History of Physics

Since about 1970 the broadly accepted theory of the universe has been the standard hot big-bang model. However, there is and has always been alternative theories which challenge one or more features of the standard model or, more radically, question the scientific nature of cosmology. Is the universe governed by Einstein’s field equations? Is it really in a state of expansion? Did it begin with a big bang? The chapter discusses various alternative or heterodox theories in the period from about 1930 to 1980, among them the idea of a static universe and the conception that our universe evolves cyclically in infinite cosmic time. While some of these theories have been abandoned long ago, others still live on and are cultivated by a minority of cosmologists and other scientists.

This article examines the physics of René Descartes. Descartes’ natural philosophy marks a significant moment in the larger history of physics. His system of natural philosophy was a novel, daring, and intricate construction in that field, with two main sets of historical significances for later physics. Before discussing these two significant consequences of Descartes’ natural philosophy for physics, the article provides an overview of the developmental anatomy of Cartesian physics during the period 1618–1644. In particular, it considers the successes, failures, and fate of Descartes’ early physico-mathematics programme, his work on physico-mathematical optics and corpuscular dynamics, and his career inflection between 1628 and 1633. It also explores Descartes’ ideas on vortex celestial mechanics, the explanatory style of mature Cartesian physics, and his work on classical mechanics. Finally, it looks at Descartes’ concerns with realist Copernicanism.

Observations of the cosmic microwave background (CMB) form the basis for modern ‘precision cosmology’. This chapter treats the discovery of a ≈3 K microwave background and the demonstration of its cosmic origin. Key observational results, up to and including the results from the COBE mission, follow. The major impact of the CMB comes from measurements of the power spectra of fluctuations in the temperature and polarization. The chapter ends with results derived from the power spectra obtained by the Planck mission, including values for the baryon, dark matter, and dark energy densities; the curvature of space; and the expansion rate of the Universe.

Although modern cosmology is essentially a twentieth-century science, its birth can reasonably be traced back to discussions about the universe in the previous century. With the emergence of astrophysics in the 1860s astronomy was substantially changed and the material content of the universe became an issue of science. At about the same time thermodynamics was applied to the universe at large, with the result that the beginning and end of the universe entered astronomical thought. Moreover, it became slowly realized that space can be described as curved rather than flat. In that case it would be possible to speak about a finite and yet unbounded universe and in this way to solve some of the problems associated with the traditional view of an infinite number of stars. These and other problems were only fully understood in the twentieth century, but they were discussed before Einstein revolutionized cosmology.

This article focuses on developments in electricity and magnetism up to the time of Alessandro Volta. Until the late 1600s electricity as a subject reduced to what has been aptly termed the ‘amber effect’. At the beginning of the century William Gilbert broadened the class of objects that could produce the effect and at the same time introduced a fundamental distinction between it and the properties of the lodestone, or magnet. Gilbert’s Scholastic understanding of magnetism contrasts markedly with what seems to be a quasi-mechanical understanding of electricity, the latter being more congenial to the post-Scholastic way of thinking about nature. This article first provides an overview of experiments on electric objects, including the Leiden jar, before discussing Volta’s quantification of the distinction between amount of electricity and electric tension around 1780.

This article examines developments in the field of electrodynamics from William Thomson and James Clerk Maxwell to Heinrich Hertz. It begins with a discussion of Michael Faraday’s work, focusing on his discovery of what was later termed ‘dielectric capacity’ and his role in the birth of field theory. It then considers Thomson’s unification of Faraday’s understanding of both electro- and magnetostatics with energy conservation, along with Maxwell’s extension of Thomson’s structure to cover electrodynamics, which for the first time brought to the fore issues concerning the electric current. It also describes Maxwellian electrodynamics and electromagnetic theory, Hermann Helmholtz’s development of a different form of electrodynamics, and Hertz’s work on electric waves.

This article examines developments in electromagnetism and field physics during the early nineteenth century, when electricity had become a fully respected area of research. It begins with a discussion of the ‘Volta’s pile’, an apparatus developed by Alessandro Volta, along with mathematical approaches to electricity and Hans-Christian Ørsted’s discovery of electromagnetism. It then reviews the work of André-Marie Ampère and the Biot–Savart law, introduced by Jean Baptiste Biot and Félix Savart; developments in electrodynamics during the period 1821–1826; and Michael Faraday’s research initiative in electromagnetism, and especially electromagnetic induction and the electrotonic state. It also looks at three important developments in electromagnetism during the 1820s: galvanometers, electromagnets, and Arago’s effect. Finally, it describes Lenz’s law, electromagnetic generators, the electromagnetic telegraph, the Faraday effect, diamagnetism, and the question of polarity as well as the role of mathematics in Faraday’s theories.

