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Crisis: The End of the Bohr Model

Helge Kragh

in Niels Bohr and the Quantum Atom: The Bohr Model of Atomic Structure 1913–1925

Failed attempts to understand the anomalous Zeeman effect contributed to the feeling of crisis that by 1924 characterized parts of the physics community. The solution proposed by W. Heisenberg’s ... More

Failed attempts to understand the anomalous Zeeman effect contributed to the feeling of crisis that by 1924 characterized parts of the physics community. The solution proposed by W. Heisenberg’s ‘core model’ only raised other problems. Another indication was the state of radiation theory and the uncertain relationship between wave theory and the light quantum, a problem that resulted in the controversial BKS (Bohr–Kramers–Slater) theory of 1924. In the wake of this theory, H. Kramers and Heisenberg constructed a formal theory of dispersion that did not rely on electron orbits but only on observable quantities, in agreement with the ‘quantum mechanics’ programme of M. Born. The development culminated with Heisenberg’s paper of August 1925, which marks the end of the Bohr model and the beginning of quantum mechanics. The chapter reconsiders the crisis and the reasons for it, in particular the role of experimental anomalies.Less

What the Physicist said to the Poet: How Physicists Used the Ideal of Poetry to Talk about Uncertainty

Peter Middleton

in Physics Envy: American Poetry and Science in the Cold War and After

The chapter shows how postwar poets encountered strong negative or idealized images of poetry in the writings of physicists and other scientists. Physicists sometimes referred to an abstraction of ... More

The chapter shows how postwar poets encountered strong negative or idealized images of poetry in the writings of physicists and other scientists. Physicists sometimes referred to an abstraction of poetry in order to negotiate tricky questions about how to communicate the strangeness and “semi-phenomenological” character of the quantum world. Murray Gell-Mann coins the term “quark” partly because the allusion to Joyce enables him to finesse the questionable actuality of these sub-atomic particles. The chapter discusses the surprising prevalence of articles about poetry in general science journals aimed at professional scientists, and looks in detail at one article on contemporary poetry and science. Many poets read and referred to popular writings by Erwin Schröger and Werner Heisenberg. The chapter explains how their books appealed to poets because they referenced poetry, and talked about its possible future roles in relation to physics. Robert Creeley and Robert Duncan both found uses for the ideas of these physicists in their essays and poems. The chapter concludes with a discussion of how late in his career Oppenheimer reversed his earlier endorsement of Paul Dirac’s dismissal of poetry, by arguing that good scientific communication to the public would have the quality of lyric.Less

1937

Werner Heisenberg and Elisabeth Heisenberg

Anna Maria Hirsch-Heisenberg (ed.)

in My Dear Li: Correspondence, 1937-1946

This chapter recounts the weeks leading up to the wedding of Werner Heisenberg and Elisabeth Schumacher, from March 15 to April 26 of the year 1937. The letters from their period of engagement reveal ... More

This chapter recounts the weeks leading up to the wedding of Werner Heisenberg and Elisabeth Schumacher, from March 15 to April 26 of the year 1937. The letters from their period of engagement reveal the couple’s anticipation and preparation for married life in Leipzig. They also mark the beginnings of their mutual correspondence which would last until some time after the end of World War II. The chapter also features a brief letter from Werner to his mother on the matter of his engagement, discussing the chemistry between himself and Elisabeth after having met each other only fourteen days before this correspondence. According to Werner, their “mutual understanding…soon went so deep that it seemed natural […] to ask Elisabeth whether she would like to be with [him] forever.” They would later marry in Berlin on April 29.Less

Heisenberg, Bohr, Robertson, and the Uncertainty Principle: The Interpretation of Quantum Uncertainty

Jim Baggott

in The Quantum Cookbook: Mathematical Recipes for the Foundations for Quantum Mechanics

From the outset, Heisenberg had resolved to eliminate classical space-time pictures involving particles and waves from the quantum mechanics of the atom. He had wanted to focus instead on the ... More

From the outset, Heisenberg had resolved to eliminate classical space-time pictures involving particles and waves from the quantum mechanics of the atom. He had wanted to focus instead on the properties actually observed and recorded in laboratory experiments, such as the positions and intensities of spectral lines. Alone in Copenhagen in February 1927, he now pondered on the significance and meaning of such experimental observables. Feeling the need to introduce at least some form of ‘visualizability’, he asked himself some fundamental questions, such as: What do we actually mean when we talk about the position of an electron? He went on to discover the uncertainty principle: the product of the ‘uncertainties’ in certain pairs of variables—called complementary variables—such as position and momentum cannot be smaller than Planck’s constant h (now h / 4π‎).Less

