A History of Modern Physics for Beginners

A very simple history of modern physics (1543-present), laid out so just about anyone can understand it. (Obviously a work in progress, because even the writer cannot understand it.)

• 1543: Nicolaus Copernicus places the sun at the gravitational center, starting a revolution in science.
• 1581: Galileo Galilei notices the timekeeping property of the pendulum.
• 1589: Galileo Galilei uses balls rolling on inclined planes to show that different weights fall with the same acceleration.
• 1593: Galileo invents the thermometer, though a very inaccurate one that was influenced not only by temperature but also atmospheric pressure.
• 1600: Dutchman Sacharias Jansen invents a single-lens microscope.
• 1600: In De Magnete, William Gilbert expanded on Gerolamo Cardano’s work (1550) and coined the New Latin word electricus from ἤλεκτρον (elektron), the Greek word for “amber” (from which the ancients knew a spark could be created by rubbing it with silk). Gilbert undertook a number of careful electrical experiments, in the course of which he discovered that many substances other than amber, such as sulphur, wax, glass, etc., were capable of manifesting electrostatic properties. Gilbert also discovered that a heated body lost its electricity and that moisture prevented the electrification of all bodies, due to the now well-known fact that moisture impairs the electrical insulation of such bodies. He also noticed that electrified substances attracted all other substances indiscriminately, whereas a magnet only attracted iron. The many discoveries of this nature earned for Gilbert the title of founder of the electrical sciences. He dispelled popular myths that the lodestone has curative powers or was a poison, or acted only by night. Others falsely believed the lodestone lost its attractive power in the presence of garlic, goat blood or diamond.
• 1604: Galileo deduces the law of falling bodies.
• 1604: Johannes Kepler describes how the eye focuses light.
• 1609: Kepler realized the orbit of Mars must be an ellipse, and publishes “Commentaries on the Motion of Mars”
• 1611: Marko Dominis discusses the rainbow in De Radiis Visus et Lucis.
• 1611: Kepler discovers total internal reflection, a small-angle refraction law, and thin lens optics.
• 1619: Kepler writes “The Harmony of the World”; in the work, Kepler discusses harmony and congruence in geometrical forms and physical phenomena. The final section of the work relates his discovery of the so-called “Third Law” of planetary motion.
• 1621: Willebrord Snell discovers Snell’s law of refraction.
• 1630: Cabaeus finds that there are two types of electric charges.
• 1632: Galileo publishes “Dialogue Concerning The Two Chief World Systems”, asserting that the Earth circles the Sun, and is immediately tried for heresy by the Catholic Church.
• 1637: René Descartes quantitatively derives the angles at which primary and secondary rainbows are seen with respect to the angle of the Sun’s elevation.
• 1638: Galileo publishes Dialogues Concerning Two New Sciences.
• 1640: Ismael Bullialdus suggests an inverse-square gravitational force law.
• 1643: Evangelista Torricelli develops the mercury barometer.
• 1646: The first usage of the word electricity is ascribed to Sir Thomas Browne’s work Pseudodoxia Epidemica.
• 1650: Otto von Guericke, the mayor of Magdeburg since 1646, builds the first vacuum pump, disproving Aristotle’s notion that “nature abhors a vacuum”.
• 1657: von Guericke demonstrated the effects of atmospheric pressure.
• 1657: Christian Huygens develops a clock regulated by a pendulum.
• 1657: Pierre de Fermat introduces the principle of least time into optics.
• 1658: Robert Hooke finds that a spiral spring vibrates with a regular period in the same way as a pendulum. This same year, he perfects the air pump.
• 1658: Huygens experimentally discovers that balls placed anywhere inside an inverted cycloid reach the lowest point of the cycloid in the same time and thereby experimentally shows that the cycloid is the isochrone, a figure with the curve for which the time taken by an object sliding without friction in uniform gravity to its lowest point is independent of its starting point.
• 1659: Christiaan Huygens coined the term “centrifugal force” in his “De Vi Centrifiga”
• 1660: Otto von Guericke invented an early electrostatic generator. By the end of the 17th Century, researchers had developed practical means of generating electricity by friction by the use of an electrostatic generator, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies of the new science of electricity.
• 1660: Robert Boyle experimentally discovers Boyle’s Law, relating the pressure and volume of a gas (published 1662). JD Bernal later said, “Boyle’s Law is the first physical law in science: all the other laws are essentially mathematical laws or, at the most, mechanical laws.” [Bernal: 254]
• 1665: Robert Hooke states, “Heat being nothing else but a very brisk and vehement agitation of the parts of a body.”
• 1665: Francesco Maria Grimaldi highlights the phenomenon of diffraction.
• 1665: Isaac Newton introduces an inverse-square universal law of gravitation uniting terrestrial and celestial theories of motion and uses it to predict the orbit of the Moon and the parabolic arc of projectiles.
• 1667: Johann Joachim Becher stated the now-defunct scientific theory that postulated the existence of a fire-like element called “phlogiston” that was contained within combustible bodies and released during combustion. The theory was an attempt to explain processes such as combustion and the rusting of metals, which are now understood as oxidation, and which was ultimately disproved by Antoine Lavoisier in 1789.
• 1668: Isaac Newton succeeds in making the first reflecting telescope, a tiny instrument only 15cm long, but the direct ancestor of today’s huge astronomical reflecting telescopes.
• 1668: John Wallis suggests the law of conservation of momentum, which states that if no external force acts on a closed system of objects the momentum of the closed system is constant.
• 1669: Erasmus Bartholin finds double refraction.
• 1673: Ignace Pardies provides a wave explanation for refraction of light.
• 1675: Isaac Newton delivers his theory of light.
• 1675: Robert Boyle discovered that electric attraction and repulsion can act across a vacuum and does not depend upon the air as a medium. He also added resin to the then-known list of “electrics.”
• 1676: Olaus Roemer measures the speed of light by observing Jupiter’s moons.
• 1678: Hooke’s Law is discovered.
• 1678: Huygens publishes “Traite de la Lumiere”, which contained his wave or pulse theory of light.
• 1679: Denis Papin designed a steam digester which inspired the development of the piston-and-cylinder steam engine.
• 1684: After a discussion at the Royal Society between astronomer Edmond Halley, architect Sir Christopher Wren, and Robert Hooke, Halley visits Newton in Cambridge to solve how an inverse square law of attraction can explain the elliptical orbits for planets. Newton proves that planets moving under an inverse-square force law will obey Kepler’s laws.
• 1684: Isaac Newton coins the term “centripetal force” (vis centripita) in his discussions of gravity in his “De Motu Corporum”.
• 1686: Newton uses a fixed length pendulum with weights of varying composition to test the weak equivalence principle to 1 part in 1000.

The Age of Newtonian Mechanics Begins

• July 1687: Newton publishes “Mathematical Principles of Natural Philosophy”, featuring his three laws of motion.
• 1690: James Bernoulli shows that the cycloid is the solution to the isochrone problem.
• 1691: Johann Bernoulli shows that a chain freely suspended from two points will form a catenary, the curve that an idealized hanging chain or cable assumes when supported at its ends and acted on only by its own weight.
• 1691: James Bernoulli shows that the catenary curve has the lowest center of gravity that any chain hung from two fixed points can have.
• 1695: Guillaume Amontons improved the gas thermometer by using mercury instead of water and having the mercury rise and fall in a closed column, thus avoiding effects due to atmospheric pressure.
• 1696: Johann Bernoulli shows that the cycloid is the solution to the brachistochrone problem.
• 1698: Thomas Savery patented an early steam engine.
• 1702: Guillaume Amontons introduces the concept of absolute zero, based on observations of gases.
• 1704: Isaac Newton publishes “Opticks”, wherein he explains about the refraction of light and contended that light was made up of numerous small particles. This hypothesis could explain such features as light’s ability to travel in straight lines and reflect off surfaces. However, this proposed theory was known to have its problems: although it explained reflection well, its explanation of refraction and diffraction was less satisfactory. In order to explain refraction, Newton postulated an “Aethereal Medium” transmitting vibrations faster than light, by which light, when overtaken, is put into “Fits of easy Reflexion and easy Transmission,” which he supposed caused the phenomena of refraction and diffraction.
