Physics:Quantum mechanics/Timeline/Pre-quantum era: Difference between revisions
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{{Short description|Quantum Collection topic on Quantum mechanics/Timeline/Pre-quantum era}} | {{Short description|Quantum Collection topic on Quantum mechanics/Timeline/Pre-quantum era}} | ||
{{Quantum book backlink|Timeline}} | {{Quantum book backlink|Timeline}} | ||
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The '''pre-quantum era''' in the history of [[Physics:Quantum mechanics|quantum mechanics]] refers to the period in which | The '''pre-quantum era''' in the history of [[Physics:Quantum mechanics|quantum mechanics]] refers to the period in which classical mechanics, electromagnetism, thermodynamics, and atomic theory developed to great success, but also began to reveal deep failures at microscopic scales. These failures led directly to the [[Physics:Quantum mechanics/Timeline/Old quantum theory|old quantum theory]] and eventually to modern [[Physics:Quantum mechanics|quantum mechanics]]. | ||
The major pre-quantum problems included the nature of light, the existence of atoms and electrons, black-body radiation, atomic spectra, and the stability of atoms. The transition from classical physics to | The major pre-quantum problems included the nature of light, the existence of atoms and electrons, black-body radiation, atomic spectra, and the stability of atoms. The transition from classical physics to quantum theory began when [[Biography:Max Planck|Max Planck]] introduced energy quanta in 1900 to explain black-body radiation.<ref name="Whittaker">{{Cite book |last=Whittaker |first=Edmund T. |title=A history of the theories of aether & electricity. 2: The modern theories, 1900 - 1926 |date=1989 |publisher=Dover Publ |isbn=978-0-486-26126-3 |edition=Repr |location=New York}}</ref> | ||
, [[Biography:Albert Einstein|Albert Einstein]], [[Biography:Niels Bohr|Niels Bohr]], | , [[Biography:Albert Einstein|Albert Einstein]], [[Biography:Niels Bohr|Niels Bohr]], Louis de Broglie, [[Biography:Max Born|Max Born]], [[Biography:Paul Dirac|Paul Dirac]], [[Biography:Werner Heisenberg|Werner Heisenberg]], Wolfgang Pauli, [[Biography:Erwin Schrödinger|Erwin Schrödinger]], and Richard Feynman.]] | ||
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== Classical background == | == Classical background == | ||
Before quantum mechanics, physics was dominated by the achievements of classical mechanics and classical field theory. | Before quantum mechanics, physics was dominated by the achievements of classical mechanics and classical field theory. Isaac Newton's mechanics successfully described motion and gravitation, while later developments in thermodynamics, kinetic theory, and electromagnetism extended classical physics into heat, gases, light, electricity, and magnetism. | ||
By the end of the 19th century, many physicists believed that the foundations of physics were nearly complete. Yet several phenomena resisted classical explanation and eventually forced the introduction of discontinuity, quantization, and wave-particle duality. | By the end of the 19th century, many physicists believed that the foundations of physics were nearly complete. Yet several phenomena resisted classical explanation and eventually forced the introduction of discontinuity, quantization, and wave-particle duality. | ||
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== Wave theory of light == | == Wave theory of light == | ||
Beginning in the 17th century, Newton defended a corpuscular theory of light, treating light as made of particles. His view competed with the wave theories of | Beginning in the 17th century, Newton defended a corpuscular theory of light, treating light as made of particles. His view competed with the wave theories of Robert Hooke, Christiaan Huygens, and later Augustin-Jean Fresnel.<ref name="Whittaker" /> | ||
The wave theory gained strong support after | The wave theory gained strong support after Thomas Young demonstrated light interference in the early 19th century. Young's double-slit work showed that light could produce interference patterns, a behavior naturally explained by waves.<ref>{{cite journal|last=Young|first=Thomas|title=Bakerian Lecture: Experiments and calculations relative to physical optics|journal=Philosophical Transactions of the Royal Society|year=1804|volume=94|pages=1–16 |url=https://books.google.com/books?id=7AZGAAAAMAAJ&pg=PA1|bibcode=1804RSPT...94....1Y|doi=10.1098/rstl.1804.0001|s2cid=110408369|doi-access=free|url-access=subscription}}</ref> | ||
