Abstract Quantum theory and the special theory of relativity emerged almost simultaneously. Through the formative years of quantum theory, from 1900 to about 1928, arguments based on the theory of relativity were of great importance. Starting with Sommerfeld's theory of the hydrogen atom, this paper surveys the ways in which the two fundamental theories have interacted. Relativity was of particular importance in Schrödinger's route to wave mechanics, a theory which was originally conceived as fully integrated with special relativity. The problem of uniting, or harmonising, quantum mechanics and relativity continued to occupy physicists in 1926–27. The paper ends with the solution of this problem, as it was presented in 1928 by Dirac in his seminal paper on the quantum theory of electrons. It also refers to the few attempts there were in the period to formulate a quantum theory in agreement with the general theory of relativity.
Abstract Quantum theory and the special theory of relativity emerged almost simultaneously. Through the formative years of quantum theory, from 1900 to about 1928, arguments based on the theory of relativity were of great importance. Starting with Sommerfeld's theory of the hydrogen atom, this paper surveys the ways in which the two fundamental theories have interacted. Relativity was of particular importance in Schrödinger's route to wave mechanics, a theory which was originally conceived as fully integrated with special relativity. The problem of uniting, or harmonising, quantum mechanics and relativity continued to occupy physicists in 1926–27. The paper ends with the solution of this problem, as it was presented in 1928 by Dirac in his seminal paper on the quantum theory of electrons. It also refers to the few attempts there were in the period to formulate a quantum theory in agreement with the general theory of relativity.
Quantum theory and the special theory of relativity emerged almost simultaneously. Through the formative years of quantum theory, from 1900 to about 1928, arguments based on the theory of relativity were of great importance. Starting with Sommerfeld's theory of the hydrogen atom, this paper surveys the ways in which the two fundamental theories have interacted. Relativity was of particular importance in Schrödinger's route to wave mechanics, a theory which was originally conceived as fully integrated with special relativity. The problem of uniting, or harmonising, quantum mechanics and relativity continued to occupy physicists in 1926–27. The paper ends with the solution of this problem, as it was presented in 1928 by Dirac in his seminal paper on the quantum theory of electrons. It also refers to the few attempts there were in the period to formulate a quantum theory in agreement with the general theory of relativity.
The early twentieth century saw two major revolutions in the way physicists understand the world. One was quantum mechanics itself and the other was the theory of relativity. Important results also emerged when these two ideas were brought together: some of these have been referred to in earlier chapters-in particular the fact that fundamental particles such as electrons have intrinsic angular momentum (spin) was stated to be a relativistic effect. This chapter explores the relationship between relativity and quantum mechanics more deeply A full understanding of relativistic quantum mechanics is well outside the scope of this book, but many of the important results can be understood at this level and these will be discussed in this chapter. After a short summary of the main results of special relativity, we show how combining this with the time-dependent Schro¨dinger equation leads to a new wave equation known as the Dirac equation. We show how the Dirac equation requires particles such as electrons to have intrinsic angular momentum (spin) and we explore some of its other consequences. The chapter concludes with an outline of some more advanced ideas known as quantum field theory.
The year 2025 marked the centennial of quantum mechanics, inaugurated by Heisenberg's matrix formulation and the foundational contributions of Pauli, Schrodinger, and Dirac. Concurrently, 2026 marks the centennial of the Klein - Gordon equation, the second-order relativistic wave equation from which both the Schrodinger and Dirac equations were derived. This article supplements the recent review published in J.Phys. A: Math.Theor.,58 (2025) 053001 by providing a more detailed examination of the formative period 1925 - 1928, with particular attention to contributions that have received insufficient recognition in the standard narrative. We reconstruct Kramers' independent derivation of the Dirac equation - obtained essentially simultaneously with Dirac's own result yet unpublished for seven years - and discuss its relation to Van der Waerden's group-theoretical approach. The role of Charles Galton Darwin in elucidating the physical content of the Dirac equation is also highlighted. In addition, we present two modern derivations not catalogued in the earlier review: one based on Operational Dynamical Modeling, which deduces the Dirac equation from relativistic Ehrenfest relations and the canonical commutation algebra, and one rooted in the Madelung hydrodynamic formulation. Three broad periods of quantum theory development -- foundational, consolidation, and the modern era of quantum information -- are briefly surveyed.