• 1707: The Irish bishop George Berkeley takes issue with the notion of absolute space, declaring that “motion cannot be understood except in relation to our or some other body”.
• 1708: Brook Taylor obtained a remarkable solution of the problem of the “centre of oscillation” fundamental to the development of wave mechanics and derives the fundamental frequency of a stretched vibrating string in terms of its tension and mass per unit length by solving an ordinary differential equation, which, however, remained unpublished until May 1714.
• 1715: In Methodus Incrementorum Directa et Inversa, Brook Taylor added a new branch to the higher mathematics, now designated the “calculus of finite differences.” Among other ingenious applications, he used it to determine the form of movement of a vibrating string, first successfully reduced by him to mechanical principles. The same work contained the celebrated formula known as Taylor’s theorem, the importance of which remained unrecognized until 1772, when J. L. Lagrange realized its powers and termed it “le principal fondement du calcul différentiel” (“the main foundation of differential calculus”). Taylor’s work thereby provided the cornerstone of the calculus of wave mechanics.
• 1722: René Antoine Ferchault de Réaumur demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon.
• 1728: James Bradley discovers the aberration of starlight and uses it to determine that the speed of light is about 283,000 km/s.
• 1729: Stephen Gray conducted a series of experiments that demonstrated the difference between conductors and non-conductors (insulators). From these experiments he classified substances into two categories: “electrics” like glass, resin and silk, and “non-electrics” (what would now be called conductors) like metal and water. Although Gray was the first to discover and deduce the property of electrical conduction, he incorrectly stated that “electrics” conducted charges while “non-electrics” held the charge.
• 1732: C. F. duFay conducted several experiments and concluded that all objects, except metals, animals, and liquids, could be electrified by rubbing them and that metals, animals and liquids could be electrified by means of an “electric machine” (the name used at the time for electrostatic generators), thus discrediting Gray’s “electrics” and “non-electrics” classification of substances.
• 1733: Daniel Bernoulli derives the fundamental frequency and harmonics of a hanging chain by solving an ordinary differential equation.
• 1734: Daniel Bernoulli solves the ordinary differental equation for the vibrations of an elastic bar clamped at one end.
• 1737: C.F. du Fay and Francis Hauksbee independently discovered what they believed to be two kinds of frictional electricity: one generated from rubbing glass, the other from rubbing resin. From this, Du Fay theorized that electricity consists of two “electrical fluids”: “vitreous” and “resinous”, that are separated by friction, and that neutralize each other when combined. This two-fluid theory would later give rise to the concept of positive and negative electrical charges devised by Benjamin Franklin.
• 1738: Daniel Bernoulli publishes “Hydrodynamica”, a theoretical and practical study of equilibrium, pressure and velocity in fluids.
• 1739: Leonhard Euler solves the ordinary differential equation for a forced harmonic oscillator and notices the resonance phenomenon.
• 1740: In Mémoire sur la réfraction des corps solides, Jean le Rond d’Alembert explains the process of refraction.
• 1742: Colin Maclaurin discovers his uniformly rotating self-gravitating spheroids.
• 1745: Charles DuFay discovers that electric charges can be either positive or negative.
• 1745: At Leiden University, Pieter van Musschenbroek invented the Leyden jar, a type of capacitor (also known as a “condensor”) for electrical energy in large quantities.
• 1746: Leonhard Euler develops the wave theory of light refraction and dispersion.
• 1747: Pierre Louis Maupertuis applies minimum principles to mechanics.
• 1747: While experimenting with a Leyden jar (1745), William Watson discovered the concept of an electrical potential (voltage) when he observed that a discharge of static electricity caused the electric current earlier observed by Stephen Gray to occur.
• 1752: Benjamin Franklin identified lightning with electricity when he discovered that lightning conducted through a metal key could be used to charge a Leyden jar, thus proving that lightning was an electric discharge and current (1747). He is also attributed with the convention of using “negative” and “positive” to denote an electrical charge or potential.
• 1758: John Dollond publishes an “Account of some experiments concerning the different refrangibility of light”, describing the experiments that led him to the achievement with which his name is specially associated, the discovery of a means of constructing achromatic lenses by the combination of crown and flint glasses, which reduces chromatic aberration (color defects).
• 1759: Leonhard Euler solves the partial differential equation for the vibration of a rectangular drum.
• 1760: Johann Heinrich Lambert published a book on photometry, the Photometria. From the assumption that light travels in straight lines, he showed that illumination was proportional to the strength of the source, inversely proportional to the square of the distance of the illuminated surface and the sine of the angle of inclination of the light’s direction to that of the surface. These results were supported by experiments involving the visual comparison of illuminations and used for the calculation of illumination. In Photometria Lambert also formulated the law of light absorption—the Beer–Lambert law) and introduced the term albedo.
• 1761: Joseph Black establishes the concept of latent heat (ice absorbs heat without changing its temperature when melting).
• 1764: Euler examines the partial differential equation for the vibration of a circular drum and finds one of the Bessel function solutions.
• 1766: Henry Cavendish is the first to recognize hydrogen gas as a distinct substance, by identifying the gas from a metal-acid reaction as “flammable air” and further finding in 1781 that the gas produces water when burned.
• 1767: Joseph Priestley proposes an electrical inverse-square law.
• 1771: Luigi Galvani invented the voltaic cell. Galvani made this discovery when he noted that two different metals (copper and zinc for example) were connected together and then both touched to different parts of a nerve of a frog leg at the same time, a spark was generated which made the leg contract. Although he incorrectly assumed that the electrical current was proceeding from the frog as some kind of “animal electricity,” his invention of the voltaic cell was fundamental to the development of the electric battery.
• 1772: Antoine Lavoisier showed that diamonds are a form of carbon, when he burned samples of carbon and diamond then showed that neither produced any water and that both released the same amount of carbon dioxide per gram.
• 1772: Carl Scheele showed that graphite, which had been thought of as a form of lead, was instead a type of carbon.
• 1772: Black’s student Daniel Rutherford discovers nitrogen, calling it noxious air or fixed air because this gas constituted a fraction of air that did not support combustion. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as “mephitic air” or azote, from the Greek word άζωτος (azotos) meaning “lifeless”. Animals died in it, and it was the principal component of air in which animals had suffocated and flames had burned to extinction.
• 1772: Scheele produced oxygen gas by heating mercuric oxide and various nitrates by about 1772. Scheele called the gas ‘fire air’ because it was the only known supporter of combustion, and wrote an account of this discovery in a manuscript he titled Treatise on Air and Fire, which he sent to his publisher in 1775. However, that document was not published until 1777.
• 1776: Henry Cavendish demonstrates the existence of hydrogen as a substance.
• 1776: John Smeaton publishes a paper on experiments related to power, work, momentum, and kinetic energy, supporting the conservation of energy.
• 1777: Carl Wilhelm Scheele distinguishes heat transfer by thermal radiation from that by convection and conduction.
• 1778: Scheele and Antoine Lavoisier discover that air is composed mostly of nitrogen and oxygen.
• 1781: Joseph Priestley creates water by igniting hydrogen and oxygen.
• 1782: Conservation of matter, Antoine Lavoisier
• 1783: Lavoisier discovers oxygen and develops an explanation for combustion; in his paper “Réflexions sur le phlogistique”, he deprecates the phlogiston theory and proposes a caloric theory.
• 1784: Jan Ingenhousz describes Brownian motion of charcoal particles on water.
• 1784: Henry Cavendish discovered the inductive capacity of dielectrics (insulators) and, as early as 1778, measured the specific inductive capacity for beeswax and other substances by comparison with an air condenser.
• 1784: Coulomb devised the torsion balance, by means of which he discovered what is known as Coulomb’s law: the force exerted between two small electrified bodies varies inversely as the square of the distance; not as Franz Aepinus in his theory of electricity had assumed, merely inversely as the distance.
• 1786: Luigi Galvani discovers “animal electricity” and postulates that animal bodies are storehouses of electricity. This was the beginning of the modern battery.
• 1787: Inverse square law for electric charges and magnetism is confirmed by Charles Coulomb.