By the mid-19th century, the wave view dominated. | By the mid-19th century, the wave view dominated. James Clerk Maxwell then showed that light could be understood as an electromagnetic wave, unifying optics with electricity and magnetism.<ref name="Whittaker" /> | ||
== Atomic theory and kinetic theory == | == Atomic theory and kinetic theory == | ||
The atomic theory of matter gained strength through chemical work by | The atomic theory of matter gained strength through chemical work by John Dalton and Amedeo Avogadro, and through the kinetic theory of gases developed by Maxwell, Ludwig Boltzmann, and others.<ref name="Feynman-kinetic-theory">{{cite book |last1=Feynman |first1=Richard |last2=Leighton |first2=Robert |last3=Sands |first3=Matthew |title=The Feynman Lectures on Physics |volume=1 |publisher=California Institute of Technology |date=1964 |url=https://feynmanlectures.caltech.edu/I_40.html |isbn=978-0-201-50064-6 |access-date=30 September 2021}}</ref> | ||
Kinetic theory explained gases in terms of atoms and molecules in motion, but the reality of atoms remained controversial. Some physicists, including | Kinetic theory explained gases in terms of atoms and molecules in motion, but the reality of atoms remained controversial. Some physicists, including Ernst Mach, resisted atomism.<ref>{{Citation|last=Pojman|first=Paul|title=Ernst Mach|date=2020|url=https://plato.stanford.edu/archives/win2020/entries/ernst-mach/|encyclopedia=The Stanford Encyclopedia of Philosophy|editor-last=Zalta|editor-first=Edward N.|edition=Winter 2020|publisher=Metaphysics Research Lab, Stanford University|access-date=2021-09-30}}</ref> | ||
Boltzmann also suggested in 1877 that the energy levels of physical systems might be discrete, an idea that anticipated later quantum reasoning. | Boltzmann also suggested in 1877 that the energy levels of physical systems might be discrete, an idea that anticipated later quantum reasoning. | ||
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== Electrons and atomic structure == | == Electrons and atomic structure == | ||
In the late 19th century, | In the late 19th century, J. J. Thomson showed that cathode rays consisted of negatively charged particles later called [[Physics:Quantum atoms/electron|electron]]s. These particles had a mass far smaller than that of the hydrogen ion, showing that atoms contained smaller constituents.<ref name="Whittaker" /> | ||
Thomson proposed the | Thomson proposed the plum pudding model, in which electrons were embedded in a diffuse positive charge. This model was later overturned by the scattering experiments of Hans Geiger and Ernest Marsden, interpreted by Ernest Rutherford as evidence for a compact atomic nucleus.<ref name="Kragh2010">Helge Kragh (Oct. 2010). [https://css.au.dk/fileadmin/reposs/reposs-010.pdf Before Bohr: Theories of atomic structure 1850-1913]. RePoSS: Research Publications on Science Studies 10. Aarhus: Centre for Science Studies, University of Aarhus.</ref><ref name="Heilbron1968">{{Cite journal |last=Heilbron |first=John L. |date=1968 |title=The Scattering of α and β Particles and Rutherford's Atom |journal=Archive for History of Exact Sciences |volume=4 |issue=4 |pages=247–307 |doi=10.1007/BF00411591 |jstor=41133273 |issn=0003-9519}}</ref> | ||
== Radiation theory and black-body radiation == | == Radiation theory and black-body radiation == | ||
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The study of thermal radiation became one of the decisive problems that classical physics could not solve. Experiments measured the spectrum of radiation emitted by hot bodies, but no classical formula could explain the full curve. | The study of thermal radiation became one of the decisive problems that classical physics could not solve. Experiments measured the spectrum of radiation emitted by hot bodies, but no classical formula could explain the full curve. | ||
At long wavelengths, the | At long wavelengths, the Rayleigh–Jeans law worked well, but at short wavelengths it predicted an infinite emission of energy. This failure became known as the ultraviolet catastrophe. | ||
By contrast, empirical relations such as | By contrast, empirical relations such as Wien's displacement law and the Stefan–Boltzmann law described parts of the phenomenon but did not provide a complete microscopic explanation. | ||
== Planck and the first quantum idea == | == Planck and the first quantum idea == | ||
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:<math>E = h\nu</math> | :<math>E = h\nu</math> | ||
