In the year 1900 Max Planck was led by experimental observations to propose a strange formula for the intensity as a function of frequency for light emitted by a cavity. It relied on peculiar properties to be obeyed by the emitters and absorbers in the cavity. I highlight the mathematically suggestive nature of the formula, accessible even to a high school student, that could have provided a clue to the physical reasoning of Planck. In 1905, Einstein made the bold photon hypothesis and was able to predict the formula for the photoelectric effect which was not fully explored then. The first part of this article concerns the period 1905 to 1923 with a possible explanation for the difficulties in acceptance of the new concept. In the second part of the article I present how S. N. Bose's 1924 paper provided a systematic derivation of Planck formula by consistently adopting the conception of photons within Boltzmann's framework. In conclusion we discuss the implications of Quantum Mechanics that eventually emerged, showing that the seeds of some of its uncanny conceptual content were already foreshadowed in Einstein's proposal.
In the year 1900 Max Planck was led by experimental observations to propose a strange formula for the intensity as a function of frequency for light emitted by a cavity. It relied on peculiar properties to be obeyed by the emitters and absorbers in the cavity. I highlight the mathematically suggestive nature of the formula, accessible even to a high school student, that could have provided a clue to the physical reasoning of Planck. In 1905, Einstein made the bold photon hypothesis and was able to predict the formula for the photoelectric effect which was not fully explored then. The first part of this article concerns the period 1905 to 1923 with a possible explanation for the difficulties in acceptance of the new concept. In the second part of the article I present how S. N. Bose's 1924 paper provided a systematic derivation of Planck formula by consistently adopting the conception of photons within Boltzmann's framework. In conclusion we discuss the implications of Quantum Mechanics that eventually emerged, showing that the seeds of some of its uncanny conceptual content were already foreshadowed in Einstein's proposal.
Startling findings concerning the Planck‟s quantum equation, E = hv, have been brought to light in this work. It has been conclusively proven that the conceptual correctness of this quantum equation cannot be justified by any physical reasoning, and that there have emerged a newly formulated but promising quantum equation, P = bv, which relates the power „P‟ of a quantum oscillator, such as a photon, with its frequency „v‟ (where ‘b’is the elementary quantum of energy observable in nature), to be the right kind of quantum equation. Since the core concept in the Einstein‟s theory of the photoelectric effect is critically dependent on the correctness of the Planck‟s quantum equation, bringing about an appropriate modification in the Einstein‟s derivation of the photoelectric effect has been deemed essential. Reformulation of the Einstein‟s photoelectric equation has been carried out in this work taking into consideration the newly emerged quantum perspective as well as the concept of energy-power dichotomy that photons and photoelectrons do exhibit. Thus, the Einstein‟s photoelectric equation expressed in all energy terms, Ee = hv h v0, is get converted into all power terms, Pe = bv bv0. This modified form of the Einstein‟s photoelectric equation has been found to be capable of providing satisfactory explanation to all the salient features the photoelectric effect exhibits.
Abstract With the failure of classical physics to explain the experimentally observed black body radiation spectrum, the photoelectric effect and the existence of narrow spectral lines in the light emitted by excited atoms, physicists were forced to reach out for new ideas. Following Planck’s initial “drastic hypothesis” of light “quanta”, Einstein led the way in exploring some of the myriad implications of this idea. In particular, the study of fluctuations led to a new understanding of the interaction of electromagnetic radiation with atoms. Einstein invented the photon by showing, through fluctuation studies, that light emitted by atoms must be in the form of plane waves. These ideas led to the first notions regarding the quantization of matter and its dynamics.
