global lower bound \, which is non-zero and independent of the uncertainty in position. Finally, the lower bound for the Schwarzschild radius of a static black hole is derived and given by \, where \ is the Planck length. (shrink)

The Cramér–Rao bound, satisfied by classical Fisher information, a key quantity in information theory, has been shown in different contexts to give rise to the Heisenberg uncertainty principle of quantum mechanics. In this paper, we show that the identification of the mean quantum potential, an important notion in Bohmian mechanics, with the Fisher information, leads, through the Cramér–Rao bound, to an uncertainty principle which is stronger, in general, than both Heisenberg and Robertson–Schrödinger uncertainty (...) relations, allowing to experimentally test the validity of such an identification. (shrink)

The issue of energy and its potential localizability in general relativity has challenged physicists for more than a century. Many non-invariant measures were proposed over the years but an invariant measure was never found. We discovered the invariant localized energy measure by expanding the domain of investigation from space to spacetime. We note from relativity that the finiteness of the velocity of propagation of interactions necessarily induces indefiniteness in measurements. This is because the elements of actual physical systems being measured (...) as well as their detectors are characterized by entire four-velocity fields, which necessarily leads to information from a measured system being processed by the detector in a spread of time. General relativity adds additional indefiniteness because of the variation in proper time between elements. The uncertainty is encapsulated in a generalized uncertainty principle, in parallel with that of Heisenberg, which incorporates the localized contribution of gravity to energy. This naturally leads to a generalized uncertainty principle for momentum as well. These generalized forms and the gravitational contribution to localized energy would be expected to be of particular importance in the regimes of ultra-strong gravitational fields. We contrast our invariant spacetime energy measure with the standard 3-space energy measure which is familiar from special relativity, appreciating why general relativity demands a measure in spacetime as opposed to 3-space. We illustrate the misconceptions by certain authors of our approach. (shrink)

Breaking Bad, hailed by Stephen King, Chuck Klosterman, and many others as the best of all TV dramas, tells the story of a man whose life changes because of the medical death sentence of an advanced cancer diagnosis. The show depicts his metamorphosis from inoffensive chemistry teacher to feared drug lord and remorseless killer. Driven at first by the desire to save his family from destitution, he risks losing his family altogether because of his new life of crime. In defiance (...) of the tradition that viewers demand a TV character who never changes, Breaking Bad is all about the process of change, with each scene carrying forward the morphing of Walter White into the terrible Heisenberg. Can a person be transformed as the result of a few key life choices? Does everyone have the potential to be a ruthless criminal? How will we respond to the knowledge that we will be dead in six months? Is human life subject to laws as remorseless as chemical equations? When does injustice validate brutal retaliation? Why are drug addicts unsuitable for operating the illegal drug business? How can TV viewers remain loyal to a series where the hero becomes the villain? Does Heisenberg's Principle of Uncertainty rule our destinies? In Breaking Bad and Philosophy, a hand-picked squad of professional thinkers investigate the crimes of Walter White, showing how this story relates to the major themes of philosophy and the major life decisions facing all of us. (shrink)

It has often been claimed that without drastic conceptual innovations a genuine explanation of quantum interference effects and quantum randomness is impossible. This book concerns Bohmian mechanics, a simple particle theory that is a counterexample to such claims. The gentle introduction and other contributions collected here show how the phenomena of non-relativistic quantum mechanics, from Heisenberg's uncertainty principle to non-commuting observables, emerge from the Bohmian motion of particles, the natural particle motion associated with Schrödinger's equation. This book (...) will be of value to all students and researchers in physics with an interest in the meaning of quantum theory as well as to philosophers of science. (shrink)

A theoretical physicist and feminist theorist, Karen Barad elaborates her theory of agential realism, a schema that is at once a new epistemology, ontology, and ethics.

Hao Wang was one of the few confidants of the great mathematician and logician Kurt Gödel. _A Logical Journey_ is a continuation of Wang's _Reflections on Gödel_ and also elaborates on discussions contained in _From Mathematics to Philosophy_. A decade in preparation, it contains important and unfamiliar insights into Gödel's views on a wide range of issues, from Platonism and the nature of logic, to minds and machines, the existence of God, and positivism and phenomenology. The impact of Gödel's theorem (...) on twentieth-century thought is on par with that of Einstein's theory of relativity, Heisenberg's uncertainty principle, or Keynesian economics. These previously unpublished intimate and informal conversations, however, bring to light and amplify Gödel's other major contributions to logic and philosophy. They reveal that there is much more in Gödel's philosophy of mathematics than is commonly believed, and more in his philosophy than his philosophy of mathematics. Wang writes that "it is even possible that his quite informal and loosely structured conversations with me, which I am freely using in this book, will turn out to be the fullest existing expression of the diverse components of his inadequately articulated general philosophy." The first two chapters are devoted to Gödel's life and mental development. In the chapters that follow, Wang illustrates the quest for overarching solutions and grand unifications of knowledge and action in Gödel's written speculations on God and an afterlife. He gives the background and a chronological summary of the conversations, considers Gödel's comments on philosophies and philosophers, and his attempt to demonstrate the superiority of the mind's power over brains and machines. Three chapters are tied together by what Wang perceives to be Gödel's governing ideal of philosophy: an exact theory in which mathematics and Newtonian physics serve as a model for philosophy or metaphysics. Finally, in an epilog Wang sketches his own approach to philosophy in contrast to his interpretation of Gödel's outlook. (shrink)

Werner Heisenberg: Der Teil und das Ganze.