where <math>h</math> is now called the | where <math>h</math> is now called the Planck constant. Planck's law was the first quantum theory in physics, although Planck initially viewed quantization as a mathematical device rather than a fundamental property of nature.<ref name="Kragh">{{Cite web |first=Helge |last=Kragh |url=http://physicsworld.com/cws/article/print/373 |title=Max Planck: the reluctant revolutionary |publisher=PhysicsWorld.com |date=1 December 2000 |access-date=7 December 2009 |archive-date=1 April 2012 |archive-url=https://web.archive.org/web/20120401221617/http://physicsworld.com/cws/article/print/373 }}</ref> | ||
Planck received the 1918 Nobel Prize in Physics for his discovery of energy quanta.<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1918/ |title=The Nobel Prize in Physics 1918 |publisher=Nobel Foundation |access-date=2009-08-01}}</ref> | Planck received the 1918 Nobel Prize in Physics for his discovery of energy quanta.<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1918/ |title=The Nobel Prize in Physics 1918 |publisher=Nobel Foundation |access-date=2009-08-01}}</ref> | ||
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[[File:Photoelectric effect in a solid - diagram.svg|thumb|400px|right|In the photoelectric effect, light ejects electrons from a metal surface only if the frequency is high enough.]] | [[File:Photoelectric effect in a solid - diagram.svg|thumb|400px|right|In the photoelectric effect, light ejects electrons from a metal surface only if the frequency is high enough.]] | ||
In 1887, | In 1887, Heinrich Hertz observed that ultraviolet light could affect electrical discharge and cause emission from metallic surfaces.<ref name="Whittaker" /> Later, [[Biography:Philipp Lenard|Philipp Lenard]] showed that the energy of emitted electrons depended on the frequency of light, not its intensity.<ref>{{cite journal |title=Philipp Lenard and the Photoelectric Effect, 1889-1911 |first=Bruce R. |last=Wheaton |journal=Historical Studies in the Physical Sciences |volume=9 |year=1978 |pages=299–322 |doi=10.2307/27757381 |jstor=27757381}}</ref> | ||
This contradicted classical wave theory, which predicted that increasing light intensity should increase the energy of the emitted electrons. | This contradicted classical wave theory, which predicted that increasing light intensity should increase the energy of the emitted electrons. | ||
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A major pre-quantum puzzle was the existence of discrete spectral lines. When gases such as hydrogen are excited, they emit light only at specific frequencies rather than across a continuous spectrum. | A major pre-quantum puzzle was the existence of discrete spectral lines. When gases such as hydrogen are excited, they emit light only at specific frequencies rather than across a continuous spectrum. | ||
In 1885, | In 1885, Johann Balmer found a mathematical formula describing visible hydrogen spectral lines. In 1888, Johannes Rydberg generalized the formula: | ||
:<math>\frac{1}{\lambda} = R \left(\frac{1}{m^2} - \frac{1}{n^2}\right)</math> | :<math>\frac{1}{\lambda} = R \left(\frac{1}{m^2} - \frac{1}{n^2}\right)</math> | ||
where <math>R</math> is the | where <math>R</math> is the Rydberg constant.<ref name="taylor_147-8">{{cite book|last1=Taylor|first1=J. R.|last2=Zafiratos|first2=C. D.|last3=Dubson|first3=M. A.|year=2004|title=Modern Physics for Scientists and Engineers|publisher=Prentice Hall|pages=147–148|isbn=0-13-589789-0}}</ref> | ||
These formulas worked extremely well but had no classical explanation. Their use of integers strongly suggested that atomic structure involved discrete allowed states. | These formulas worked extremely well but had no classical explanation. Their use of integers strongly suggested that atomic structure involved discrete allowed states. | ||
Latest revision as of 11:34, 22 May 2026
The pre-quantum era in the history of quantum mechanics refers to the period in which classical mechanics, electromagnetism, thermodynamics, and atomic theory developed to great success, but also began to reveal deep failures at microscopic scales. These failures led directly to the old quantum theory and eventually to modern quantum mechanics.
The major pre-quantum problems included the nature of light, the existence of atoms and electrons, black-body radiation, atomic spectra, and the stability of atoms. The transition from classical physics to quantum theory began when Max Planck introduced energy quanta in 1900 to explain black-body radiation.[1] , Albert Einstein, Niels Bohr, Louis de Broglie, Max Born, Paul Dirac, Werner Heisenberg, Wolfgang Pauli, Erwin Schrödinger, and Richard Feynman.]]