• 1788: Joseph Louis Lagrange presents Lagrange’s equations of motion in Mécanique Analytique.
• 1789: Antoine Lavoisier states the law of conservation of mass: the mass of a closed system (in the sense of a completely isolated system) will remain constant over time.
• 1791: Pierre Prévost shows that all bodies radiate heat, no matter how hot or cold they are.
• 1793: Alessandro Volta shows that a flow of electricity occurs when two metals are brought in contact with moisture, contesting the ideas of Luigi Galvani.
• 1796: Carl Friedrich Gauss constructs a seventeen-sided regular polygon using only a ruler and compass, the first construction of a regular figure in modern times.
• 1797: Volta invents the copper-zinc battery.
• 1798: Cavendish measures the force of gravity between two masses, and announced his fairly accurate determination of Newton’s gravitational constant, thereby deriving the density and mass of the Earth.
• 1798: Count Rumford (Benjamin Thompson) performs measurements of the frictional heat generated in boring cannons and develops the idea that heat is a form of kinetic energy; his measurements refute caloric theory, but are imprecise enough to leave room for doubt.
• 1798: Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven. He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald. Discovered beryllium in emerald (beryl) when he dissolved the beryl in sodium hyrdoxide, separating the aluminum hydroxide and beryllium compound from the silicate crystals, and then dissolving the aluminum hydroxide in another alkali solution to separate it from the beryllium.
• 1800: Volta invents “wet cells” or the “voltaic pile”, specifically to disprove Galvani’s animal electricity theory.
• 1800: Johann Wilhelm Ritter electrolyzed water to produce hydrogen and oxygen. Apparently, William Nicholson and Anthony Carlisle did the same thing this year.
• 1800: William Herschel discovers infrared radiation from the Sun.
• 1801: Wave theory of light and the principle of interference, Young
• 1801: Thomas Young proposes the three-color theory of vision.
• 1801: Gauss makes a remarkable prediction of the position in which the asteroid Ceres could be found, using his theory of least squares.
• 1801: Johann Wilhelm Ritter made the hallmark observation that invisible rays just beyond the violet end of the visible spectrum were especially effective at lightening silver chloride-soaked paper. He called them “oxidizing rays” to emphasize chemical reactivity and to distinguish them from “heat rays” at the other end of the invisible spectrum (both of which were later determined to be photons). The simpler term “chemical rays” was adopted shortly thereafter to describe the heat rays, and it remained popular throughout the 19th century. The terms chemical and heat rays were eventually dropped in favor of ultraviolet and infrared radiation, respectively.
• 1802: John Dalton deduced Jacques Charles’ Law of gas, showing the dependency between temperature and volume, but the first to publish it was Gay-Lussac, leading to it being called Gay-Lussac’s law in France.
• 1802: Ritter develops a dry battery.
• 1802: Gian Domenico Romagnosi notes that a nearby voltaic pile deflects a magnetic needle. His account is largely overlooked.
• 1803: John Dalton introduces atomic ideas into chemistry and states that matter is composed of atoms of different weights.
• 1803: Continuing the work of his uncle, Luigi Galvani, Giovanni Aldini made a public demonstration of the electro-stimulation technique of deceased limbs when he performed on the executed criminal George Forster at Newgate in London. This was said to be a direct influence on Mary Shelley’s “Frankenstein”.
• 1804: Sir John Leslie observes that a matte black surface radiates heat more effectively than a polished surface, suggesting the importance of black body radiation.
• 1805: William Hyde Wollaston defends the conservation of energy in On the Force of Percussion.
• 1805: Thomas Young conducts Double-slit experiment (approximate time).
• 1806: Volta, employing a voltaic pile of approximately 250 cells, or couples, decomposed potash and soda, showing that these substances were respectively the oxides of potassium and sodium, which metals previously had been unknown. These experiments were the beginning of electrochemistry.
• 1808: Etienne-Louis Malus discovers polarization by reflection.
• 1808: John Dalton defends caloric theory in A New System of Chemistry and describes how it combines with matter, especially gases; he proposes that the heat capacity of gases varies inversely with atomic weight.
• 1809: Malus publishes the law of Malus which predicts the light intensity transmitted by two polarizing sheets.
• 1810: Sir John Leslie freezes water to ice artificially.
• 1811: Amadeo Avogadro hypothesized that two given samples of an ideal gas, at the same temperature, pressure and volume, contain the same number of molecules. Thus, the number of molecules or atoms in a specific volume of gas is independent of their size or the molar mass of the gas. He wrote this in his “Essay on Determining the Relative Masses of the Elementary Molecules of Bodies and the Proportions by Which They Enter These Combinations”.
• 1811: Francois Arago invented the polariscope, with which he was able to measure the degree of polarization of light rays.
• 1813: Peter Ewart supports the idea of the conservation of energy in his paper “On the measure of moving force”. The paper strongly influences Dalton and his pupil, James Joule.
• 1814: Wave theory of light, interference, Fresnel
• 1814: Andre-Marie Ampere independently arrived at what is now known as Avogadro’s hypothesis of the molecular constitution of gases. (See 1811)
• 1815: William Nicol develops a method of preparing extremely thin sections of crystals and rocks for microscopial study. His technique (which involved cementing the specimen to a glass slide and then carefully grinding until it was extremely thin) made it possible to view mineral samples by transmitted rather than reflected light and therefore enabled the minerals’ internal structures to be seen.
• 1815: William Prout hypothesizes that all matter is built up from hydrogen, adumbrating the proton.
• 1816: David Brewster patents the kaleidoscope.
• 1816: Brewster discovers stress birefringence, the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride.
• 1817: Arfwedson, then working in the laboratory of Berzelius, detected the presence of a new element while analyzing petalite ore. This element formed compounds similar to those of sodium and potassium, though its carbonate and hydroxide were less soluble in water and more alkaline. Berzelius gave the alkaline material the name “lithos,” from the Greek word λιθoς (transliterated as lithos, meaning “stone”), to reflect its discovery in a solid mineral, as opposed to sodium and potassium, which had been discovered in plant tissues.
• 1818: Simeon Poisson predicts the Poisson-Arago bright spot at the center of the shadow of a circular opaque obstacle, Arago verifies its existence the same year.
• 1819: Charles Bernard Desormes and Nicolas Clement publish a classic paper describing the first determination of the ratio of the specific heat capacity of a gas at constant pressure to its specific heat capacity at constant volume. Their work influenced Carnot.
• 1819: Pierre Louis Dulong and Alexis Thérèse Petit give the Dulong-Petit law for the specific heat capacity of a crystal. An equivalent statement of the Dulong-Petit law in modern terms is that, regardless of the nature of the substance or crystal, the specific heat capacity (measured in joule per kelvin per kilogram) is equal to 3R/M, where R is the gas constant (measured in joule per kelvin per mole) and M is the molar mass (measured in gram per mole).
• April 21, 1820: During a lecture, Hans Christian Oersted noticed a compass needle deflected from magnetic north when an electric current from a battery was switched on and off, confirming a direct relationship between electricity and magnetism.
• 1820: Evidence for electromagnetic interactions, Biot, Savart
• 1820: Arago found that an electric current produces temporary magnetization in iron, a discovery crucial to the later development of electromagnets, electric relays and loudspeakers.
• 1820: John Frederic Daniell invents a new type of dew-point hygrometer for measuring humidity.
• 1820: John Herapath develops some ideas in the kinetic theory of gases but mistakenly associates temperature with molecular momentum rather than kinetic energy; his work receives little attention other than from Joule.
• 1821: Gauss invents the heliotrope.
• 1821: Augustin Fresnel Demonstrated via mathematical methods that polarization could be explained only if light was entirely transverse, with no longitudinal vibration whatsoever. This finding was later very important to Maxwell’s equations and to Einstein’s Theory of Special Relativity. His use of two plane mirrors of metal, forming with each other an angle of nearly 180°, allowed him to avoid the diffraction effects caused (by the apertures) in the experiment of F. M. Grimaldi on interference. This allowed him to conclusively account for the phenomenon of interference in accordance with the wave theory. With François Arago he studied the laws of the interference of polarized rays. He obtained circularly polarized light by means of a rhombus of glass, known as a Fresnel rhomb, having obtuse angles of 126° and acute angles of 54°.