Abstract Ontology is integral to the two most fundamental scientific theories of the twentieth century: quantum theory and the special and general theories of relativity. Issues that drove the development of quantum theory include the reality of quanta, the simultaneous wave- and particle-like nature of matter and energy, determinism, probability and randomness, Schrodinger’s wave equation, and Heisenberg’s uncertainty principle. So did the reality of the predictions about space, time, matter, energy, and the universe itself that were deduced from the special and general theories of relativity. Dirac’s prediction of antimatter based solely on the mathematics of his theory of the electron and Pauli’s prediction of the neutrino based on his belief in quantum mechanics are cases in point. Ontological interpretations of the uncertainty principle, of quantum vacuum energy fields, and of Schrodinger’s probability waves in the form of multiple universe theories further illustrate this point.
Along with the exciting experiments that changed the face of physics in the twentieth century, work proceeded feverishly on the theoretical side to rebuild the conceptual world that had been severely shaken. Sometimes the theorists lagged behind the experimentalists, and certain experimental results waited for several years to be explained. And sometimes experiment lagged behind theory, and a new theoretical model waited for years to be verified experimentally. Two great theories left their mark on physics in this century: the theory of relativity, and quantum mechanics. In this chapter we shall briefly review the main ideas of these theories which are vital for the understanding of the atomic world. The theory of relativity The theory of relativity was formulated by the great physicist Albert Einstein. The first part of it (and the important one for us) — the special theory of relativity — was published in 1905, and sprang from the need to explain a puzzling question that exercised the physicists of the nineteenth century: why was it impossible to alter the speed of light, which remained constant (299 792.5 kilometres per second) even when the detector was moving relative to the source of light? In contrast to other physicists, Einstein did not try to explain this phenomenon.
This paper takes a look at the two cornerstones of modern physics--Quantum Mechanics and The Theory of Relativity (Both Special and General). The differences and similarities for the two subjects are presented. More of their differences and similarities will emerge with new developments in physics. One can't rule out the possibility of the two being unified into one one fine day. That will herald another triumphant moment in physics. Introduction In 1905, Albert Einstein at the age of twenty-six formulated single-handedly, among others, the Theory of Special Relativity together with his other seminal papers on photoelectricity, Brownian motions of atoms and molecular dimensions. The year has been universally declared the Miraculous Year [1]. Ten years later, he came up with the theory of General Relativity--a new and revolutionary framework on gravity. Meanwhile in Europe a group of young physicists played pivotal role in the birth of Quantum Mechanics. Many of them went on to win Nobel prizes for their monumental contributions. Einstein also won the coveted prize not for Relativity but ironically for Photoelectric Effect. Irony has been part of physics in its history. Relativity with its weird 'Twin Paradox', constancy of the speed of light and the interchangebility between mass and energy (E=[mc.sup.2]) enthralls the public and scientists alike. It provides a way to measure particle masses [2]. The Quantum Theory has its fair share of weirdness and bewilderment. Both Quantum Mechanics and the Theory of Relativity bring forth new ideas in human thoughts. They are among Joanne Baker's 50 physics ideas [3]. Quantum Mechanics and the Theory of Relativity The quantum world where counterintuition reigns supreme is couched in uncertainty as epitomised by Heisenberg's uncertainty principle. Things do not behave in a deterministic way as enshrined and expected in classical Newtonian physics. The microscopic world of the electrons was dictated by randomness and indeterminacy. Albert Einstein was appalled by such dictates that he famously declared: 'God does not play dice with the universe.' The famous Danish physicist Neils Bohr sprang to his feet by saying: 'Stop telling God what to do with his dice.' The sparring between the two stalwarts in physics is legendary. According to Trefil [4], there are a couple of things that need to be said about the uncertainty principle: it does not imply that we cannot know either the position or the velocity of a particle, and it does not require the presence of a conscious mind. Marcus Chown [5] wraps up by saying 'The bitter irony, not lost on Einstein, was that he was the one who, by postulating the existence of the photon, had inadvertently set loose the genie of randomness of physics. The two theories of relativity by Einstein are not couched in randomness however. According to Smoot [6], both implied a radically new cosmology. Many people are of the opinion that with Einstein's theory of relativity, old classical physics is no more in vogue. According to Angier [7], Albert Einstein did not prove that Isaac Newton was wrong. Instead, he showed that Newton's theories of motion and gravity were incomplete, and that new equations were needed to explain the behavior of objects under extreme circumstances, such as when tiny particles travel at or near the speed of light. …