Background At a time when no single known fact supported this theory, Louis de Broglie asserted that a stream of electrons which passed through a very small hole in an opaque screen must exhibit the same phenomena as a light ray under the same conditions. (Prof. C. W. Oseen, Chairman of the Nobel Committee for Physics, presentation speech, 12 December 1929 (Oseen 1999)) In September 1923, Prince Louis de Brogliea made one of the most astonishing predictions in the history of theoretical physics: that material bodies would exhibit the wave-like phenomena of diffraction and interference upon passing through sufficiently narrow slits. Like Einstein's prediction of the deflection of light by the sun, which was based on a reinterpretation of gravitational force in terms of geometry, de Broglie's prediction of the deflection of electron paths by narrow slits was made on the basis of a fundamental reappraisal of the nature of forces and of dynamics. De Broglie had proposed that Newton's first law of motion be abandoned, and replaced by a new postulate, according to which a freely moving body follows a trajectory that is orthogonal to the surfaces of equal phase of an associated guiding wave. The resulting ‘de Broglian dynamics’ – or pilot-wave theory as de Broglie later called it – was a new approach to the theory of motion, as radical as Einstein's interpretation of the trajectories of falling bodies as geodesics of a curved spacetime, and as far-reaching in its implications. In 1929 de Broglie received the Nobel Prize ‘for his discovery of the wave nature of electrons’.
Background At a time when no single known fact supported this theory, Louis de Broglie asserted that a stream of electrons which passed through a very small hole in an opaque screen must exhibit the same phenomena as a light ray under the same conditions. (Prof. C. W. Oseen, Chairman of the Nobel Committee for Physics, presentation speech, 12 December 1929 (Oseen 1999)) In September 1923, Prince Louis de Brogliea made one of the most astonishing predictions in the history of theoretical physics: that material bodies would exhibit the wave-like phenomena of diffraction and interference upon passing through sufficiently narrow slits. Like Einstein's prediction of the deflection of light by the sun, which was based on a reinterpretation of gravitational force in terms of geometry, de Broglie's prediction of the deflection of electron paths by narrow slits was made on the basis of a fundamental reappraisal of the nature of forces and of dynamics. De Broglie had proposed that Newton's first law of motion be abandoned, and replaced by a new postulate, according to which a freely moving body follows a trajectory that is orthogonal to the surfaces of equal phase of an associated guiding wave. The resulting ‘de Broglian dynamics’ – or pilot-wave theory as de Broglie later called it – was a new approach to the theory of motion, as radical as Einstein's interpretation of the trajectories of falling bodies as geodesics of a curved spacetime, and as far-reaching in its implications. In 1929 de Broglie received the Nobel Prize ‘for his discovery of the wave nature of electrons’.
A physically real wave associated with any moving particle and travelling in a surrounding material medium was introduced by Louis de Broglie in a series of short notes in 1923 and in a more complete form in his thesis defended in Paris on the 25th November 1924. This result, recognised by the Nobel Prize in 1929, gave rise to a major direction of "new physics" known today as "quantum mechanics". However, although such notions as "de Broglie wavelength" and "wave-particle duality" form the basis of the standard quantum theory, it actually only takes for granted (postulates) the formula for the particle wavelength and totally ignores the underlying causal, realistic and physically transparent picture of wave-particle dynamics outlined by Louis de Broglie in his thesis and further considerably developed in his later works, in the form of "double solution" and "hidden thermodynamics" theory. A price to pay for such rough deviation from the original de Broglian realism and consistency involves fundamental physics domination by purely abstract and mechanistically simplified schemes of formal symbols and rules that have led to a deep knowledge impasse justly described as "the end of science". However, a new, independent approach of "quantum field mechanics" (quant-ph/9902015, quant-ph/9902016, physics/0401164) created within the "universal science of complexity" (physics/9806002) provides many-sided confirmation and natural completion of de Broglie's "nonlinear wave mechanics", eliminating all its "difficult points" and reconstituting the causally complete, totally consistent and intrinsically unified picture of the real, complex micro-world dynamics directly extendible to all higher levels of unreduced world complexity.
