Quantum Mechanics Explained: From the Strange to the Fascinating
Physics of atoms, electrons, and the very small
Quantum mechanics describes the behavior of matter and energy at the smallest scales — and it is deeply, profoundly strange. Particles can be in two states at once (superposition). Two particles can be correlated across any distance in ways that seem to defy local physics (entanglement). Light behaves as both a wave and a particle depending on how you observe it. These are not philosophical claims — they are experimentally confirmed facts that have reshaped our understanding of reality at its most fundamental level.
Physics: Wolfgang Pauli
Wolfgang Pauli (1900) Wolfgang Ernst Pauli ( PAW-lee; German: [ˈpaʊ̯li] ; 25 April 1900 – 15 December 1958) was an Austrian–Swiss theoretical physicist and a pioneer of quantum mechanics.
Read commentary →Physics: Stern–Gerlach experiment
Stern–Gerlach experiment By: Stern and Gerlach (1922) In quantum physics, the Stern–Gerlach experiment demonstrated that the spatial orientation of angular momentum is quantized.
Read commentary →Physics: Arnold Sommerfeld
Arnold Sommerfeld (1868) Arnold Johannes Wilhelm Sommerfeld (German: [ˈaʁnɔlt ˈzɔmɐˌfɛlt]; 5 December 1868 – 26 April 1951) was a German theoretical physicist who pioneered developments in both atomic and quantum physics, and also educated and mentored many students for the new era of theoretical physics.
Read commentary →Physics: Niels Bohr
Niels Bohr (1885) Niels Henrik David Bohr (; Danish: [ˈne̝ls ˈpoɐ̯ˀ]; 7 October 1885 – 18 November 1962) was a Danish theoretical physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922.
Read commentary →Physics: Uncertainty principle
Uncertainty principle Form: ΔxΔp ≥ h/4π The uncertainty principle, also known as Heisenberg's indeterminacy principle, is a fundamental concept in quantum mechanics.
Read commentary →Physics: Max Planck
Max Planck (1858) Max Karl Ernst Ludwig Planck (; German: [ˈmaks ˈplaŋk] ; 23 April 1858 – 4 October 1947) was a German theoretical physicist.
Read commentary →Physics: QED renormalization established
1948: QED renormalization established In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics.
Read commentary →Physics: Klaus von Klitzing
Klaus von Klitzing (1943) Klaus von Klitzing (German: [ˈklaʊs fɔn ˈklɪtsɪŋ] ; born 28 June 1943) is a German physicist, known for discovery of the integer quantum Hall effect, for which he was awarded the 1985 Nobel Prize in Physics.
Read commentary →Physics: Anton Zeilinger
Anton Zeilinger (1945) Anton Zeilinger (German: [ˈanton ˈtsaɪlɪŋɐ]; born 20 May 1945) is an Austrian quantum physicist and Nobel laureate in physics of 2022.
Read commentary →Physics: 2012 Nobel Prize in Physics
2012 Nobel Prize in Physics Awarded to: Serge Haroche, David J. Wineland Ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems.
Read commentary →Physics: Born rule
Born rule The Born rule is a postulate of quantum mechanics that gives the probability that a measurement of a quantum system will yield a given result.
Read commentary →Physics: Planck introduces quantum hypothesis
1900: Planck introduces quantum hypothesis The Planck constant, or Planck's constant, denoted by h {\displaystyle h} , is a fundamental physical constant of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and a particle's momentum is equal to the wavenumber of the associated mat
Read commentary →Physics: Louis de Broglie
Louis de Broglie (1892) Louis Victor Pierre Raymond, 7th Duc de Broglie (French: [də bʁɔj] ; 15 August 1892 – 19 March 1987) was a French theoretical physicist and aristocrat known for his contributions to quantum theory.
Read commentary →Physics: Alain Aspect
Alain Aspect (1947) Alain Jean Aspect (French: [aspɛ] ; born 15 June 1947) is a French physicist noted for his experimental work on quantum entanglement.
Read commentary →Physics: Compton scattering
Compton scattering Compton scattering (or the Compton effect) is the quantum theory of scattering of a high-frequency photon through an interaction with a charged particle, usually an electron.