• 1821: William Hamilton begins his analysis of Hamilton’s characteristic function.
• 1822: French mathematician Joseph Fourier publishes work on the flow of heat, and formally introduces the use of dimensions for physical quantities in his Théorie Analytique de la Chaleur.
• 1822: Marc Séguin writes to John Herschel supporting the conservation of energy and kinetic theory.
• 1824: Sadi Carnot analyzes the efficiency of steam engines using caloric theory; he develops the notion of a reversible process and, in postulating that no such thing exists in nature, lays the foundation for the second law of thermodynamics, and initiating the science of thermodynamics.
• 1824: Arago discovered that a rotating non-magnetic metal disc, for example of copper, deflects a magnetic needle placed above it.
• 1825: Fresnel phenomenologically explains optical activity by introducing circular birefringence.
• 1825: William Sturgeon constructed the first true electromagnet. It was made of soft iron bent into the shape of a horseshoe five inches high, and was wound with eighteen turns of wire. On passing a current through the wire it was found that the electromagnet could lift twenty times its own weight (seven ounces lifting nine pounds).
• 1827: Ampere publishes “Notes on the Mathematical Theory of Electrodynamic Phenomena Deduced Solely from Experiment” in which he enunciated precise mathematical formulations of electromagnetism, notably Ampere’s Law — an equation that relates the magnetic force produced by two parallel current-carrying conductors to the product of their currents and the distance between the conductors.
• 1827: Georg Ohm publishes “The Galvanic Circuit Investigated Mathematically”, which included Ohm’s Law. Ohm’s law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.
• 1827: Robert Brown discovers Brownian motion, the random movement of fine particles which can be seen through a microscope, when studying a suspension of pollen grains in water.
• 1828: Nicol invents the Nicol prism, an optical device used to generate a beam of polarized light. It consists of a rhombohedral crystal of Iceland spar (a variety of calcite) that has been cut at a 68° angle, split diagonally, and then joined again using Canada balsam (a transparent liquid).
• 1830: Daniell invents a pyrometer for measuring the temperatures of furnaces.
• 1830: Nicolas Léonard Sadi Carnot establishes the First Law of Thermodynamics, but his notebooks are not published until 1927, so he receives no credit.
• 1831: Macedonio Melloni demonstrates that black body radiation can be reflected, refracted, and polarised in the same way as light.
• October 1831: Michael Faraday constructs the first electric generator.
• 1833: Heinrich Lenz states that an induced current in a closed conducting loop will appear in such a direction that it opposes the change that produced it (Lenz’s law).
• 1833: William Hamilton stated a reformulation of classical mechanics that arose from Lagrangian mechanics, a previous reformulation of classical mechanics introduced by Joseph Louis Lagrange in 1788, but which can be formulated without recourse to Lagrangian mechanics using symplectic spaces (see Mathematical Formalism). As with Lagrangian mechanics, Hamilton’s equations provide a new and equivalent way of looking at classical mechanics. Generally, these equations do not provide a more convenient way of solving a particular problem. Rather, they provide deeper insights into both the general structure of classical mechanics and its connection to quantum mechanics as understood through Hamiltonian mechanics, as well as its connection to other areas of science.
• 1833: Faraday announced his important law of electrochemical equivalents, viz.: “The same quantity of electricity — that is, the same electric current — decomposes chemically equivalent quantities of all the bodies which it traverses; hence the weights of elements separated in these electrolytes are to each other as their chemical equivalents.”
• 1834: Heinrich Lenz applied an extension of the law of conservation of energy to the non-conservative forces in electromagnetic induction to give the direction of the induced electromotive force (emf) and current resulting from electromagnetic induction. The law provides a physical interpretation of the choice of sign in Faraday’s law of induction (1831), indicating that the induced emf and the change in flux have opposite signs. Stated another way, Lenz’s Law says that when an induced current flows it always does so in such a direction as to oppose the motion inducing the current.
• 1834: Carl Jacobi discovers his uniformly rotating self-gravitating ellipsoids.
• 1834: John Russell observes a nondecaying solitary water wave (soliton) in the Union Canal near Edinburgh and uses a water tank to study the dependence of solitary water wave velocities on wave amplitude and water depth.
• 1834: Émile Clapeyron popularises Carnot’s work through a graphical and analytic formulation. He also combined Boyle’s Law, Charles’s Law, and Gay-Lussac’s Law to produce a Combined Gas Law. PV/T = k.
• 1834: Peltier discovered what is now called the Peltier effect: the heating effect of an electrical current at the junction of two different metals.
• 1835: Gaspard Gustave de Coriolis examines theoretically the mechanical efficiency of waterwheels, and published his famous paper on the nature of relative motion in moving systems (the Coriolis Effect).
• 1835: Joseph Henry develops the relay (later to be used in electric telegraphy).
• 1835: William Hamilton states Hamilton’s canonical equations of motion.
• 1838: Lines of force, fields, Michael Faraday
• 1838: Earth’s magnetic field, Weber
• 1838: Arago published a method for determining the speed of light using a rotating mirror.
• 1838: Richard Laming hypothesized a subatomic particle carrying electric charge.
• 1839: Marc Seguin makes a rough estimate of the mechanical equivalent of heat.
• 1841: Julius Robert von Mayer, an amateur scientist, writes a paper on the conservation of energy but his lack of academic training leads to its rejection.
• 1842: Christian Doppler proposes the Doppler effect, the change in frequency of a wave for an observer moving relative to the source of the wave.
• 1842: Mayer makes a connection between work, heat, and the human metabolism based on his observations of blood made while a ship’s surgeon; he calculates the mechanical equivalent of heat.
• 1842: William Robert Grove demonstrates the thermal dissociation of molecules into their constituent atoms, by showing that steam can be disassociated into oxygen and hydrogen, and the process reversed.
• 1843: James Prescott Joule announces the determination of the amount of work required to produce a unit of heat.
• 1843: John James Waterston fully expounds the kinetic theory of gases, but is ridiculed and ignored.
• 1845: Faraday rotation (light and electromagnetic)
• 1845: Armand Hippolyte Louis Fizeau takes the first detailed photographs of the Sun.
• 1845: Henri Victor Regnault added Avogadro’s Law to the Combined Gas Law to produce the Ideal Gas Law. PV = nRT.
• 1846: Urbain Le Verrier and John Couch Adams, studying Uranus orbit, independently prove that another, farther planet must exist. Neptune was found at the predicted moment and position.
• 1846: Karl-Hermann Knoblauch publishes De calore radiante disquisitiones experimentis quibusdam novis illustratae.
• 1846: Grove publishes an account of the general theory of the conservation of energy in On The Correlation of Physical Forces.
• 1847: Hermann von Helmholtz formally states the law of conservation of energy, the first law of thermodynamics. The law expresses that energy can be changed from one form to another, but cannot be created nor destroyed.
• 1847: Fizeau finds that heat rays from the Sun undergo interference and that radiant heat therefore behaves as a wave motion.

The Age of Thermodynamics Begins

• 1848: Fizeau suggests that the Doppler effect would apply to the light received from Stars, motion away from the Earth causing a red shift in the spectral lines and motion towards the Earth producing a blue shift.
• 1848: Herman Ludwig Ferdinand von Helmholtz finds that animal heat and muscle action are generated by chemical changes in the muscles.
• 1848: Lord Kelvin sets absolute zero at -273 degrees Celsius, extending the concept of absolute zero from gases to all substances.
• 1849: Fizeau determines a reasonably accurate estimation of the speed of light (315,000 km/s).
• 1849: William John Macquorn Rankine calculates the correct relationship between saturated vapour pressure and temperature using his hypothesis of molecular vortices.
• 1849: James Thomson determined the lowering of melting point caused by pressure on ice.
• 1850: Fizeau discovers that light travels faster through air than through water.
• 1850: The second law of thermodynamics was formulated by Rudolph Clausius and Lord Kelvin, based on work done by Nicolas Leonard Sadi Carnot, abandoning the caloric theory, but preserving Carnot’s principle.
