arXiv subjects

Helge Kragh

Publications and source records attributed to Helge Kragh.

At least 19 recordsLinked to original sources

arXiv2026

Erwin Schroedinger: His Poetry and Fragment of a Galilean Dialogue

While Erwin Schroedinger's contributions to quantum mechanics and other areas of theoretical physics are very well known, his works as a poet and literary writer are usually ignored. In this paper I reconsider his poetry and refer to a few poems written about him. A short fragment of a Galileo-inspired dialogue that Schroedinger published in 1955 is as interesting as it is puzzling and little known. The dialogue is essentially about atomic theory as known much earlier, namely in the early 1910s. Indeed, there is the slight possibility that Schroedinger may originally have conceived it at that time and even composed a version of it. Apart from considering the origin and reception of the manuscript, I analyze its content from the point of view of the history of physics.

physics.hist-ph↗

arXiv2025

Tachyons Before Tachyons: Lev Strum (1890-1936) and Superluminal Velocities

No particle or signal carrying information can travel at a speed exceeding that of light in vacuum. Although this has for a long time been accepted as a law of nature, prior to Einstein's 1905 theory of special relativity the possibility of superluminal motion of electrons was widely discussed by Arnold Sommerfeld and other physicists. Besides, it is not obvious that special relativity rules out such motion under all circumstances. From approximately 1965 to 1985 the hypothesis of tachyons moving faster than light was seriously entertained by a minority of physicists. This paper reviews the early history concerning superluminal signals and pays particular attention to the ideas proposed in the 1920s by the little known Ukrainian physicist Lev Strum (Shtrum). As he pointed out in a paper of 1923, within the framework of relativity it is possible for a signal to move superluminally without violating the law of causality. Part of this article is devoted to the personal and scientific biography of the undeservedly neglected Strum, whose career was heavily and eventually fatally influenced by the political situation in Stalin's Russia. Remarkably, to the limited extent that Strum is known today, it is as a literary figure in a novel and not as a real person.

physics.hist-ph↗

arXiv2023

Anticipations and Discoveries of the Heavy Hydrogen Isotopes, 1913-1939

Just as the chemical elements from hydrogen (Z = 1) to oganesson (Z = 118) once were discovered, so were the numerous isotopes. The histories of how the isotopes were discovered are less well known, but in a few cases they are as interesting and instructive as those of the elements figuring in the periodic table. Following an overview of criteria usually associated with the concept of discovery in general, this paper examines in detail the historical developments that led to the discoveries of deuterium and tritium and also, as a by-product, the helium-3 isotope. It also includes a brief section on the neutron, which in the 1920s, when it was still a hypothetical particle, was sometimes discussed together with the mass-2 and mass-3 hydrogen isotopes. The paper concludes with a discussion of priority questions relating to suggestions of the two heavy isotopes as well as to their actual discoveries.

physics.hist-ph↗

arXiv2022

Before Bethe: Early Ideas of the Sun's Generation of Energy

Solar energy remained an enigma for nearly a century. For a while astronomers and physicists believed that the source of the Sun's energy was gravitational contraction, but the theory turned out to be untenable. Inspired by the new science of radioactivity, by the early twentieth century they increasingly focused on subatomic processes. The paper outlines the attempts to solve the solar energy problem in the period from about 1905 to 1938, which in the later phase involved nuclear astrophysics, a new and exciting interdisciplinary science. Although the problem was only satisfactorily solved with Hans Bethe's theory of the late 1930s, the earlier attempts involving scientists such as Arthur Eddington, Robert Atkinson and George Gamow can be considered a slow preparation for Bethe's breakthrough.

physics.hist-ph↗

arXiv2021

Reluctant Pioneer of Nuclear Astrophysics: Eddington and the Problem of Stellar Energy

During the years from 1917 to 1921, A.S. Eddington was intensely occupied with Einstein's general theory of relativity and the epic eclipse expedition which confirmed one of the theory's predictions. During the same period, he investigated the old problem of why the stars shine, which led him to suggest two different subatomic mechanisms as the source of stellar energy. One of them was the annihilation of matter and the other the building-up of helium from hydrogen. This paper is concerned with Eddington's work in this area, a line of work to which he returned on and off during the 1920s but then abandoned. His decision to stop working on the stellar energy problem coincided with the first attempts to understand the problem in terms of nuclear physics and quantum mechanics. Why did Eddington not follow up his earlier work and why did he ignore the contributions of the nuclear physicists which in the late 1930s resulted in the first successful theories of stellar energy production?