Read commentary →Physics: Quantum tunnelling
Quantum tunnelling In physics, quantum tunnelling, barrier penetration, or simply tunnelling is a quantum mechanical phenomenon in which an object such as an electron or atom passes through a potential energy barrier that, according to classical mechanics, should not be passable due to the object not having sufficient energy to pass or surmount the barrier.
Read commentary →Physics: Kinematic equation
Kinematic equation Form: s = ut + ½at² In physics, classical mechanics is a theory that describes the effect of forces on the motion of macroscopic objects and bulk matter, without considering quantum effects, and often without incorporating relativistic effects either.
Read commentary →Physics: Planck constant
Planck constant h = 6.626×10⁻³⁴ J·s The Planck constant, or Planck's constant, denoted by h {\displaystyle h} , is a fundamental physical constant of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and a particle's momentum is equal to the wavenumber of the associated matter wav
Read commentary →Physics: Schrodinger formulates wave equation
1926: Schrodinger formulates wave equation The Schrödinger equation is a partial differential equation that governs the wave function of a non-relativistic quantum-mechanical system.
Read commentary →Physics: Planck time
Planck time tp = 5.391×10⁻⁴⁴ s In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB.
Read commentary →Physics: Complementarity (physics)
Complementarity (physics) In physics, complementarity is a conceptual aspect of quantum mechanics that Niels Bohr regarded as an essential feature of the theory.
Read commentary →Physics: Planck temperature
Planck temperature Tp = 1.417×10³² K In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB.
Read commentary →Physics: Heisenberg develops matrix mechanics
1925: Heisenberg develops matrix mechanics Matrix mechanics is a formulation of quantum mechanics created by Werner Heisenberg, Max Born, and Pascual Jordan in 1925.
Read commentary →Physics: Quantum entanglement
Quantum entanglement Quantum entanglement is the phenomenon wherein the quantum state of each particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance.
Read commentary →Physics: Freeman Dyson
Freeman Dyson (1923) Freeman John Dyson (15 December 1923 – 28 February 2020) was a British-American theoretical physicist and mathematician known for his works in quantum field theory, astrophysics, random matrices, mathematical formulation of quantum mechanics, condensed matter physics, nuclear physics, and engineering.
Read commentary →Physics: Enrico Fermi
Enrico Fermi (1901) Enrico Fermi (Italian: [enˈriːko ˈfermi]; 29 September 1901 – 28 November 1954) was an Italian–American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project.
Read commentary →Physics: Electrostatics
Electrostatics Electrostatics is a branch of physics that studies slow-moving or stationary electric charges on macroscopic objects where quantum effects can be neglected.
Read commentary →Physics: Wave–particle duality
Wave–particle duality Wave–particle duality is the concept in quantum mechanics that fundamental entities of the universe, like photons and electrons, exhibit particle or wave properties according to the experimental circumstances.
Read commentary →Physics: 2025 Nobel Prize in Physics
2025 Nobel Prize in Physics Awarded to: John Clarke, Michel H. Devoret, John M. Martinis The discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.
Read commentary →Physics: Arthur Compton
Arthur Compton (1892) Arthur Holly Compton (September 10, 1892 – March 15, 1962) was an American physicist who shared the 1927 Nobel Prize in Physics with C.
Read commentary →Physics: Higgs boson discovered
2012: Higgs boson discovered The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory.
Read commentary →Physics: 1965 Nobel Prize in Physics
1965 Nobel Prize in Physics Awarded to: Sin-Itiro Tomonaga, Julian Schwinger, Richard P. Feynman Their fundamental work in quantum electrodynamics, with deep-ploughing consequences for the physics of elementary particles.
Read commentary →Physics: 2001 Nobel Prize in Physics
2001 Nobel Prize in Physics Awarded to: Eric A. Cornell, Wolfgang Ketterle, Carl E. Wieman The achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates.
Read commentary →Physics: 1964 Nobel Prize in Physics
1964 Nobel Prize in Physics Awarded to: Charles Hard Townes, Nicolay Gennadiyevich Basov, Aleksandr Mikhailovich Prokhorov Fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle.