Louis-Victor de Broglie secured his place in the history of quantum physics by proposing the existence of matter waves. Following the concept accepted early in the twentieth century that light waves could display properties characteristic of particles (photons), de Broglie suggested the complementary principle that particles could display properties characteristic of waves. Within a few years, this far-reaching proposal was experimentally verified. The well-known formula for the wavelength λ of the wave associated with a particle of momentum p, namely λ=h/p, does not appear in de Broglie’s original paper, which was published in this journal in 1924. What is derived from the starting assumption that the frequency of the wave is the rest energy of the particle divided by Planck’s constant h, is the wave's velocity, which turns out to be c2/v, where v is the particle’s velocity. This velocity, being superluminal, means that the wave cannot transport energy. De Broglie called it a phase wave and postulated a group of such waves having virtually, but not exactly, the same velocity and wavelength. The group velocity of such a large number of almost identical phase waves is then shown, very satisfactorily, to be equal to the velocity of the particle. The proposal by de Broglie inspired Schrödinger to develop the mathematical foundations of wave mechanics. Whereas in conventional quantum theory, phase waves are considered fictional, de Broglie considered them to have a certain physical reality, renaming them pilot or guiding waves – a concept developed later by Bohm in 1952.
Bohr's response in 1925 to the failure of the Bohr–Kramers–Slater theory was, as we have seen, to regard wave–particle duality as having a formal, rather than realistic, significance; he saw it as a ‘limitation of our usual means of visualization’. That same year, however, wave–particle duality was generalised by Louis-Victor de Broglie to cover the theory of matter. Moreover, the advent of quantum mechanics (i.e. matrix mechanics and wave mechanics), rather than dispelling the duality problem, heightened it. How did Bohr respond to these new developments in the quantum theory? A matter of waves In the autumn of 1923 de Broglie put forward the extremely bold hypothesis that any particle whatever is associated with a wave whose wavelength λ and frequency ν are proportional to the particle's momentum and energy respectively: λ = h / p , v = E / h . De Broglie regarded his hypothesis as the basis of a new mechanics, a wave mechanics related to classical mechanics in the same way as wave optics is related to ray optics. On this view the trajectory of a particle corresponds to the ray of the wave associated with it (i.e. the normal to the equiphase surface of the wave), and the velocity of the particle corresponds to the group velocity of the wave. De Broglie suggested, moreover, that in certain circumstances particles should exhibit diffraction effects: a stream of electrons, for example, which passes through a slit in a screen should undergo diffraction.
Arguments about particles or waves gave way to a recognized need for both particles and waves in the description of radiation. The confusion over particle versus wave properties was resolved by Louis de Broglie. He postulated that since light has a dual wave–particle nature, matter also has this nature. The idea was to perform a diffraction experiment with electrons. An interference pattern was demonstrated not only with electrons, but also with many kinds of material particles like protons and neutrons. However, any attempt to observe an interference pattern with neutral atoms was found difficult by the fact that atoms carried no charge as electrons do and could not penetrate through condensate matter like neutrons. The de Broglie wavelength of an electron in the smallest orbit turns out to be exactly equal to the circumference of the orbit predicted by Bohr. The interpretation of the interference phenomenon becomes more subtle when the light beams are replaced by individual photons or particles.
Abstract David Bohm published his “Suggested Interpretation of Quantum Theory in Terms of Hidden Variables” some twenty five years after Louis de Broglie first presented his similar Pilot Wave theory of quantum mechanics. In the following 30 years what became known as the de Broglie–Bohm approach to quantum theory was to a large extent ignored within the physics community. Even David Bohm himself became somewhat disillusioned with the lack of impact of his interpretation of quantum theory and he directed his interest elsewhere. But some 27 years after Bohm had published his interpretation of quantum theory, interest was rekindled in part by new, detailed calculations that demonstrated clearly and graphically, exactly how his interpretation explained quantum phenomena in terms of well defined individual particle trajectories. These computations encompassed two-slit interference, quantum tunnelling, neutron interferometry, Wheeler’s delayed choice experiment, orbital and intrinsic angular momentum, quantum measurement and Einstein–Podolsky–Rosen nonlocal correlations for orbital angular momentum, intrinsic angular momentum and correlated particle interferometry. Since then, the acceptance of the validity of de Broglie–Bohm theory has steadily grown, as has the interest in the consequences of the approach. For my contribution to the current celebratory volume I was asked to provide a personal review specifically of this novel work within its historical context of the last quarter of the twentieth century.
In 1923 Louis de Broglie (1892-1987) discovered the material waves and six years later received the Nobel price for this discovery. Apart these well known facts this French physicist nevertheless seems to be forgotten. Details of his life are as unknown as his efforts to describe quantum mechanics in a deterministic and objective way. Especially the actual discussion concerning the interpretation of quantum mechanics seems to justify a deeper occupation with the scientific work of Louis de Broglie. In this context the important influence of Albert Einstein is of special interest; for his photons announce the existence of material waves and it may surprise that Einstein himself did not postulate them. The basis of this short scientific biography are the publications of de Broglie (a complete bibliography is given at the end), some more or less short memories of his students and some unpublished documents found in the "Archives de l'Academie des Sciences" at Paris. The original text of the correspondence between de Broglie and Einstein is enclosed in German translation in the appendix.