“In this derivation Bohr had relied on the old idea of classical radiation theory, that the frequencies of spectral lines should agree with the frequency of the electron’s orbital motion, but he had assumed this only for the largest orbits, with large n. The light frequencies he calculated for transitions between lower states, such as n=2 → n=1, did not at all agree with the orbital frequency of the initial or final state. So Bohr’s work represented another large step away from classical physics.”

—  Steven Weinberg

Source: Lectures on Quantum Mechanics (2012, 2nd ed. 2015), Ch. 1: Historical Introduction

Adopted from Wikiquote. Last update Sept. 27, 2023. History

Help us to complete the source, original and additional information

Do you have more details about the quote "In this derivation Bohr had relied on the old idea of classical radiation theory, that the frequencies of spectral line…" by Steven Weinberg?
Steven Weinberg photo
Steven Weinberg46
American theoretical physicist 1933

Related quotes

James Jeans photo

“Bohr had… discovered that the frequencies corresponding to very large integers could be calculated accurately from the classical mechanics; they were simply the number of times that an ordinary electron would complete the circuit of its orbit in one second when it was at a very great distance from the nucleus of the atom to which it belonged. This could only mean that when an electron receded to a great distance from the nucleus of its atom, it not only assumed the properties of an ordinary electron, but also behaved as directed by the classical mechanics. Yet the classical mechanics failed completely for the calculation of frequencies corresponding to small orbits.”

James Jeans (1877–1946) British mathematician and astronomer

Physics and Philosophy (1942)

James Jeans photo

“This spectrum is of the type known in spectroscopy as a line-spectrum. Its appearance is that of a group of bright lines on a dark background, indicating that the radiation divides itself between a number of clearly defined frequencies, and that there is no radiation in between. Before Bohr's explanation appeared, these frequencies had been supposed to belong to some sort of vibration taking place in the hydrogen atom - like frequencies of the musical note which is heard when a bell or piano wire is made to vibrate. It now became clear that they had an entirely different origin. The energy exhibited in the spectrum was not liberated by a vibration, or any kind of continuous motion, but by the sudden jump of an electron to an orbit of lower energy, and its frequency was determined by the compulsion put upon it to form a single quantum.”

James Jeans (1877–1946) British mathematician and astronomer

Physics and Philosophy (1942)

James Jeans photo

“In every previous application of the quantum law, Planck's law, that the energy is h [Planck's constant] times the frequency, had been used to deduce the energy of a quantum when the frequency of the radiation was already known. In the present case the formula was used the other way; the energy of the emitted photon was known to begin with, and the formula was utilized to deduce its frequency. The frequencies calculated in this way are found to agree completely and exactly with those of the spectrum of hydrogen.”

James Jeans (1877–1946) British mathematician and astronomer

Physics and Philosophy (1942)

“After a large earthquake the earth "rings" like a bell; this motion can be observed on sensitive instruments up to a month after a large event. These oscillations have specific frequencies which are properties of the whole earth and which can be measured very accurately indeed. The lowest frequency oscillation has a period of about one hour. Any combination of seismic waves can be represented as an equivalent combination of normal modes. In practice the mode representation is most useful at low frequency — for seismic waves above about 40 s — since at higher frequencies the number of modes becomes prohibitively large.”

David Gubbins (1947) British university teacher

[Seismology and plate tectonics, 1990, http://books.google.com/books?id=tZRxPzwoChIC&pg=PA5] (p. 5)
Seismology and Plate Tectonics (1990)

James Jeans photo

“In 1925 Heisenberg made a new attempt, on entirely novel lines, to obtain an explanation of atomic spectra. Working in collaboration with Bohr, he had come to the conclusion that the imperfections of Bohr's theory had been a consequence of assuming too simple a model for the atom. For Bohr had not only assumed that the atom consisted of particles moving through space and time, but also that the particles inside atoms were of the same kind as the electrons outside atoms.”

James Jeans (1877–1946) British mathematician and astronomer

Physics and Philosophy (1942)

Richard von Mises photo

“Apart from this older generation, there is scarcely a modern mathematician who still adheres without reservation to the classical theory of probability. The majority have more or less accepted the frequency definition.”

Richard von Mises (1883–1953) Austrian physicist and mathematician

Third Lecture, Critical Discussion of the Foundations of Probability, p. 81
Probability, Statistics And Truth - Second Revised English Edition - (1957)

Ralph Ellison photo

“Who knows but that, on the lower frequencies, I speak for you?”

Ralph Ellison book Invisible Man

Epilogue (last line of the novel).
Source: Invisible Man (1952)

“Everything has a frequency. And whatever you’re feeling is bringing everything into your life that’s on a similar frequency to you.”

Ralph Smart

Johannes Kepler photo

“I was almost driven to madness in considering and calculating this matter. I could not find out why the planet would rather go on an elliptical orbit. Oh, ridiculous me! As the liberation in the diameter could not also be the way to the ellipse. So this notion brought me up short, that the ellipse exists because of the liberation. With reasoning derived from physical principles, agreeing with experience, there is no figure left for the orbit of the planet but a perfect ellipse.”

Johannes Kepler book Mysterium Cosmographicum

As translated and quoted in John Freely, Before Galileo: The Birth of Modern Science in Medieval Europe (2012), in chapter 58, at an unspecified page.
Mysterium Cosmographicum (1596), Astronomia nova (1609)

“Quantum mechanics explains the physical stability of the atom by predicting its allowed discrete energy levels and defining the wave functions (also called atomic orbitals) associated with each energy level. The orbitals determine the probability density for finding the electrons at particular locations in the atom when the electrons are in a specific quantum state.”

David W. Oxtoby (1951) President of Pomona college

Principles of Modern Chemistry (7th ed., 2012), Ch. 5 : Quantum Mechanics and Atomic Structure

Related topics