This article traces the history of statistical mechanics, beginning with a discussion of mechanical models of thermal phenomena. In particular, it considers how several circumstances, including the establishment of thermodynamics in the mid-nineteenth century, led to a focus on the model of heat as a motion of particles. It then describes the concept of heat as fluid and the kinetic theory before turning to gas theory and how it served as a bridge between mechanics and thermodynamics. It also explores gases as particles in motion, the Maxwell–Boltzmann distribution, the problem of specific heats, challenges to the second law of thermodynamics, and the probabilistic interpretation of entropy. Finally, it examines how the results of the kinetic theory assumed a new meaning as cornerstones of a more broadly conceived statistical physics, along with Josiah Willard Gibbs and Albert Einstein’s development of statistical mechanics as a synthetic framework.

This article focuses on the construction of the new sciences of thermodynamics and energy in Britain during the Victorian era, arguing that it occurred not simply within the broad contexts of industrialized engineering but that the new industries of marine engineering and the new sciences were, in specific local contexts on the Thames and on the Clyde, integral to one another. It begins with an account of James Thomson’s marine engineering networks centred on the Thames at Millwall, followed by a discussion on the work of his brother William at the Glasgow College laboratory. It then considers Robert Mansel’s development of an exceptionally sensitive thermometer before turning to the shipbuilding yards and marine engineering works of the Clyde at Glasgow, still in its relative infancy as the producer of the British Empire’s ocean steamers.

This article examines experimentation in the physical sciences during the seventeenth century. It first provides an overview of some features and problems of seventeenth-century experimentation before discussing experiments on the science of motion, with particular emphasis on falling bodies, the inclined plane and projectiles, and the pendulum. It then considers barometric experiments associated with Torricelli and their aftermath, including Florin Périer’s Puy-de Dôme experiment in 1648 to test whether the mercury in the barometer was lower at the top, Adrien Auzout’s void-in-the-void experiment, and Gilles de Roberval’s carp-bladder experiment. It also describes the experiments of Otto von Guericke and Robert Boyle, along with optical experiments designed to investigate the behaviour and nature of light, including Isaac Newton’s prismatic experiments.

This article focuses on the evolution and transformations of the instrument-making industry between 1850 and 1930. It begins with an overview of some broad categories of instruments, namely: research and precision measurement instruments, didactic and teaching instruments, industrial instruments, professional instruments, and scientific instruments. It then examines the history of the production of physics instruments and how workshops were organized, along with some of the techniques and materials used in the production of instruments. It also discusses the advertising, trading, and selling of instruments during the period; how instrument-makers in France, Britain, and Germany fared; the state of instrument-making from 1900 to World War I; and instrument-making in the United States and other countries in Europe. Finally, it evaluates instrument-making during the inter-war years.

This article examines Galileo’s ideas about the mechanics of natural motion and projectiles. Among the subjects in mechanics considered by Galileo, the most important are ‘natural motion’, the descent of falling bodies including on inclined planes, and the motion of projectiles under an impressed force. He also considered, and made contributions to, the resistance of solid bodies to fracture and the hydrostatics of floating bodies. What is often called ‘Platonism’ in Galileo, his appeal to mathematics and idealized conditions, is in fact the abstract mathematical analysis of mechanics. This article considers Galileo’s research and writing on falling bodies and projectiles, including his early treatise De motu, the Dialogue on the Two Great Systems of the World, the manuscript Firenze Biblioteca Nazionale Centrale Galileo Ms. 72, and the Discourses and Mathematical Demonstrations concerning Two New Sciences.

The success of the Λ CDM model has raised a number of challenging problems for the origin of structure in the universe and the initial state from which it evolved. The origins of these basic cosmological problems are described. The dark matter must be non-baryonic, but its nature has not been established. Likewise, the nature of the dark energy is not understood. The inflationary model for the very early universe has had some undoubted successes in accounting for the initial power-spectrum of fluctuations from which large-scale structures formed but there is no physical realization of the inflaton field. Defects formed during phase transitions in the early universe cannot account for the initial power spectrum of fluctuations, but may have some part to play in structure formation. The origin of the baryon-antibaryon asymmetry in the early universe is not understood in terms of theories of particle physics.

This article focuses on instruments and instrument-makers during the period 1700–1850. Scientific instruments in the 150 years between 1700 and 1850 enjoyed rapid advances in design and technology that the period can usefully be divided at about 1800, though the date varied with the progress or otherwise in the lands concerned. Throughout this period the leading craftsmen were becoming better-educated, many having a good grasp of mathematics. This article deals mainly with instruments and their makers in Britain, with a brief survey of the situation in western Europe and in the United States. It first describes the political situation in Europe before discussing the British instrument-makers’ workshop practice and materials available in the craftsmen’s workshops, including brass and other alloys, glass and wood. It also considers the British market for optical instruments and philosophical instruments, along with instrument-makers and markets in Continental Europe and the United States.