Read commentary →Physics: Compton wavelength
Compton wavelength λc = 2.426×10⁻¹² m Compton scattering (or the Compton effect) is the quantum theory of scattering of a high-frequency photon through an interaction with a charged particle, usually an electron.
Read commentary →Physics: De Broglie hypothesis
De Broglie hypothesis Matter waves are a central part of the theory of quantum mechanics, being half of wave–particle duality.
Read commentary →Physics: Max Born
Max Born (1882) Max Born (German: [ˈmaks ˈbɔʁn] ; 11 December 1882 – 5 January 1970) was a German–British theoretical physicist who was instrumental in the development of quantum mechanics.
Read commentary →Physics: de Broglie proposes matter waves
1924: de Broglie proposes matter waves Matter waves are a central part of the theory of quantum mechanics, being half of wave–particle duality.
Read commentary →Physics: Hans Bethe
Hans Bethe (1906) Hans Albrecht Eduard Bethe (; German: [ˈhans ˈbeːtə] ; July 2, 1906 – March 6, 2005) was a German-American physicist who made major contributions to nuclear physics, astrophysics, quantum electrodynamics and solid-state physics, and received the Nobel Prize in Physics in 1967 for his work on the theory of stellar nucleosynthesis.
Read commentary →Physics: John Clauser
John Clauser (1942) John Francis Clauser (; born December 1, 1942) is an American theoretical and experimental physicist known for contributions to the foundations of quantum mechanics, in particular the Clauser–Horne–Shimony–Holt inequality.
Read commentary →Physics: Fermi's golden rule
Fermi's golden rule In quantum physics, Fermi's golden rule is a formula that describes the transition rate (the probability of a transition per unit time) from one energy eigenstate of a quantum system to a group of energy eigenstates in a continuum, as a result of a weak perturbation.
Read commentary →Physics: Magnetic flux quantum
Magnetic flux quantum Φ₀ = 2.068×10⁻¹⁵ Wb Quantum mechanics is the fundamental physical theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms.
Read commentary →Physics: Planck mass
Planck mass Mp = 2.176×10⁻⁸ kg In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB.
Read commentary →Physics: Superposition principle
Superposition principle The superposition principle, also known as superposition property, states that, for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually.
Read commentary →Physics: Werner Heisenberg
Werner Heisenberg (1901) Werner Karl Heisenberg (; German: [ˈvɛʁnɐ ˈhaɪzn̩bɛʁk] ; 5 December 1901 – 1 February 1976) was a German theoretical physicist, one of the main pioneers of the theory of quantum mechanics and a principal scientist in the German nuclear program during World War II.
Read commentary →Physics: Ferenc Krausz
Ferenc Krausz (1962) Ferenc Krausz (born 17 May 1962) is a Hungarian physicist working in attosecond science.
Read commentary →Physics: Higgs boson
Higgs boson The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory.
Read commentary →Physics: Erwin Schrodinger
Erwin Schrodinger (1887) Erwin Rudolf Josef Alexander Schrödinger (12 August 1887 – 4 January 1961) was an Austrian–Irish theoretical physicist who developed fundamental results in quantum theory.
Read commentary →Physics: Edward Witten
Edward Witten (1951) Edward Witten (born August 26, 1951) is an American theoretical physicist known for his contributions to string theory, topological quantum field theory, and various areas of mathematics.
Read commentary →Physics: Photon
Photon A photon (from Ancient Greek φῶς, φωτός (phôs, phōtós) 'light') is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force.
Read commentary →Physics: Bohr model
Bohr model In atomic physics, the Bohr model or Rutherford–Bohr model is an obsolete model of the atom that incorporated some early quantum concepts.
Read commentary →Physics: Satyendra Nath Bose
Satyendra Nath Bose (1894) Satyendra Nath Bose (; 1 January 1894 – 4 February 1974) was an Indian theoretical physicist and mathematician.
Read commentary →Physics: Paul Dirac
Paul Dirac (1902) Paul Adrien Maurice Dirac ( dih-RAK; 8 August 1902 – 20 October 1984) was a British theoretical physicist who is considered to be one of the founders of quantum mechanics.