• 1850: Rankine uses his vortex theory to establish accurate relationships between the temperature, pressure, and density of gases, and expressions for the latent heat of evaporation of a liquid; he accurately predicts the surprising fact that the apparent specific heat of saturated steam will be negative.
• 1851: Helmholtz invents the ophtalmoscope.
• 1851: Edward Sabine discovers a 10-11 year periodic fluctuation in the number of magnetic storms.
• 1851: Jean Bernard Léon Foucault shows the Earth’s rotation with a huge, 62-pound pendulum (Foucault pendulum).
• 1852: Kelvin produces the idea that mechanical energy tends to dissipate as heat, or that a rapidly expanding gas cools, later named the Joule–Thomson effect.
• 1852: Foucault invents the gyroscope.
• 1852: George Gabriel Stokes explains fluorescence.
• 1852: Frankland: Initiated the theory of valency by proposing that each element has a specific “combining power”, e.g. some elements such as nitrogen tend to combine with three other elements (e.g. NO3) while others may tend to combine with five (e.g. PO5), and that each element strives to fulfill its combining power (valency) quota.
• 1853: Anders Jonas Angstrom published “Optical Investigations”, which contained his principle of spectrum analysis.
• 1854: David Alter put forward the idea that each element has a characteristic spectrum, and that spectroscopic analysis of a substance can therefore be used to identify the elements present.
• 1854: Helmholtz predicts the age of the Earth to be 25 million years, based on the idea that the Sun gained its energy by gravitational contraction. Today, of course, we know he was far too low.
• 1854: Clausius establishes the importance of dQ/T (Clausius’s theorem), but does not yet name the quantity.
• 1854: Rankine introduces his thermodynamic function, later identified as entropy.
• 1855: Helmholtz invents the ophthalmometer.
• 1855: Le Verrier observes a 35 arcsecond per century excess precession of Mercury’s orbit and attributes it to another planet, named Vulcan, inside Mercury’s orbit. The planet was never found. (Mercury’s orbit has now been explained by Albert Einstein’s theory of general relativity.)
• 1856: August Krönig publishes an account of the kinetic theory of gases, probably after reading Waterston’s work of 1843.
• 1857: Clausius becomes the first to propose that an electric current could induce the dissociation of materials, a concept which was eventually established by Svante Arrhenius.
• 1857: Waterston predicts the temperature of the Sun to be 13 million degrees. Today, we believe the center is closer to 27 million degrees.
• 1858: Julius Plücker published the first of his classical researches on the action of magnets on the electric discharge of rarefied gases in Geissler tubes. He found that the discharge caused a fluorescent glow to form on the glass walls of the vacuum tube, and that the glow could be made to shift by applying a magnetic field to the tube. It was later shown by Johann Wilhelm Hittorf that the glow was produced by rays emitted from one of the electrodes (the cathode).
• 1859: Ludwig Boltzmann writes a paper on the kinetic theory of gases.
• 1859: Gustav Kirchhoff shows that energy emission from a black body is a function of only temperature and frequency.
• 1860: Robert Bunsen discovers cesium (element 55) by the newly developed method of flame spectroscopy.
• 1861: Bunsen discovers rubidium (element 37), again by the newly developed method of flame spectroscopy.
• 1861: James Clerk Maxwell produces the first color photograph using the three-color process.
• 1862: Angstrom announced his inference (discovery) that hydrogen was present in the Sun.
• 1862: Foucault outdoes his former partner Fizeau and makes a more accurate estimation of the speed of light (298,000 km/s).
• 1862: Kelvin predicts the age of the Earth to be 100 million years old, based on the estimated rate of cooling from the time the Earth formed. He was closer than Helmholtz, but today we know he was still quite a ways off.
• 1862: “Disgregation”, a precursor of entropy, was defined by Rudolf Clausius as the magnitude of the degree of separation of molecules of a body.
• 1863: Thomas Andrews established the concepts of critical temperature and critical pressure, showing that a substance passes from vapor to liquid state without any breach of continuity. He coined the term “critical point” in 1869.
• 1865: Clausius introduces the modern macroscopic concept of entropy.
• 1865: Josef Loschmidt applies Maxwell’s theory to estimate the number-density of molecules in gases, given observed gas viscosities.
• 1866: August Adolph Kundt developed a valuable method for the investigation of aerial waves within pipes, based on the fact that a finely divided powder, lycopodium for example, when dusted over the interior of a tube in which is established a vibrating column of air, tends to collect in heaps at the nodes, the distance between which can thus be ascertained. An extension of the method renders possible the determination of the velocity of sound in different gases.
• 1866: Georges Leclanche invents the dry cell (the kind of battery used today in calculators and portable radios).
• 1867: After observing Scottish physicist Peter Tait’s experiments involving smoke rings, Lord Kelvin came to the idea that atoms were knots of swirling vortices in the ether. Chemical elements would thus correspond to knots and links. This idea would give rise to “knot theory”.
• December 11, 1867: Maxwell asks whether Maxwell’s demon could reverse irreversible processes. (Huh?)
• 1867: Angstrom becomes the first person to explore the spectrum of the Aurora Borealis.
• 1868: Angstrom publishes “Researches on the Solar System”, where he presented measurements of the wavelengths of more than 100 Fraunhofer.
• 1868: Boltzmann publishes a paper on thermal equilibrium in gases, citing and extending the work of Maxwell.
• October 20, 1868: Frankland observed a yellow line in the solar spectrum, which he named the “D3 Fraunhofer line” because it was near the known D1 and D2 lines of sodium. He correctly concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and Frankland named the element with the Greek word for the Sun, ἥλιος, “helios.”
• 1869: Angstrom publishes his map of the normal solar spectrum.
• 1870: Kelvin develops an absolute electrometer.
• 1870: Clausius proves the scalar virial theorem.
• 1871: Lord Rayleigh explains that the blue color of the sky arises from the scattering of light by dust particles in the air.
• 1871: Dmitri Ivanovich Mendeleev systematically examines the periodic table and predicts the existence of gallium, scandium, and germanium.
• 1872: Ernst Abbe developed the substage condenser for illuminating objects under high-power magnification.
• 1872: James Dewar invented the vacuum flask (basically a Thermos) as an insulating container in the course of an investigation of hydrogen-absorbed palladium.
• 1873: Maxwell introduces the concept of the electromagnetic “field” in his “Treatise on Electricity and Magnetism”. (Devised earlier in 1864?)
• 1873: Johannes van der Waals introduces the idea of weak attractive forces between molecules.
• 1873: Jules Célestin Jamin constructed the most powerful permanent magnet in the world. It weighed a hundredweight (roughly 100-112 pounds) and could support a load ten times that.
• 1874: Karl Ferdinand Braun publishes a paper describing his research on mineral metal sulphides, some of which, he found, conduct electricity in one direction only.
• 1874: George Johnstone Stoney hypothesizes a minimum unit of electric charge (which he calls “an absolute unit of electricity”). In 1891, he coins the word “electron” for it.
• 1875: William Crookes devises the radioscope (or radiometer).
• 1875: John Kerr demonstrated that birefringence or double refraction occurs in glass and other insulators when subjected to an intense electric field.
• 1876: William Kingdon Clifford suggests that the motion of matter may be due to changes in the geometry of space.
• 1876: Josiah Willard Gibbs publishes the first of two papers (the second appears in 1878) which discuss phase equilibria, statistical ensembles, the free energy as the driving force behind chemical reactions, and chemical thermodynamics in general.
• 1876: Loschmidt criticises Boltzmann’s H theorem as being incompatible with microscopic reversibility (Loschmidt’s paradox).
• 1877: Boltzmann publishes his famous equation “S=k log W”, describing the relation between entropy and probability.
• 1877: Louis Paul Cailletet liquefies oxygen, with Raoul Pictet doing the same thing independently.
• 1878: Henry Augustus Rowland investigated the value of the ohm, and published a value very close to that accepted today.
• 1879: Crookes publishes a paper on the movement of cathode rays in discharge tubes.