physics.hist-ph↗

arXiv2019

Physics and the Totalitarian Principle

What is sometimes called the "totalitarian principle," a metaphysical doctrine often associated with the famous physicist Murray Gell-Mann, states that everything allowed by the laws of nature must actually exist. The principle is closely related to the much older "principle of plenitude." Although versions of the totalitarian principle are well known to physicists and often appear in the physics literature, it has attracted little reflection. Apart from a critical examination of the origin and history of the totalitarian principle, the paper discusses this and the roughly similar plenitude principle from a conceptual perspective. In addition it offers historical analyses of a few case studies from modern physics in which reasoning based on the totalitarian principle can be identified. The cases include the prediction of the magnetic monopole, the hypothesis of radioactive protons, and the discovery of the muon neutrino. Moreover, attention is called to the new study of metamaterials.

physics.hist-ph↗

arXiv2019

Max Weinstein: Physics, Philosophy, Pandeism

This is a brief introduction to the life and ideas of the Lithuanian-German physicist, philosopher and religious thinker Max B. Weinstein, who is today best known for his thoughts concerning so-called pandeism. An accomplished theoretical physicist and characteristic figure in the fin-de-siecle transition of the physical world view, Weinstein contributed to a wide range of physics. He was an early if not unsympathetic critic of Einstein's theory of relativity and Minkowski's formulation of it. In this respect he was unoriginal, but in the broader context of science and humanist culture he was an original thinker. He argued in favour of what he called pandeism, a religious-philosophical view according to which the physical world and the cosmic deity are one and the same.

physics.hist-ph↗

arXiv2018

Hubble Law or Hubble-Lemaître Law? The IAU Resolution

The Hubble law, widely considered the first observational basis for the expansion of the universe, may in the future be known as the Hubble-Lemaître law. This is what the General Assembly of the International Astronomical Union recommended at its recent meeting in Vienna. However, the resolution in favour of a renamed law is problematic in so far as concerns its arguments based on the history of cosmology in the relevant period from about 1927 to the early 1930s. A critical examination of the resolution reveals flaws of a non-trivial nature. The purpose of this note is to highlight these problems and to provide a better historically informed background for the voting among the union's members, which in a few months' time will result in either a confirmation or a rejection of the decision made by the General Assembly.

physics.hist-ph↗

arXiv2018

Ludvig Lorenz (1867) on Light and Electricity

Independent of Maxwell, in 1867 the Danish physicist L. V. Lorenz proposed a theory in which he identified light with electrical oscillations propagating in a very poor conductor. Lorenz's electrodynamic theory of light, which formally was equivalent to Maxwell's theory but physically quite different from it, was published in well-known journals in German and English but soon fell into oblivion. In 1867 Lorenz also published a paper on his new theory in a semi-popular Danish journal which has generally been overlooked. This other paper is here translated into English and provided with the necessary annotations.

physics.hist-ph↗

arXiv2017

The search for superheavy elements: Historical and philosophical perspectives

The heaviest of the transuranic elements known as superheavy elements (SHE) are produced in nuclear reactions in a few specialized laboratories located in Germany, the U.S., Russia, and Japan. The history of this branch of physical science provides several case studies of interest to the philosophy and sociology of modern science. The story of SHE illuminates the crucial notion of what constitutes a chemical element, what the criteria are for discovering a new element, and how an element is assigned a name. The story also cast light on the sometimes uneasy relationship between physics and chemistry. It is far from obvious that elements with Z > 110 exist in the same sense as oxygen or sodium exists. The answers are not given by nature but by international commissions responsible for the criteria and evaluation of discovery claims. The works of these commissions and of SHE research in general have often been controversial.

physics.hist-ph↗

arXiv2017

Cosmology and the Origin of the Universe: Historical and Conceptual Perspectives

From a modern perspective cosmology is a historical science in so far that it deals with the development of the universe since its origin some 14 billion years ago. The origin itself may not be subject to scientific analysis and explanation. Nonetheless, there are theories that claim to explain the ultimate origin or "creation" of the universe. As shown by the history of cosmological thought, the very concept of "origin" is problematic and can be understood in different ways. While it is normally understood as a temporal concept, cosmic origin is not temporal by necessity. The universe can be assigned an origin even though it has no definite age. In order to clarify the question a view of earlier ideas will be helpful, these ideas coming not only from astronomy but also from philosophy and theology.

physics.hist-ph↗

arXiv2017

Fundamental Theories and Epistemic Shifts: Can History of Science Serve as a Guide?