Read commentary →Physics: Francis Crick
Francis Crick (1916) Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist.
Read commentary →Physics: Photoelectric effect
Photoelectric effect The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light.
Read commentary →Physics: Pauli exclusion principle
Pauli exclusion principle In quantum mechanics, the Pauli exclusion principle (German: Pauli-Ausschlussprinzip) states that two or more identical particles with half-integer spins (i.
Read commentary →Physics: Franck–Hertz experiment
Franck–Hertz experiment By: Franck and Hertz (1914) The Franck–Hertz experiment was the first electrical measurement to clearly show the quantum nature of atoms.
Read commentary →Physics: Kinematic equation
Kinematic equation Form: v² = u² + 2as In physics, classical mechanics is a theory that describes the effect of forces on the motion of macroscopic objects and bulk matter, without considering quantum effects, and often without incorporating relativistic effects either.
Read commentary →Physics: Bose–Einstein condensate
Bose–Einstein condensate In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero, i.
Read commentary →Physics: Albert Einstein
Albert Einstein (1879) Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist best known for developing the theory of relativity.
Read commentary →Physics: 1932 Nobel Prize in Physics
1932 Nobel Prize in Physics Awarded to: Werner Karl Heisenberg The creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen.
Read commentary →Physics: Reduced Planck constant
Reduced Planck constant ℏ = 1.055×10⁻³⁴ J·s The Planck constant, or Planck's constant, denoted by h {\displaystyle h} , is a fundamental physical constant of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and a particle's momentum is equal to the wavenumber of the associated ma
Read commentary →Physics: Planck-Einstein relation
Planck-Einstein relation Form: E = hf The Planck constant, or Planck's constant, denoted by h {\displaystyle h} , is a fundamental physical constant of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and a particle's momentum is equal to the wavenumber of the associated matter w
Read commentary →Physics: 1921 Nobel Prize in Physics
1921 Nobel Prize in Physics Awarded to: Albert Einstein His services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.
Read commentary →Physics: Bohr radius
Bohr radius aB = 5.292×10⁻¹¹ m In atomic physics, the Bohr model or Rutherford–Bohr model is an obsolete model of the atom that incorporated some early quantum concepts.
Read commentary →Physics: Tau mass
Tau mass mτ = 3.167×10⁻²⁷ kg The tau (τ), also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of 1/2.
Read commentary →Physics: Conductance quantum
Conductance quantum G₀ = 7.748×10⁻⁵ S The quantum Hall effect (or integer quantum Hall effect) is a quantized version of the Hall effect which is observed in two-dimensional electron systems subjected to low temperatures and strong magnetic fields, in which the Hall resistance Rxy exhibits steps that take on the quantized values R x
Read commentary →Physics: Photoelectric effect
Photoelectric effect The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light.
Read commentary →Physics: Einstein explains photoelectric effect
1905: Einstein explains photoelectric effect The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light.
Read commentary →Physics: 1954 Nobel Prize in Physics
1954 Nobel Prize in Physics Awarded to: Max Born, Walther Bothe His fundamental research in quantum mechanics, especially for his statistical interpretation of the wavefunction / for the coincidence method and his discoveries made therewith.
Read commentary →Physics: Nuclear fission
Nuclear fission Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei.
Read commentary →Physics: Bell's theorem
Bell's theorem Bell's theorem is a term encompassing a number of closely related results in physics, all of which determine that quantum mechanics is incompatible with local hidden-variable theories, given some basic assumptions about the nature of measurement.
Read commentary →Physics: Planck length
Planck length lp = 1.616×10⁻³⁵ m In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB.
Read commentary →Physics: Bohr model energy levels
Bohr model energy levels Form: E = -13.6/n² eV In atomic physics, the Bohr model or Rutherford–Bohr model is an obsolete model of the atom that incorporated some early quantum concepts.
Read commentary →Physics: Reinhard Genzel
Reinhard Genzel (1952) Reinhard Genzel (German pronunciation: [ˈʁaɪnhaʁt ˈɡɛntsl̩] ; born 24 March 1952) is a German astrophysicist, co-director of the Max Planck Institute for Extraterrestrial Physics, a professor at LMU and an emeritus professor at the University of California, Berkeley.