This Handbook looks at the history of physics since the seventeenth century. It is comprised of four sections, the first of which discusses the place of reason, mathematics, and experiment in the age of the scientific revolution. The first section also covers the contributions of Galileo, René Descartes, and Isaac Newton. The second section deals with the ‘long’ eighteenth century — a period that is often regarded as synonymous with the ‘age of Newton’. The third section encompasses the subcategories of heat, light, electricity, sound, and magnetism, while the fourth and final section takes us into the age of ‘modern physics’, highlighted by landmark achievements such as the discovery of the photoelectric effect in 1887, Max Planck’s work on the quanta of radiation, Albert Einstein’s special theory of relativity of 1905, and the elaboration of the various aspects of what became known as quantum physics between 1900 and 1930.

This article focuses on Pierre Simon Laplace’s contributions to the physics of short-range forces. Laplacian physics can be interpreted as an attempt to realize a supposedly Newtonian ideal of a science that would account for all phenomena in terms of attractive or repulsive central forces acting between the particles of matter. Laplace formulated and pursued a programme between the 1790s and his death in1827 based on Isaac Newton’s ideas, but it also incorporated theories with a less direct Newtonian pedigree. The most important of these were the theories of the imponderable property-bearing fluids of heat (commonly known as caloric), light, electricity, and magnetism. Laplace first engaged with questions relating to the imponderable fluids in the context of his early experimental work on heat in the 1770s. This article first discusses Laplace’s programme before considering his association with the First Class of the French Institute and his legacy.

This article examines the mutual influences between mathematics and the new sciences that emerged in the long seventeenth century, whereby new scientific enterprises fostered the development of new mathematical methods and mathematical developments in turn paved the way for new scientific research. It begins with an overview of the revolutions in mathematics in the long seventeenth century and the status of the mathematical sciences in the Late Renaissance, followed by a discussion on the work of mathematicians in the late sixteenth century including Galileo, René Descartes, Gottfried Wilhelm Leibniz, Jacob Bernoulli, Gerhard Mercator, and Edmond Halley. It also describes the work done in the areas of organic geometry and mechanical curves, infinitesimals, and mechanics.

This article focuses on mechanics in the eighteenth century. The publication in 1687 of Isaac Newton’s Mathematical Principles of Natural Philosophy has long been regarded as the event that ushered in the modern period in mathematical physics. The success and scope of the Principia heralded the arrival of mechanics as the model for the mathematical investigation of nature. This subject would be at the cutting edge of science for the next two centuries. This article first provides an overview of the fundamental principles and theorems of mechanics, including the principles of inertia and relativity, before discussing the dynamics of rigid bodies. It also considers the formulation of mechanics by Jean-Baptiste le Rond d’Alembert and Joseph-Louis Lagrange, the statics and dynamics of elastic bodies, and the mechanics of fluids. Finally, it describes major developments in celestial mechanics.

This article examines Isaac Newton’s contributions to the development of optics. Newton’s Opticks: Or, a Treatise of the Reflexions, Refractions, Inflexions and Colours of Light (1704) dominated the science of optics for more than a century. His theory of colour and the compound nature of sunlight was central to modern optics. This article first considers Newton’s reflecting telescope before discussing the fundamental elements of his theory of the nature of white light and colour. It then evaluates the reception toward Newton’s ‘new theory about light and colour’ and his refinement of the theory, along with his corpuscular optics, with emphasis on his explanation regarding refraction and dispersion. It also explores Newton’s ideas about the colours of natural bodies and of thick plates, his theory of fits, and the delayed publication of the Opticks. Finally, it reflects on Robert Hooke’s influence on Newton’s concept of diffraction.

This article examines the historical context of Isaac Newton’s Mathematical Principles of Natural Philosophy (Principia) and how it reoriented natural philosophy for generations. It first considers how the Principia extends and refines the ideas of De Motu, taking into account the three Laws of Motion, the force responsible for the planetary trajectories, the motion of projectiles in a resisting medium, and the law of universal gravitation. It then discusses three changes that influenced fundamentally the content and reception of the Principia: the relabelling and rewording of nine ‘hypotheses’ (into ‘phenomena’ and ‘rules of reasoning’) at the start of Book 3; the addition of the General Scholium; and changes that minimized explicit commitments to atomism. It also assesses the impact of the Principia on the development of physics and concludes with an overview of Newton’s theory about the cause of gravity