• 1879: Josef Stefan discovers the Stefan-Boltzmann radiation law of a black body and uses it to calculate the first sensible value of the temperature of the Sun’s surface to be 5700 K.
• 1882: Rowland develops the concave diffraction grating, which have been of enormous advantage to astronomical spectroscopy.
• 1882: Simon Newcomb observes a 43 arcsecond per century excess precession of Mercury’s orbit.
• 1884: Boltzmann derives Stefan radiation law
• 1884: Sir William Thomson (Lord Kelvin) says, “The luminiferous aether is… the only substance we are confident of in dynamics. One thing we are sure of, and that is the reality and substantiality of the luminiferous aether.”
• 1884: Edwin Abbott writes “Flatland: A Romance of Many Dimensions”, a satirical novella that explores the idea of additional dimensions we cannot be aware of.
• 1885: Johann Jakob Balmer publishes an equation that described the four visible spectral lines of hydrogen (all that were then known) and also predicted the existence of a fifth line at the limit of the visible spectrum, which was soon detected and measured. He took up the study at the suggestion of physicist Eduard Hagenbach, also of Basel, Switzerland.
• 1886: Ernst Abbe calculated how to correct chromatic aberration, using Schott’s special glasses and, later, fluorite to make microscope objective lenses, culminating in the apochromatic lens system.
• 1886: Eugene Goldstein discovered that discharge tubes with a perforated cathode (negative electrode) also emit a glow at the cathode end. Goldstein concluded that in addition to the already-known cathode rays (later recognized as electrons) moving from the negatively-charged cathode toward the positively-charged anode, there is another ray that travels in the opposite direction. Because these latter rays passed through the holes, or channels, in the cathode, Goldstein called them “Kanalstrahlen,” or canal rays. He determined that canal rays are composed of positive ions whose identity depends on the residual gas inside the tube. It was another of Helmholtz’s students, Wilhelm Wien, who later conducted extensive studies of canal rays, and in time this work would become part of the basis for mass spectrometry.
• 1887: Albert Michelson and Edward Morley demonstrated that there was no evidence for ether. They fired two light beams at right angles, supposing that the speed of light is a fixed number relative to the ether. As the light beams did not change speed based on their direction, this suggested that there is no ether. Interestingly, Michelson never accepted his own findings, no matter how many times he replicated the experiment until his death in 1931.
• 1887-8: Electromagnetic (radio) waves are discovered by Heinrich Rudolf Hertz, after working with Maxwell’s equations of electricity. His receiver consisted of a coil with a spark gap, where a spark would be seen upon detection of EM waves transmitted from another spark gap source.
• 1889: Loránd Eötvös uses a torsion balance to test the weak equivalence principle to 1 part in one billion.
• 1890: Charles Vernon Boys invents the radiomicrometer to detect infrared radiation.
• 1891: Dewar finds that both liquid oxygen and ozone are magnetic.
• 1892: George Francis FitzGerald proposed that the Michelson-Morley result of 1887 — or lack thereof — could be accounted for by assuming that a fast-moving object diminishes in length, and that light emitted by it does indeed have a different velocity but travels over a shorter path, and so seems to have a constant velocity no matter what the direction of motion.
• February 1893: Wilhelm Wien discovers the displacement law for blackbody radiation.
• 1893: Working off of the Michelson-Morley experiments of 1881 and 1887, Oliver Joseph Lodge proves that the ether does not exist and that all motion is relative, which would lead to Einstein’s special theory of relativity.
• 1893: Ernst Mach states Mach’s principle (the local motion of a rotating reference frame is determined by the large scale distribution of matter); first constructive attack on the idea of Newtonian absolute space.
• 1894: Lord Rayleigh and William Ramsay discover argon (element 18) by spectroscopically analyzing the gas left over after nitrogen and oxygen are removed from air.
• 1895: Discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet (later identified as photons) because it is strongly absorbed by air, by the German physicist Victor Schumann.
• 1895: Pierre Curie demonstrates experimentally that the susceptibility of a paramagnetic substance to an external magnetic field varies inversely with temperature.
• 1895: C. V. Boys calculated the mean density of the Earth as 5.527 times the density of water. Boys published a measurement of the gravitational constant G that improved upon the accuracy achieved by Cavendish. Boys’ method relied on the same theory as Cavendish’s, but used two masses suspended at one height and two nearby masses suspended at a different height, to minimize the unwanted interaction between opposite masses.
• 1895: Braun invents the oscilloscope.
• 1895: Dewar is the first to produce liquid hydrogen.
• November 1895: Wilhelm Röntgen discovers X-rays. By December, he had used them to take pictures of human bones, and within a year their practical value was well understood. The rapid spread of the use of X-rays throughout the world foreshadowed the way scientists, engineers, and inventors would turn fundamental discoveries into technological applications in the coming century. But no one knew where X-rays came from. Lord Kelvin declared them a hoax.
• 1895: The President of the Royal Society of England, Lord Kelvin, declares, “Heavier than air flying machines are impossible.” In 1896 he refused an invitation to join the Aeronautical Society, writing that “I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of.” And in a 1902 newspaper interview he predicted that “No balloon and no aeroplane will ever be practically successful.”
• 1895: Carl von Linde succeeded in liquefying air by first compressing it and then letting it expand rapidly, thereby cooling it. He then obtained oxygen and nitrogen from the liquid air by slow warming.
• February-March 1896: Henri Becquerel wrapped a photographic plate in a double thickness of black paper, coated the paper with bisulphate of uranium and potassium, and exposed the whole thing to the sun for several hours. He thus discovered that certain kinds of matter emit radiation (what he called “uranic rays”) on their own accord.
• 1896: Alfred Perot and Charles Fabry invent the interferometer.
• 1896: Pieter Zeeman studies the splitting of sodium D lines when sodium is held in a flame between strong magnetic poles.
• June 1896: Wien publishes a distribution law for blackbody radiation that is in agreement with the available data.
• April 1897: Electrons are discovered by J. J. Thomson.
• 1897: Balmer publishes his final paper, containing equations to describe the spectral lines of helium and lithium.
• 1898: Polish-born Marie Curie identifies the element polonium, which spontaneously changes into lead upon giving off radiation. This discovery shattered the belief inherited from the Greeks that the elements are immutable and their atoms indestructible. The same year, she discovered radium.
• 1898: Henri Poincaré states that simultaneity is relative.
• 1898: William Ramsay and Morris Travers discover neon (element 10), and negatively charged beta particles.
• 1898: Boltzmann wrote that hopefully “when the theory of gases is again revived, not too much will have to be rediscovered.”
• 1898: The magnetic recording was demonstrated in principle by Valdemar Poulsen in his telegraphone. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head (which may be the same as the recording head) can then pick up the changes in the magnetic field from the tape and convert them into an electrical signal.
• 1899: Edouard Eugene Desire Branly demonstrated the coherer, an invention of his that enabled radio waves from a distant transmitter to be detected.
• 1899: Ernest Rutherford discovered the alpha and beta particles emitted by uranium.
• 1899: Phillip Lenard showed that cathode rays (electrons) can be produced by light shining onto a metal surface in a vacuum.

The Age of Quantum Mechanics Begins

• 1900: Max Planck’s formula for the energy distribution in the spectrum of heat radiation, which demonstrated that the energy is not continuous but quantized.
• 1900: Paul Villard discovered the Gamma ray, a high-energy photon, in uranium decay.
• 1900: Lord Kelvin gave a lecture titled “Nineteenth-Century Clouds over the Dynamical Theory of Heat and Light”. The two “dark clouds” he was alluding to were the unsatisfactory explanations that the physics of the time could give for two phenomena: the Michelson–Morley experiment and black body radiation. Two major physical theories were developed during the twentieth century starting from these issues: for the former, the Theory of relativity; for the second, quantum mechanics.
• 1901: Building off of Branly’s work, Guglielmo Marconi made the first transatlantic radio transmission.
• 1902: Following Marconi’s transmission, Oliver Heaviside and Arthur Edwin Kennelly independently propose that a layer of electrically charged particles must exist in the atmosphere in order to reflect radio waves back to the ground.
• 1902: James Jeans finds the length scale required for gravitational perturbations to grow in a static nearly homogeneous medium.