The present discussion concerning certain fundamental physical theories (such as string theory and multiverse cosmology) has reopened the demarcation problem between science and non-science. While parts of the physics community see the situation as a beginning epistemic shift in what defines science, others deny that the traditional criterion of empirical testability can or should be changed. As demonstrated by the history of physics, it is not the first time that drastic revisions of theory assessment have been proposed. Although historical reflection has little to offer modern physicists in a technical sense, it does offer a broader and more nuanced perspective on the present debate. This paper suggests that history of science is of some indirect value to modern physicists and philosophers dealing with string theory, multiverse scenarios, and related theoretical ideas.

physics.hist-ph↗

arXiv2016

The Source of Solar Energy, ca. 1840-1910: From Meteoric Hypothesis to Radioactive Speculations

Why does the Sun shine? Today we know the answer to the question and we also know that earlier answers were quite wrong. The problem of the source of solar energy became an important part of physics and astronomy only with the emergence of the law of energy conservation in the 1840s. The first theory of solar heat based on the new law, due to J. R. Mayer, assumed the heat to be the result of meteors or asteroids falling into the Sun. A different and more successful version of gravitation-to-heat energy conversion was proposed by H. Helmholtz in 1854 and further developed by W. Thomson. For more than forty years the once so celebrated Helmholtz-Thomson contraction theory was accepted as the standard theory of solar heat despite its prediction of an age of the Sun of only 20 million years. In between the gradual demise of this theory and the radically different one based on nuclear processes there was a period in which radioactivity was considered a possible alternative to gravitational contraction. The essay discusses various pre-nuclear ideas of solar energy production, including the broader relevance of the question as it was conceived in the Victorian era.

physics.hist-ph↗

arXiv2016

Ludvig Lorenz, Electromagnetism, and the Theory of Telephone Currents

Ludvig V. Lorenz (1829-1891) was Denmark's first theoretical physicist and the only one whose work attracted international attention in the second half of the nineteenth century. This paper presents a survey of Lorenz's contributions to physics with an emphasis on his work in electrodynamics and electrical science. His 1867 electrodynamic theory of light was of a theoretical and foundational nature, while his unpublished theory of telephone currents was oriented toward practical problems in long-distance telephony. Lorenz's theories are briefly compared to those of better known physicists such as H. A. Lorentz, J. C. Maxwell, and O. Heaviside.

physics.hist-ph↗

arXiv2015

On Arthur Eddington's Theory of Everything

From 1929 to his death in 1944, A. Eddington worked on developing a highly ambitious theory of fundamental physics that covered everything in the physical world, from the tiny electron to the universe at large. His unfinished theory included abstract mathematics and spiritual philosophy in a mix which was peculiar to Eddington but hardly intelligible to other scientists. The constants of nature, which he claimed to be able to deduce purely theoretically, were of particular significance to his project. Although highly original, Eddington's attempt to provide physics with a new foundation had to some extent parallels in the ideas of other British physicists, including P. Dirac and E. A. Milne. Eddington's project was however a grand failure in so far that it was rejected by the large majority of physicists. A major reason was his unorthodox view of quantum mechanics.

physics.hist-ph↗

arXiv2015

Expanding Earth and Static Universe: Two Papers of 1935

The German-born astronomer Jacob K. E. Halm (1866-1944) wrote in 1935 two papers on quite different subjects, one an astrophysically based argument for the expanding Earth and the other a no less original attempt to explain the galactic redshifts on the basis of a static universe. Of course, Halm was wrong in both cases. The second of the papers is reproduced in toto and compared to other early attempts to avoid the expansion of the universe by means of "tired light" explanations of the redshifts. Although often referred to in the literature on the expanding Earth, the content of Halm's first paper is not well known. This article also provides a brief account of Halm's life and scientific career, which included important studies of the solar spectrum (the "limb effect") and the first version of the mass-luminosity relation for stars.

physics.hist-ph↗

arXiv2015

Gravitation and the earth sciences: the contributions of Robert Dicke

The American physicist Robert Dicke (1916-1997) is primarily known for his important contributions to gravitation, cosmology, and microwave physics. Much less known is his work in geophysics and related areas of the earth sciences in which he engaged himself and several of his collaborators in the period from about 1957 to 1969. Much of Dicke's work in geophysics was motivated by his wish to obtain evidence in support of the non-Einstenian Brans-Dicke theory of gravitation. The idea of a decreasing gravitational constant, as entertained by Dicke and some other physicists (including Pascual Jordan), played some role in the process that transformed the static picture of the Earth to a dynamical picture. It is not by accident that Dicke appears as a minor actor in histories of the plate tectonic revolution in the 1960s.

physics.hist-ph↗

arXiv2014

Historical Aspects of Post-1850 Cosmology

Cosmology as an exact physical science is of new date, but it has long roots in the past. This essay is concerned with four important themes in the history of cosmological thought which, if taken together, offer a fairly comprehensive account of some of the key developments that have led to the modern understanding of the universe. Apart from the first section, dealing with early views of curved space, it focuses on mainstream cosmology from the expanding universe about 1930 to the emergence of the standard big bang model in the 1960s. This development includes theories we would not today consider "mainstream," such as the steady state model of the universe. The last section outlines what might be called the prehistory of the concept of dark energy, that is, ideas that were discussed before dark energy was actually inferred from supernovae observations in the late 1990s.

physics.hist-ph↗