This chapter presents the basic physical ideas that underpin the quantum theory. Historians place the beginnings of the quantum theory at 1900. That year Max Planck published his famous formula for the distribution of energy as a function of frequency in black-body radiation. Curiously, although radiation theory gave birth to quantum mechanics, the interaction of matter and electromagnetic radiation is a rather advanced topic in quantum mechanics and it took almost fifty years for an acceptable formulation to be achieved. One reason for this is that photons are quanta of the electromagnetic field, and the quantum theory of fields requires a relativistic treatment to be entirely successful. The corpuscular nature of light was only half of the input that gave birth to quantum mechanics. The other half concerns matter. Given that the discreteness of photons manifests itself during the emission and absorption process, it is not surprising to find that quantum oddities afflict the behaviour of material particles too.
Planck’s 1900 introduction of the “energy elements”, i.e., electromagnetic radiation quanta of energy hν each, for founding his radiation law marks the origin of quantum theory and is discussed in all courses on this subject. Surprisingly, the question whether Planck really implied quantisation is debated among historians of physics. We present a simplified account of that debate which also sheds light on the issue of indistinguishability and Einstein’s light quantum hypothesis. Here, the relevance of the notion ‘(in)distinguishability’ is often overemphasized. It has to be treated together with ‘equality’, ‘identity’, and ‘interchangeability’, where the latter one is the decisive notion in this context. As a result, the difference between Planck’s and Einstein’s concepts of ‘light particles’ becomes more easily to grasp. For that and many other reasons, we believe that the teaching of quantum physics benefits from including the material presented here, and that beyond the demand of historical completeness. Nevertheless, for the sake of our readers’ convenience, we almost completely reprint Planck’s former students Hettner’s remembering of Planck’s way to his radiation law, together with its translation into English. It seems that Planck has not really done the calculations described in his December 1900 lecture. For this, following Becker, we show how to overcome the difficulties over there, and we sketch his simplifying approach in his subsequent 1901 article. Strangely enough, in his 1906/07 lectures on the theory of heat radiation, Planck deviates from those calculations and obtains a non-extensive entropy. This, too, is most easily analyzed using Bach’s three-level scheme ‘configuration. occupation. occupancy’ for the counting combinatorics involved. Boltzmann’s 1877, Planck’s 1900, Einstein’s 1905, Bose’s 1924, and other treatments are systematized using that scheme
In this chapter, three problems whose resolution laid the foundation of quantum mechanics are discussed. First the pioneering work of Max Planck is described who explained the spectrum of light emitted from a so-called blackbody by making a bold ansatz that the energy associated with the oscillations of electrons comes in packets or quanta of energy. Second it is shown how Einstein invoked Planck’s hypothesis to explain the photoelectric effect by arguing that light should come in packets or quanta of energy and this energy should be proportional to the frequency. Electrons are emitted if the energy of the quantum of light, which has come to be known as a photon, is higher than a critical value. The third problem relates to the atomic structure of hydrogen. A full description is given of how Bohr applied a quantization condition to explain the emission of light at certain specific frequencies.
Classical electromagnetics in free space leaves no room for accommodation of a light particle. To underline this, it is sufficient to remember that Einstein in order to reach his lightquantum (energy-quantum) hypothesis had to mix classical theoretical physics with a piece of experimental information that defies description in classical terms. In his 1905-paper Einstein concluded [60]:Monochromatic radiation of low density (within the range of validity of Wien’s radiation formula) behaves thermodynamically as though it consisted of a number of mutually independent energy quanta of magnitude hν. The introduction of light quanta in the Wien regime (the high-frequency part of the Planck blackbody radiation law) is the first step toward the concept of electromagnetic radiation as a Bose gas of photons [180, 39, 68, 69]. Although a photon gas obeys Bose-Einstein statistics for all frequencies the statistical independence assumed by Einstein in 1905 is not true in general. Einstein used Boltzmann statistics when he conjectured the existence of light quanta. In the Wien regime Boltzmann and Bose-Einstein statistics lead to the same conclusion since the mean number of particles (photons) with a given energy is much less than one. The circumstance that the light quanta are not statistically independent in Bose-Einstein counting finds its explanation in quantum mechanics. Hence, the statistical correlation is induced by the requirement of totally symmetric wave functions.