• 1903: Crookes invents the spinthariscope, an alpha-ray detector.
• 1903: Paul Langevin publishes a theory for the recombination of positive and negative ions at different pressures.
• 1904: Charles Glover Barkla found that, unlike the low atomic mass elements, the heavy elements produced secondary radiation of a longer wavelength than that of the primary X-ray beam.
• 1904: Otto Hahn discovers radiothorium.
• 1904: Henri Poincaré presents the principle of relativity for electromagnetism.
• June 1905: Albert Einstein, then a Bern patent clerk, publishes a paper on the existence of light quanta and the photoelectric effect.
• July 1905: Einstein publishes a paper explaining Brownian motion.
• September 1905: Einstein argued in a paper called “On the Electrodynamics of Moving Bodies” that the speed of light was a constant in all inertial reference frames and that electromagnetic laws should remain valid independent of reference frame—assertions which rendered the ether “superfluous” to physical theory, and that held that observations of time and length varied relative to how the observer was moving with respect to the object being measured (what came to be called the “special theory of relativity”). It also followed that mass and energy were interchangeable quantities according to the equation E=mc2.
• 1906: Charles Barkla demonstrates polarization by double scattering, but many people are not convinced, since such experiments could also be explained in terms of spinning particles.
• December 1906: Einstein publishes a paper on the quantum theory of specific heat.
• 1907: Hahn discovers mesothorium, a radioactive isotope of radium.
• 1907: Einstein introduces the principle of equivalence of gravitation and inertia and uses it to predict the gravitational redshift.
• 1907: Pierre Weiss developed the domain theory of ferromagnetism. Weiss believed ferromagnetism might be the result of an unusually strong interaction between the individual atomic magnets, which in some way made them all point in the same direction.
• 1908: Hans Wilhelm Geiger develops a device that counts alpha particles.
• 1908: Dutch experimental physicist Heike Kamerlingh-Onnes succeeds in liquefying helium.
• September 21, 1908: Einstein’s former teacher Hermann Minkowski addresses the 80th Assembly of German Natural Scientists and Physicians and says, “The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.”
• September 1909: Einstein announces that “the next stage in the development of theoretical physics will bring us a theory of light that may be conceived of as a sort of fusion of the wave and of the emission theory of light.”
• 1910: Theordor Wulf, investigating atmospheric ionization using an electroscope on top of the Eiffel Tower, found that ionization at 300m above the ground was greater than at ground level, from which he concluded that the ionization was caused by extraterrestrial rays.
• 1911: Onnes cooled liquid mercury down to -270 degrees Celsius (4.2 degrees Kelvin) and discovered that resistance to electric current vanished entirely, creating a superconductor.
• March 1911: Ernest Rutherford established that the bulk of mass in atoms are concentrated in positively charged nuclei with orbiting electrons, based on scattering observed by Hans Geiger and Ernest Marsden, which was a theoretically unstable configuration.
• 1911: Frederick Alexander Lindemann constructs a special calorimeter and measures specific heats at very low temperatures.
• 1911: Einstein told the participants of the first Solvay Congress: “I insist on the provisional character of this concept (light quantum), which does not seem reconcilable with the experimentally verified consequences of the wave theory.”
• 1912: Victor Hess discovers that the ionization of air increases with altitude indicating the existence of cosmic radiation.
• 1912: Peter Debye derives the T-cubed law for the low temperature heat capacity of a nonmetallic solid.
• 1913: Frederick Soddy suggested the idea of isotopes. He coined the term “isotope” from the Greek for “same place” in 1914. Atoms with different weights could belong in the same place on the periodic table of the elements. The word was actually suggested to Soddy by Margaret Todd, a Scottish physician to whom he was distantly related by marriage, during a conversation in which he explained his ideas to her.
• July 1913: Bohr publishes his first paper on the quantum theory model of the atom.
• 1913: William Henry Bragg constructs the first X-ray spectrometer.
• 1913: Fabry demonstrates that ozone is plentiful in the upper atmosphere and is responsible for keeping out ultraviolet radiation.
• 1913: Dutch physicist Willem de Sitter suggests that fast-moving binary stars could be used to measure the effect of a moving source on the speed of light.
• 1914: Fabry and Henri Buisson used the interferometer to confirm the Doppler effect for light.
• 1914: Finnish physicist Gunnar Nordstrom found that all you had to do to unify gravity with electromagnetism was increase the dimensions of space by one.
• April 1914: The Franck-Hertz experiment confirms Bohr’s concept of quantum jumps and atomic energy levels.
• 1915: William Napier Shaw invents the tephigram, one of four thermodynamic diagrams commonly used in weather analysis and forecasting.
• 1915: Einstein writes to mathematician David Hilbert: “I have often tortured my mind in order to bridge the gap between gravitation and electromagnetism.”
• November 1915: Einstein completes his theory of general relativity in Berlin and presents it to the Prussian Academy on November 25. The new theory of curved space and warped time perfectly matches Mercury’s strange motions that baffled Urbain Le Verrier as far back as 1855.
• 1915: Karl Schwarzschild publishes the Schwarzschild metric about a month after Einstein published his general theory of relativity. This was the first solution to the Einstein field equations other than the trivial flat space solution.
• 1916: Einstein shows that the field equations of general relativity admit wavelike solutions.
• January 1916: To account for the Zeeman effect (1896), i.e. that atomic absorption or emission spectral lines change when the light is first shone through a magnetic field, Arnold Sommerfeld suggested there might be “elliptical orbits” in atoms in addition to Bohr’s spherical orbits.
• 1917: Honda and Takei discovered the coercive force of tungsten steel could be vastly increased by added cobalt.
• 1918: Protactinium is discovered.
• 1918: J. Lense and Hans Thirring find the gravitomagnetic precession of gyroscopes in the equations of general relativity.
• April 1919: Einstein wrote to Theodor Kaluza, “The idea of achieving [a unified theory] by a five-dimensional cylinder had never occurred to me… At first glance I like your idea enormously.”
• May 29, 1919: When the bending of starlight by the Sun, as predicted by Einstein, was observed during a solar eclipse by Arthur Stanley Eddington from Principe Island off the west coast of Africa, Einstein instantly became an international media star (after the findings were presented on November 6 at the Royal Academy). The curvature of spacetime, while not fully comprehensible to most people, nevertheless seemed to be such a profound insight into the structure of the universe that it caught the imagination of a wide public. Since then, General Relativity has been confirmed by numerous observations, and remains in place as the correct theory of gravity.
• 1919: Francis Aston invents an electromagnetic separator (the mass spectrograph), in which a beam of ions is deflected by electric and magnetic fields so that ions of the same mass are brought to a focus at the same point, enabling the masses of the ions in the beam to be determined. This lead to the discovery of isotopes.
• 1919: Rutherford explained the transmutation of elements from experiments in which he bombarded nitrogen with alpha particles. This same year, he discovers the proton.
• 1919: Heinrich Georg Barkhausen discovered the Barkhausen effect, which provided evidence for the magnetic domain theory of ferromagnetism. When the magnetic field through a piece of ferromagnetic material like iron is changing, the magnetization of the material changes in a series of tiny discontinuous jumps, which can be heard as a series of clicks in a loudspeaker attached to a coil of wire around the iron. It was later determined that these jumps were caused by the movement of the magnetic domains in the iron, as the domain walls snap past defects in the crystal lattice. The energy lost in these dissipative events is responsible for the shape of the hysteresis curve of iron and other ferromagnets. This effect is widely used in research, and physics education as a simple experiment to demonstrate the reality of magnetic domains.
• March 1920: Sommerfeld introduces a fourth quantum number.
• 1920: Michelson announces the size of the giant star Betelgeuse, the first star (besides the Sun) to be measured.
• 1921: Theodor Kaluza demonstrates that a five-dimensional version of Einstein’s equations unifies gravitation and electromagnetism.
• September 30, 1921: Einstein writes to E. Zschimmer, “Now to the term ‘relativity theory.’ I admit that it is unfortunate, and has given occasion to philosophical misunderstandings.”
• 1922: Russian physicist Alexander Friedmann proposes expanding universe.