Stem cells are defined as having capacities for both self-renewal and differentiation. Many different entities satisfy this working definition. I show that this general stem cell concept is relative to a cell lineage, temporal duration, and characters of interest. Experiments specify values for these variables. So claims about stem cells must be understood in terms of experimental methods used to identify them. Furthermore, the stem cell concept imposes evidential constraints on interpretation of experimental results. From these constraints, it follows that (...) claims about stem cell capacities are inherently uncertain. This result has important implications for stem cell research. (shrink)

The contributions of few contemporary scientists have been as far reaching in their effects as those of Nobel Laureate Werner Heisenberg.

Presents German physicist Werner Heisenberg's 1958 text in which he discusses the philosophical implications and social consequences of quantum mechanics and other physical theories.

Sommaire: Tradition ancienne et tradition nouvelleHistorique de la théorie des quantaL'interprétation de CopenhagueLa théorie quantique et les racines de la science atomiqueLe développement des idées philosophiques depuis Descartes et la nouvelle situation en théorie quantiqueRapports entre la théorie quantique et les autres sciences expérimentalesThéorie de la relativitéCritiques et contre-propositions à l'interprétation de CopenhagueThéorie quantique et structure de la matièreLangage et réalité en physique actuelleRôle de la physique moderne dans l'évolution actuelle de la pensée humaine.

This second book in the 'Middle Way Philosophy' series develops five general principles that are distinctive to the universal Middle Way as a practical response to absolutization. These begin with the consistent acknowledgement of human uncertainty (scepticism), and follow through with openness to alternative possibilities (provisionality), the importance of judging things as a matter of degree (incrementality), the clear rejection of polarised absolute claims (agnosticism) and the cultivation of cognitive and emotional states that will help us resolve conflict (...) (integration). (shrink)

It is shown that the uncertainty principle has nothing directly to do with the non-localisability of position and momentum for an individual system on the quantum logical view. The product Δ x· Δ p for localisation of the ranges of position and momentum of an individual system→ ∞ , while the quantities Δ X and Δ P in the uncertainty principle $\Delta X\cdot \Delta P\geq \hslash /2$ , must be given a statistical interpretation on the quantum (...) logical view. (shrink)

We show that the strong form of Heisenberg’s inequalities due to Robertson and Schrödinger can be formally derived using only classical considerations. This is achieved using a statistical tool known as the “minimum volume ellipsoid” together with the notion of symplectic capacity, which we view as a topological measure of uncertainty invariant under Hamiltonian dynamics. This invariant provides a right measurement tool to define what “quantum scale” is. We take the opportunity to discuss the principle of the (...) symplectic camel, which is at the origin of the definition of symplectic capacities, and which provides an interesting link between classical and quantum physics. (shrink)

In this paper, the main outlines of the discussions between Niels Bohr with Albert Einstein, Werner Heisenberg, and Erwin Schrödinger during 1920–1927 are treated. From the formulation of quantum mechanics in 1925–1926 and wave mechanics in 1926, there emerged Born's statistical interpretation of the wave function in summer 1926, and on the basis of the quantum mechanical transformation theory—formulated in fall 1926 by Dirac, London, and Jordan—Heisenberg formulated the uncertainty principle in early 1927. At the Volta (...) Conference in Como in September 1927 and at the fifth Solvay Conference in Brussels the following month, Bohr publicly enunciated his complementarity principle, which had been developing in his mind for several years. The Bohr-Einstein discussions about the consistency and completeness of qnautum mechanics and of physical theory as such—formally begun in October 1927 at the fifth Solvay Conference and carried on at the sixth Solvay Conference in October 1930—were continued during the next decades. All these aspects are briefly summarized. (shrink)