Read commentary →Physics: Entropy
Entropy Entropy is a scientific concept, most commonly associated with states of disorder, randomness, or uncertainty.
Read commentary →Physics: Aspect's experiment
Aspect's experiment By: Alain Aspect (1982) Aspect's experiment was the first quantum mechanics experiment to demonstrate the violation of Bell's inequalities with photons using distant detectors.
Read commentary →Physics: Bohr model explains atomic spectra
1913: Bohr model explains atomic spectra In atomic physics, the Bohr model or Rutherford–Bohr model is an obsolete model of the atom that incorporated some early quantum concepts.
Read commentary →Physics: Uncertainty principle
Uncertainty principle The uncertainty principle, also known as Heisenberg's indeterminacy principle, is a fundamental concept in quantum mechanics.
Read commentary →Physics: Muon mass
Muon mass mμ = 1.883×10⁻²⁸ kg A muon ( M(Y)OO-on; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2 ħ, but with a much greater mass.
Read commentary →Physics: 1998 Nobel Prize in Physics
1998 Nobel Prize in Physics Awarded to: Robert B. Laughlin, Horst L. Störmer, Daniel C. Tsui Their discovery of a new form of quantum fluid with fractionally charged excitations.
Read commentary →Physics: 1999 Nobel Prize in Physics
1999 Nobel Prize in Physics Awarded to: Gerardus 't Hooft, Martinus J.G. Veltman Elucidating the quantum structure of electroweak interactions in physics.
Read commentary →Physics: Nuclear fission discovered
1938: Nuclear fission discovered Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei.
Read commentary →Physics: 2005 Nobel Prize in Physics
2005 Nobel Prize in Physics Awarded to: Roy J. Glauber, John L. Hall, Theodor W. Hänsch His contribution to the quantum theory of optical coherence / for their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique.
Read commentary →Physics: 1945 Nobel Prize in Physics
1945 Nobel Prize in Physics Awarded to: Wolfgang Pauli The discovery of the Exclusion Principle, also called the Pauli Principle.
Read commentary →Physics: Kinematic equation
Kinematic equation Form: v = u + at In physics, classical mechanics is a theory that describes the effect of forces on the motion of macroscopic objects and bulk matter, without considering quantum effects, and often without incorporating relativistic effects either.
Read commentary →Physics: Delayed-choice quantum eraser
Delayed-choice quantum eraser By: Marlan Scully (1999) A delayed-choice quantum eraser experiment is an elaboration on the quantum eraser experiment that incorporates concepts considered in John Archibald Wheeler's delayed-choice experiment.
Read commentary →Physics: 2022 Nobel Prize in Physics
2022 Nobel Prize in Physics Awarded to: Alain Aspect, John F. Clauser, Anton Zeilinger Experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.
Read commentary →Physics: 1923 Nobel Prize in Physics
1923 Nobel Prize in Physics Awarded to: Robert Andrews Millikan His work on the elementary charge of electricity and on the photoelectric effect.
Read commentary →Physics: Uncertainty principle formalized
1927: Uncertainty principle formalized The uncertainty principle, also known as Heisenberg's indeterminacy principle, is a fundamental concept in quantum mechanics.
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What is quantum mechanics in simple terms?
Quantum mechanics is the branch of physics that describes how particles behave at the subatomic scale. At this scale, the rules are completely different from everyday physics: energy comes in discrete packets (quanta), particles have a probability distribution of locations rather than definite positions, and the act of observing a system affects it. It is the foundation of modern electronics, lasers, MRI machines, and nuclear energy.
Why is quantum mechanics so weird?
Because it describes a reality that doesn't match our everyday experience. In the quantum world, a particle can be in two states simultaneously (superposition) until observed, two particles can be instantaneously correlated regardless of distance (entanglement), and the uncertainty principle means you fundamentally cannot know both the position and momentum of a particle with arbitrary precision. Richard Feynman said: 'If you think you understand quantum mechanics, you don't understand quantum mechanics.'