Transitions: From the German Threat to the Soviet Menace

Vince Houghton

in The Nuclear Spies: America's Atomic Intelligence Operation against Hitler and Stalin

The fourth chapter discusses the American intelligence shift in focus from the German atomic bomb program to the atomic research effort of the Soviet Union. Alsos scientists were eventually convinced ... More

The fourth chapter discusses the American intelligence shift in focus from the German atomic bomb program to the atomic research effort of the Soviet Union. Alsos scientists were eventually convinced that the German atomic bomb program was far behind that of the United States, and would not be a factor in the Second World War. However, Alsos was kept in Europe to ensure that the Soviet Union did not gain access to German atomic resources. This meant capturing German scientists, occupying German research facilities and laboratories, and capturing German raw materials and industrial centers. In some cases, when it became apparent that Allied forces would not be able to reach certain areas before Soviet forces arrived, Groves utilized the conventional forces of the U.S. Army and the covert forces of the OSS to destroy the resource to ensure it could not be of benefit to the Soviets.Less

Visualizability and Intelligibility: Insight Into the Quantum World

Henk W. de Regt

in Understanding Scientific Understanding

This chapter investigates the relation between visualizability and intelligibility, by means of an in-depth study of the transition from classical physics to quantum physics in the first decades of ... More

This chapter investigates the relation between visualizability and intelligibility, by means of an in-depth study of the transition from classical physics to quantum physics in the first decades of the twentieth century. In this development, the issue of visualizability played a central role. After a brief discussion of the visualizability of classical physics, it examines the gradual loss of visualizability in quantum theory, focusing on the work of quantum physicists Niels Bohr, Wolfgang Pauli, Werner Heisenberg, and Erwin Schrödinger. The chapter presents a detailed analysis of the role of visualizability (Anschaulichkeit) in the competition between Schrödinger’s wave mechanics and Heisenberg’s matrix mechanics, and in the discovery of electron spin. The contextual theory of understanding asserts that visualizability is one out of many possible tools for understanding, albeit one that has proved to be very effective in science. This conclusion is supported by an analysis of the role of visualization in postwar quantum physics, especially via Feynman diagrams.Less

New Timer: Finding Mr. Heisenberg Instead

Dale Maharidge

in Someplace Like America: Tales from the New Great Depression

In this chapter, the authors discuss moral questions they apply each time they commit an act of journalism that goes beyond the basic “who, what, when, where, and why.” The moral question comes down ... More

In this chapter, the authors discuss moral questions they apply each time they commit an act of journalism that goes beyond the basic “who, what, when, where, and why.” The moral question comes down to an equation that might be described as a social cost-benefit analysis. Their motive for traveling with a human being who had been damaged by the economy, in so fragile a state, was to use his story of quest and struggle to inform the larger world so that attitudes and policies might change, that may place a value on the worth of what they did. Maybe Werner Heisenberg's Uncertainty Principle was incomplete as it applies to journalism: yes, the act of observing someone or some event changes the observed, but perhaps the observer must change as well.Less

Critique of the Standard Interpretation

Bas C. van Fraassen

in Quantum Mechanics: An Empiricist View

Von Neumann's unification of Schroedinger's and Heisenberg's formalisms came with an interpretation of quantum theory involving two principles. The first is that assertions about the values of ... More

Von Neumann's unification of Schroedinger's and Heisenberg's formalisms came with an interpretation of quantum theory involving two principles. The first is that assertions about the values of observables are equivalent to assertions about the quantum‐mechanical state of the system. This is sometimes known as the ’eigenvalue–eigenstate link’, since it equates an observable having a value with the system being in an eigenstate of that observable. The second is his Projection Postulate—i.e. the postulate that during measurement there is a ’collapse of the wave packet’. It is argued that the theory does not force these principles on us, and that there are severe difficulties in this interpretation, despite also its more recent defences.Less

Introductory Considerations

John von Neumann

Nicholas A. Wheeler (ed.)