Classical background
Before quantum mechanics, physics was dominated by the achievements of classical mechanics and classical field theory. Isaac Newton's mechanics successfully described motion and gravitation, while later developments in thermodynamics, kinetic theory, and electromagnetism extended classical physics into heat, gases, light, electricity, and magnetism.
By the end of the 19th century, many physicists believed that the foundations of physics were nearly complete. Yet several phenomena resisted classical explanation and eventually forced the introduction of discontinuity, quantization, and wave-particle duality.
Wave theory of light
Beginning in the 17th century, Newton defended a corpuscular theory of light, treating light as made of particles. His view competed with the wave theories of Robert Hooke, Christiaan Huygens, and later Augustin-Jean Fresnel.[1]
The wave theory gained strong support after Thomas Young demonstrated light interference in the early 19th century. Young's double-slit work showed that light could produce interference patterns, a behavior naturally explained by waves.[2]
By the mid-19th century, the wave view dominated. James Clerk Maxwell then showed that light could be understood as an electromagnetic wave, unifying optics with electricity and magnetism.[1]
Atomic theory and kinetic theory
The atomic theory of matter gained strength through chemical work by John Dalton and Amedeo Avogadro, and through the kinetic theory of gases developed by Maxwell, Ludwig Boltzmann, and others.[3]
Kinetic theory explained gases in terms of atoms and molecules in motion, but the reality of atoms remained controversial. Some physicists, including Ernst Mach, resisted atomism.[4]
Boltzmann also suggested in 1877 that the energy levels of physical systems might be discrete, an idea that anticipated later quantum reasoning.
Electrons and atomic structure
In the late 19th century, J. J. Thomson showed that cathode rays consisted of negatively charged particles later called electrons. These particles had a mass far smaller than that of the hydrogen ion, showing that atoms contained smaller constituents.[1]
Thomson proposed the plum pudding model, in which electrons were embedded in a diffuse positive charge. This model was later overturned by the scattering experiments of Hans Geiger and Ernest Marsden, interpreted by Ernest Rutherford as evidence for a compact atomic nucleus.[5][6]
Radiation theory and black-body radiation
The study of thermal radiation became one of the decisive problems that classical physics could not solve. Experiments measured the spectrum of radiation emitted by hot bodies, but no classical formula could explain the full curve.
At long wavelengths, the Rayleigh–Jeans law worked well, but at short wavelengths it predicted an infinite emission of energy. This failure became known as the ultraviolet catastrophe.
By contrast, empirical relations such as Wien's displacement law and the Stefan–Boltzmann law described parts of the phenomenon but did not provide a complete microscopic explanation.
Planck and the first quantum idea
In 1900, Max Planck proposed a model that reproduced the observed black-body spectrum. To do so, he assumed that oscillators could emit or absorb energy only in discrete units rather than continuously.[7]
The energy quantum was proportional to frequency:
where is now called the Planck constant. Planck's law was the first quantum theory in physics, although Planck initially viewed quantization as a mathematical device rather than a fundamental property of nature.[8]
Planck received the 1918 Nobel Prize in Physics for his discovery of energy quanta.[9]
Photoelectric effect
In 1887, Heinrich Hertz observed that ultraviolet light could affect electrical discharge and cause emission from metallic surfaces.[1] Later, Philipp Lenard showed that the energy of emitted electrons depended on the frequency of light, not its intensity.[10]
This contradicted classical wave theory, which predicted that increasing light intensity should increase the energy of the emitted electrons.
In 1905, Albert Einstein explained the effect by proposing that light energy is delivered in localized packets, later called photons. The energy of each light quantum is
where is frequency.[11]
Einstein's theory extended Planck's quantum idea from black-body oscillators to light itself. He later received the 1921 Nobel Prize in Physics for his work on the photoelectric effect.[12]
Atomic spectra
A major pre-quantum puzzle was the existence of discrete spectral lines. When gases such as hydrogen are excited, they emit light only at specific frequencies rather than across a continuous spectrum.
In 1885, Johann Balmer found a mathematical formula describing visible hydrogen spectral lines. In 1888, Johannes Rydberg generalized the formula:
where is the Rydberg constant.[13]
These formulas worked extremely well but had no classical explanation. Their use of integers strongly suggested that atomic structure involved discrete allowed states.
