In 1924 a young PhD student submitted a thesis containing the germ of an idea that would revolutionize our understanding of the material world.3 e student was Louis De Broglie4 (pronounced De Broy), and for a while he had been meditating on the wave/particle nature of light. In a moment of insight he suddenly realized that the odd behavior of light might extend to other aspects of nature as well. Perhaps particles, such as electrons, could have a wavelike nature to balance the particlelike nature of light, which had been thought of as a wave. Echoing the Planck-Einstein formulas for photons, De Broglie proposed that electrons should have a ‘pilot wave’ with frequency ( f ) and wavelength (λ) given by h mv f E h His thesis also contains an explanation for Bohr’s quantized orbits in hydrogen. If an orbiting electron had a ‘corresponding’ wave, it would have to close on itself around the circular arc of the orbit. is forces the circumference of a satisfactory orbit to be a whole number multiple of the wavelength (see Figure 18.1).
In 1924 a young PhD student submitted a thesis containing the germ of an idea that would revolutionize our understanding of the material world.3 e student was Louis De Broglie4 (pronounced De Broy), and for a while he had been meditating on the wave/particle nature of light. In a moment of insight he suddenly realized that the odd behavior of light might extend to other aspects of nature as well. Perhaps particles, such as electrons, could have a wavelike nature to balance the particlelike nature of light, which had been thought of as a wave. Echoing the Planck-Einstein formulas for photons, De Broglie proposed that electrons should have a ‘pilot wave’ with frequency ( f ) and wavelength (λ) given by h mv f E h His thesis also contains an explanation for Bohr’s quantized orbits in hydrogen. If an orbiting electron had a ‘corresponding’ wave, it would have to close on itself around the circular arc of the orbit. is forces the circumference of a satisfactory orbit to be a whole number multiple of the wavelength (see Figure 18.1).
In 1924, a young PhD student submitted a thesis containing the germ of an idea that would revolutionize our understanding of the material world. The student was Louis De Broglie, and for a while, he had been meditating on the wave/particle nature of light. De Broglie’s ideas were greeted rather sceptically at first. His PhD supervisor even asked for a second copy so he could send it to Einstein for his opinion. Einstein gave the work his seal of approval. News of De Broglie’s thesis spread around the physics community from 1924 to 1925. In autumn 1925, Erwin Schrodinger was visiting colleagues in Switzerland and was asked to present a summary of De Broglie’s work. Having studied De Broglie’s thesis in some detail he became an enthusiastic supporter. During the Christmas and New Year of 1925/1926, Schrodinger holidayed in the Alps with his mistress. On his return, he had a functioning wave equation worked out.
Where did we get that [equation] from? Nowhere. It is not possible to derive it from anything you know. It came out of the mind of Schrödinger. Richard Feynman De Broglie's matter waves The early struggles of physicists towards a quantum theory were mostly concerned with attempts to understand the nature of light. The traditional picture of light as a wave motion had been challenged by Planck and Einstein. They had shown that certain experimental results that were impossible to understand in terms of a wave picture could be easily explained if light was thought of as a stream of particles, now called photons. William Bragg, who, with his son, won the 1915 Nobel Prize for studies of crystal structure using X-rays, summarized this dilemma for physics by exclaiming in despair that he was teaching the corpuscular theory of light on Mondays, Wednesdays and Fridays, and the undulatory theory on Tuesdays, Thursdays and Saturdays! Physicists were still wrestling with these apparently contradictory properties of light when, in 1924, Prince Louis de Broglie (pronounced ‘de Broy’) suggested that all matter, even objects that we usually think of as particles – such as electrons – should also display wavelike behaviour! This revolutionary idea was completely unexpected and, what is more, was included by de Broglie in his Ph. D. thesis. Like most people, physicists are generally reluctant to accept any wild new idea, especially if there is not a shred of evidence to support it.
Abstract The particle-wave duality was perhaps the most startling outcome of the conceptual revolution that swept through physics during the first three decades of the twentieth century. That photons—the packets, or quanta, of light— behaved in some respects as particles, in others as waves, had already been noted when the due (later Prince) Louis de Broglie conjectured that the same might be true of other particles, such as electrons. Sitting in an eyrie in the Eiffel Tower as a meteorological observer during the First World War, de Broglie had time to ruminate on these matters and to develop an equation relating the momentum of the particle to its wavelength. This formed the substance of his doctoral dissertation, which he submitted to the University of Paris in 1924 and which earned him the Nobel Prize five years later.
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.
Toward the end of the nineteenth century, it became clear that some experiments cannot be explained on the basis of known physics, now referred to as classical physics. In 1900, Max Planck was able to correctly describe the distribution of blackbody radiation energy as a function of wavelength λ or frequency ν = c/λ. He had to accept the existence of energy packets (quanta) with energy E = hν. A few years later, Albert Einstein found that this unexpected relation between energy and frequency is also necessary in order to understand photoemission from metallic surfaces. A decade later, Niels Bohr arrived at the correct equation for the electronic spectrum of the hydrogen atom by applying “quantum conditions” on the motion of the electron around the nucleus and the Planck’s relation E = hν on the energy difference between the energy levels (1916). A decade later, Heisenberg, Born, and Jordan introduced “quantum mechanics” and de Broglie and Schrödinger (1925-1926) introduced “wave mechanics.”
On 13 March 1926, the first of six papers on wave mechanics by Erwin Schrödinger was published in the Annalen der Physik with the title Quantisation as an eigenvalue problem (Part 1) (Schrödinger, 1926b). The startling first paragraph reads: ‘In this paper, I wish to consider, first, the simple case of the hydrogen atom (nonrelativistic and unperturbed), and show that the customary quantum conditions can be replaced by another postulate, in which the concept of “whole numbers”, merely as such, is not introduced. Rather, when integralness does appear, it arises in the same natural way as it does in the case of node-numbers of a vibrating string. The new conception is capable of generalisation, and strikes, I believe, very deeply at the true nature of quantum rules.’ These papers were the fruits of an extraordinary burst of creativity on Schrödinger's part which resulted from his interactions with Einstein in the latter part of 1925. Central to these exchanges were de Broglie's remarkable researches which culminated in his famous PhD dissertation and published papers of 1924. These events have already be recounted in Chap. 9. The subsequent developments which led to Schrödinger's discovery of the equation which bears his name will be taken up in Sect. 14.2, but let us first understand more about Schrödinger's background. Schrödinger's background in physics and mathematics Education and career up to 1925 Unlike Heisenberg, Jordan, Pauli and Dirac, Erwin Schrödinger was not one of the young Turks who developed Knabenphysik , young man's physics.