The beginning of the journey -- What this book is about : using ideas from mathematics, economics, and physics to tackle the big questions in philosophy : what is real? what can we know? what is the difference between right and wrong? and how should we live? -- Reality and unreality -- On what there is -- Why is there something instead of nothing? the best answer I have : mathematics exists because it must and everything else exists because (...) it is made of mathematics, with an excursion into artificial intelligence -- Unfinished business -- Unfinished business from chapter two : the nature and purpose of economic models -- How Richard Dawkins got it wrong -- Why Dawkins's argument against intelligent design can't be right and a mathematical analysis of the arguments for the existence of God -- Belief -- Daydream believers -- Most beliefs are ill-considered because most false beliefs are costless to hold -- The next several chapters will explore the consequences of this observation before we return to the question of where our beliefs and knowledge come from -- Unfinished business -- Unfinished business from the preceding chapter : how color vision works, sound, and water waves, the sheer craziness of economic protectionism -- Do believers believe? -- Our ill-considered beliefs about religion : why I believe that almost nobody is deeply religious -- On what there obviously is -- Our ill-considered beliefs about free will, ESP, and life after death -- Diogenes's nightmare -- How is legitimate disagreement possible if you're arguing with someone who is as intelligent and informed as you are, shouldn't you put just as much weight on your opponent's arguments as your own? -- The fact that we persist in disagreeing is strong evidence that we don't really care what's true -- Knowledge -- Knowing your math -- Where mathematical knowledge comes from and logic and why evidence and logic are not enough -- Unfinished business -- Unfinished business from the preceding chapter : the tale of hercules and the hydra, with an excursion into the lore of very large numbers -- Incomplete thinking -- Godel's incompleteness theorem and what it doesn't say about the limits of human knowledge -- The rules of logic and the tale of a Potbellied pig -- The power of logical thought, with excursions into the most counterintuitive theorem in all of mathematics and the tale of a potbellied pig -- The rules of evidence -- What we can and can't learn from evidence, with excursions into the value of preschool and how internet porn prevents rape -- The limits to knowledge -- What physics does and doesn't tell us about what we can and cannot know -- Understanding Heisenberg's uncertainty principle -- Unfinished business -- The oddness of the quantum world and why it matters to game theorists -- Right and wrong -- Telling right from wrong -- Some hard questions about right and wrong and about life and death -- The economist's golden rule -- A rule of thumb for good behavior -- How to be socially responsible -- Putting the rule of thumb into practice -- On not being a jerk -- Goofus and gallant on immigration policy -- The economist on the playground -- Our ill-considered beliefs about fairness in the market place and in the voting booth, contrasted with our carefully considered beliefs about fairness on the playground -- Unfinished business -- How ancient talmudic scholars anticipated modern economic theory -- The life of the mind -- How to think -- Some basic rules for clear thinking, mostly about economics, but also about arithmetic, neurobiology, sin, and eschewing blather -- What to study -- Advice to college students : stay away from the English department and approach the philosophy department with caution, with an excursion into the remarkable life of Frank Ramsey. (shrink)

The arguments presented by Gibbins in his Note are based on a sharp distinction between the product Δx·Δp, which refers to the ranges of position and momentum of an individual system, and the uncertainty principle ΔX·ΔP ≥ ħ/2, which expresses a statistical relation for an ensemble of systems. A critical role in Gibbins’ reasoning is played by the theorem T which states that the restriction of the dynamical variable of position x of an individual system to a finite (...) range Δx excludes the possibility of restricting the canonically conjugate dynamical variable of momentum p to a finite range Δp. (shrink)

Since the 20th century the quantum physics has shown various phenomena, judged as “seldom and not easily understandable” by the theories of classic physics. From the beginning of the “Kopenhagener Deutung,” Einstein claimed against Heisenberg, Bohr, etc. that the particle physics lacks “physical reality.” A number of physicists have tried to clarify the labyrinth of particle as a minimal substance in the phenomena of the micro world. The entanglement of the “double particle” emitted from a π-meson in its teleportation (...) is one of those phenomena. However, a successful new thesis has also become a target for the antithesis by deputies. Even if the “uncertainty” of an emitted light quantum that is received by the detector “either as a particle or as wave” has been reduced in our time by using probability calculations and new experimental physical facilities, the principal character of particles based on the “uncertainty relation” has not been changed. Although Heisenberg’s formula of the uncertainty relation could be “renewed” by completing certain operational components substituted by some physicists, the fundamental reality of phenomena of particle physics remain: The “physical reality” manifested by Einstein based on his glorious success of the Special and General Theory of Relativity cannot be valid in the micro-world phenomena.Pietschmann, a well-known theoretical physicist in Vienna, and Hashi, a philosopher teaching and researching interdisciplinary philosophy in Vienna, highlight the essential problems of particle physics and clarify them in regards to ontological and epistemological aspects. The dialogue has its origin in the hypothesis that the particle physics needs a logical interpretation with completely new ontological principles. In addition, the fundamental ontology of Mahayana Buddhist philosophy and its further development to rational philosophy of East Asia has various indications and contributions for an ontological epistemology of particle physics. (shrink)

Werner Heisenberg's 1925 paper ‘Quantum-theoretical re-interpretation of kinematic and mechanical relations’ marks the beginning of quantum mechanics. Heisenberg famously claims that the paper is based on the idea that the new quantum mechanics should be ‘founded exclusively upon relationships between quantities which in principle are observable’. My paper is an attempt to understand this observability principle, and to see whether its employment is philosophically defensible. Against interpretations of ‘observability’ along empiricist or positivist lines I argue that (...) such readings are philosophically unsatisfying. Moreover, a careful comparison of Heisenberg's reinterpretation of classical kinematics with Einstein's argument against absolute simultaneity reveals that the positivist reading does not fit with Heisenberg's strategy in the paper. Instead the appeal to observability should be understood as a specific criticism of the causal inefficacy of orbital electron motion in Bohr's atomic model. I conclude that the tacit philosophical principle behind Heisenberg's argument is not a positivistic connection between observability and meaning, but the idea that a theory should not contain causally idle wheels. (shrink)