The Bohr transition
In 1913, Niels Bohr used Planck's quantum hypothesis to construct a model of the hydrogen atom. He proposed that electrons could occupy only certain allowed orbits and could emit or absorb radiation only when jumping between them.
The Bohr model explained the Rydberg formula for hydrogen by connecting spectral lines to transitions between quantized electron orbits.[14]
Although the Bohr model was later replaced by modern quantum mechanics, it marked a decisive step from the pre-quantum era to the old quantum theory.
Significance
The pre-quantum era is important because it revealed where classical physics failed. The failures were not minor technical problems but signs of a deeper structure of nature.
The key lessons were:
- Light behaves both as a wave and as localized quanta.
- Matter is composed of atoms and subatomic particles.
- Atomic spectra are discrete rather than continuous.
- Energy exchange at microscopic scales can be quantized.
- Classical mechanics and electromagnetism are incomplete at atomic scales.
These developments prepared the way for the old quantum theory and, after 1925, for modern quantum mechanics.
See also
Table of contents (217 articles)
Index
Full contents
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Whittaker, Edmund T. (1989). A history of the theories of aether & electricity. 2: The modern theories, 1900 - 1926 (Repr ed.). New York: Dover Publ. ISBN 978-0-486-26126-3.
- ↑ Young, Thomas (1804). "Bakerian Lecture: Experiments and calculations relative to physical optics". Philosophical Transactions of the Royal Society 94: 1–16. doi:10.1098/rstl.1804.0001. Bibcode: 1804RSPT...94....1Y. https://books.google.com/books?id=7AZGAAAAMAAJ&pg=PA1.
- ↑ Feynman, Richard; Leighton, Robert; Sands, Matthew (1964). The Feynman Lectures on Physics. 1. California Institute of Technology. ISBN 978-0-201-50064-6. https://feynmanlectures.caltech.edu/I_40.html. Retrieved 30 September 2021.
- ↑ Pojman, Paul (2020), Zalta, Edward N., ed., Ernst Mach (Winter 2020 ed.), Metaphysics Research Lab, Stanford University, https://plato.stanford.edu/archives/win2020/entries/ernst-mach/, retrieved 2021-09-30
- ↑ Helge Kragh (Oct. 2010). Before Bohr: Theories of atomic structure 1850-1913. RePoSS: Research Publications on Science Studies 10. Aarhus: Centre for Science Studies, University of Aarhus.
- ↑ Heilbron, John L. (1968). "The Scattering of α and β Particles and Rutherford's Atom". Archive for History of Exact Sciences 4 (4): 247–307. doi:10.1007/BF00411591. ISSN 0003-9519.
- ↑ This result was published as Planck, Max (1901). "Ueber das Gesetz der Energieverteilung im Normalspectrum". Annalen der Physik 309 (3): 553–563. doi:10.1002/andp.19013090310. Bibcode: 1901AnP...309..553P.. English translation: "On the Law of Distribution of Energy in the Normal Spectrum". http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Planck-1901/Planck-1901.html.
- ↑ Kragh, Helge (1 December 2000). "Max Planck: the reluctant revolutionary". PhysicsWorld.com. http://physicsworld.com/cws/article/print/373.
- ↑ "The Nobel Prize in Physics 1918". Nobel Foundation. http://nobelprize.org/nobel_prizes/physics/laureates/1918/.
- ↑ Wheaton, Bruce R. (1978). "Philipp Lenard and the Photoelectric Effect, 1889-1911". Historical Studies in the Physical Sciences 9: 299–322. doi:10.2307/27757381.
- ↑ Einstein, Albert (1905). "Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt". Annalen der Physik 17 (6): 132–148. doi:10.1002/andp.19053220607. Bibcode: 1905AnP...322..132E.
- ↑ "The Nobel Prize in Physics 1921". Nobel Foundation. https://www.nobelprize.org/prizes/physics/1921/summary/.
- ↑ Taylor, J. R.; Zafiratos, C. D.; Dubson, M. A. (2004). Modern Physics for Scientists and Engineers. Prentice Hall. pp. 147–148. ISBN 0-13-589789-0.
- ↑ Heilbron, John L.; Kuhn, Thomas S. (1969-01-01). "The Genesis of the Bohr Atom". Historical Studies in the Physical Sciences (University of California Press) 1: vi–290. doi:10.2307/27757291. ISSN 0073-2672.
Source attribution: Physics:Quantum mechanics/Timeline/Pre-quantum era