in Mathematical Foundations of Quantum Mechanics: New Edition

This chapter presents the origins of the transformation theory and related concepts. It shows how, in 1925, a procedure initiated by Werner Heisenberg was developed by himself, Max Born, Pascual ... More

This chapter presents the origins of the transformation theory and related concepts. It shows how, in 1925, a procedure initiated by Werner Heisenberg was developed by himself, Max Born, Pascual Jordan, and a little later by Paul Dirac, into a new system of quantum theory—the first complete system of quantum theory which physics has possessed. A little later Erwin Schrödinger developed the “wave mechanics” from an entirely different starting point. This accomplished the same ends, and soon proved to be equivalent to the Heisenberg, Born, Jordan, and Dirac system. On the basis of the Born statistical interpretation of the quantum theoretical description of nature, it was possible for Dirac and Jordan to join the two theories into one, the “transformation theory,” in which they make possible a grasp of physical problems which is especially simple mathematically.Less

Unheard Harmonies

Peter Pesic

in Music and the Making of Modern Science

Among early twentieth-century physicists, many considered their musical experiences formative of their relation to science. Albert Einstein’s famous devoted to music seems linked to his scientific ... More

Among early twentieth-century physicists, many considered their musical experiences formative of their relation to science. Albert Einstein’s famous devoted to music seems linked to his scientific work mainly through a general quest for harmony. Werner Heisenberg was a skilled musician who embraced a Platonic search for cosmic order after a revelatory performance of Bach. Even the unmusical Erwin Schrödinger found himself relying on musical analogies (as well as color theory) when he formulated his wave mechanics. The development of string theory reengages the mathematics of vibration, though the reality of the “strings” rests on analogy built on analogy, as shown in the progression Yoichiro Nambu described in his early work on this theory. Indeed, the concept of resonance remains important throughout physics, such as high-energy experiments. The Pythagorean theme of harmony remains potent in contemporary physics, though its harmonies are more and more unhearable and embedded in mathematical formalism. Throughout the book where various sound examples are referenced, please see http://mitpress.mit.edu/musicandmodernscience (please note that the sound examples should be viewed in Chrome or Safari Web browsers).Less

Von Neumann and the Problem of Quantum Measurement: The ‘Collapse of the Wavefunction’

Jim Baggott

in The Quantum Cookbook: Mathematical Recipes for the Foundations for Quantum Mechanics

Heisenberg was an ‘anti-realist’. Although Bohr was infamously obscure in many of his writings, it seems that he adopted a generally anti-realist interpretation, too. As their debate became more ... More

Heisenberg was an ‘anti-realist’. Although Bohr was infamously obscure in many of his writings, it seems that he adopted a generally anti-realist interpretation, too. As their debate became more bitter, in early June 1927 Pauli was called in to mediate. With Pauli’s help, they forged an uneasy consensus, which became known as the Copenhagen interpretation. Einstein didn’t like it at all, setting the stage for a great debate about the quantum representation of reality. Although von Neumann’s formalism broadly conforms to the Copenhagen interpretation, he saw no need to introduce an arbitrary split between the classical and quantum worlds. But eliminating the split poses the problem of quantum measurement: when scaled to classical dimensions, a superposition of different measurement outcomes appears contrary to our experience, exemplified by the famous paradox of Schrödinger’s cat. Von Neumann was obliged to break the infinite regress by postulating the ‘collapse of the wavefunction’.Less

Empirical: The Physical Sciences

Peter V. Rabins

in The Why of Things: Causality in Science, Medicine, and Life

This chapter discusses three concepts, developed during the twentieth century, that have significantly influenced the current conceptualization of causality: relativity theory, quantum mechanics, and ... More

This chapter discusses three concepts, developed during the twentieth century, that have significantly influenced the current conceptualization of causality: relativity theory, quantum mechanics, and the incompleteness theorem. It also examines how a series of discoveries in the physical science of geology led to the development of plate tectonic theory and how it became widely accepted as the primary causal explanation for geologic phenomena such as continental drift. In addition, it covers three key concepts: first, there are limits to the knowledge one can gain no matter what techniques are used; second, more than one approach or vantage point is sometimes necessary to identify causal influences with as much accuracy as possible; and third, in many complex physical systems, causality results from the interaction of multiple elements rather than from the interaction of two individual events. Finally, it considers Werner Heisenberg's uncertainty principle and the wave/particle duality of light.Less