• 1922: Louis De Broglie was able to derive Planck’s formula E=hv using the particle theory of light. (E=energy, h=Planck’s constant and v=frequency of the radiation)
• May 1923: Arthur Compton publishes a paper on the Compton effect, in which X-rays are scattered on passing through matter and emerge with a longer wavelength. This paper is said to be irrefutable evidence of Einstein’s 1905 light-quanta hypothesis.
• July 1923: Pauli writes a letter to Sommerfeld saying, “The theory… with atoms having more than one electron, it is such a great misery.”
• September 1923: De Broglie links waves with electrons as he extends wave-particle duality to incorporate matter. He uses Einstein’s mass-energy equation and Planck’s quantum theory to achieve an expression describing the wave nature of a particle. He discovered that electrons do not occupy orbits but exist as standing waves around the nucleus. (He dared to ask, if light can behave as a wave, why not particles?)
• 1923: The Compton effect was observed by Arthur Holly Compton at Washington University in St. Louis and further verified by his graduate student Y. H. Woo in the years following. Compton scattering is a type of scattering that X-rays and gamma rays (both photons with different energy ranges) undergo in matter. The inelastic scattering of photons in matter results in a decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, called the Compton effect.
• 1924: Lord Patrick Maynard Stuart Blackett succeeds in obtaining the first photographs of an atomic transmutation, which was of nitrogen into an oxygen isotope.
• 1924: Max Born coins the term “quantum mechanics”.
• 1924: Edward Appleton finds the charged layer of atmosphere proposed by Heaviside and Kennelly (today called the ionosphere) at a height of 100km).
• 1924: Einstein says “there are therefore now two theories of light, both indispensable… without any logical connection.”
• 1925: Stellar structure understood
• 1925: Robert Andrews Millikan coins the term “cosmic rays”.
• January 1925: The Wolfgang Pauli exclusion principle is announced, which says that two fermions (particles) cannot occupy the same quantum state.
• May 1925: Pauli writes to Kronig saying that “physics at the moment is again very muddled.”
• 1925: Ernst Ising presents the solution to the one-dimensional Ising model.
• September 1925: Heisenberg publishes his first paper on matrix mechanics, “On a Quantum-Theoretical Reinterpretation of Kinematics and Mechanical Relations”.
• October 1925: Samuel Goudsmit and George Uhlenbeck propose the concept of quantum spin.
• 1926: Michelson measures the speed of light to be 299,796 km/s (with the actual speed being 299,792.5).
• 1926: George Uhlenbeck first hears of Oskar Klein’s idea and later remarks, “I felt a kind of ecstasy! Now one understands the world.”
• 1926: Gilbert Lewis coins the word “photon”.
• June 1926: Wien writes to Schrodinger about the “morass of integral and half-integral quantum discontinuities and the arbitrary use of the classical theory.”
• 1926: W. Wessel writes, “The question of a possible magnetism of atomic nuclei has been raised several times, but as far as we know, has never been discussed in detail.”
• January 1927: Clinton Davisson and Lester Germer study how a beam of electrons interact with a crystal made of nickel. They were surprised to see that electrons behave like waves, diffracted by the crystal lattices.
• 1927: Big Bang proposed by Roman Catholic priest Georges Lemaitre (though he did not use the term). His reasoning was simple: if you trace the universe backwards in history, it would get smaller and smaller. The “big bang” is the point of creation.
• May 1927: Werner Heisenberg’s “uncertainty principle” (indicating the impossibility of precisely and simultaneously measuring position and momentum) and the “Copenhagen interpretation” of quantum mechanics (named after Bohr’s home city) continued to deny the possibility of fundamental causality, though opponents such as Einstein would assert that “God does not play dice with the universe”.
• 1928: Antimatter predicted
• 1928: Paul Adrien Maurice Dirac formulates the relativistic theory of the electron, and postulated the existence of positrons as a consequence of the Dirac equation.
• 1928: Geiger and Walther Muller develop the Geiger Counter.
• 1928: Eugen Goldstein publishes a paper that explains when a discharge tube of nitrogen and hydrogen is discharged, a trace of ammonia is left behind. Later scientists would wonder if life started in this way.
• 1928: Felix Bloch applies quantum mechanics to electrons in crystal lattices, establishing the quantum theory of solids.
• 1929: Astronomer Edwin Hubble confirms the expansion of universe by looking through the 100-inch Hooker telescope at the Mount Wilson Observatory in California. He determined that the dimmer a galaxy was, the more its light was redshifted and thus moving away from Earth.
• 1929: Paul Adrien Maurice Dirac and Werner Karl Heisenberg develop the quantum theory of ferromagnetism.
• 1929: Sir Arthur Eddington’s book The Nature of the Physical World is published. In it, he says, “No familiar conceptions can be woven around the electron.” Our best description of the atom boils down to “something unknown is doing we don’t know what.”
• 1930: Nels Edlefsen, a student of Ernest Lawrence, makes the first cyclotron.
• 1930: Julius Robert Oppenheimer writes a paper on the “Relativistic Theory of the Photoelectric Effect”, in which, based on empirical evidence, he disagreed with Dirac’s assertion that the states of the hydrogen atom must have identical energy states.
• 1930: Wolfgang Pauli postulated the neutrino to explain the energy spectrum of beta decays.
• 1931: Lemaitre gives a seminar at Caltech where he explains his model universe to Einstein and Hubble.
• 1931: T. Mishima in Japan discovered that an alloy of iron, nickel, and aluminum had a coercivity of 400 oersted, double that of the best magnet steels of the time.
• 1932: The neutron is discovered by James Chadwick, after its existence had been suspected by Rutherford as early as 1920.
• 1932: Carl David Anderson reported that he had found positively charged particles that occurred as abundantly as did negatively charged particles, and that in many cases several negative and positive particles were simultaneously projected from the same center. This particle is today called the positron or antielectron.
• 1932: Louis Eugène Félix Neel discovers antiferromagnetism.
• 1932: John Cockcroft and Ernest Walton bombarded lithium with high energy neutrons, electrons and protons and succeeded in transmuting it into helium and other chemical elements. This was one of the earliest experiments to change the atomic nucleus of one element to a different nucleus by artificial means. This feat was popularly – if somewhat inaccurately – known as splitting the atom.
• 1933: While examining the Coma galaxy cluster, Fritz Zwicky was the first to use the virial theorem to infer the existence of unseen matter, what is now called dark matter. He was able to infer the average mass of galaxies within the cluster, and obtained a value about 160 times greater than expected from their luminosity, and proposed that most of the matter was dark.
• 1933: Edwin Howard Armstrong, working with Pupin, developed and patented a method of radio broadcasting in which the transmitted signal is made to modulate the frequency of the carrier wave over a wide waveband. This method, called frequency modulation (FM), is unaffected by static and is capable of high-fidelity sound reproduction.
• 1933: Lise Meitner uses a Wilson cloud chamber to photograph positron production by gamma radiation.
• 1933: Walter Meissner, F. Heidenreich and Robert Ochsenfeld discover perfect superconducting diamagnetism. A metal that becomes a superconductor actually expels the flux if the temperature is lowered through the transition value while the specimen is in a magnetic field.
• June 1933: Einstein gives a lecture at Oxford University, saying, “I am convinced that we can discover by means of purely mathematical constructions… the key to understanding natural phenomena. Experience may suggest the appropriate mathematical concepts, but they most certainly cannot be deduced from it. The creative principle lies in mathematics… In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.”
• 1934: The Joliet-Curies discover artificial radioactivity using alpha-particle bombardment.
• 1934: Enrico Fermi discovers that uranium is among the elements in which neutron bombardment induces transformations.
• 1935: Homi Jehangir Bhabha becomes the first person to determine the cross-section (and thus the probability) of electrons scattering positrons.
• 1935: Erwin Schroedinger presents his infamous “Schroedinger’s cat” experiment in the journal Naturwissenschaften.
• 1935: Hideki Yukawa of Osaka University predicted the existence of mesons as the carrier particles of the strong nuclear force, the force that holds neutrons and protons together in a nucleus in spite of the positive charge that would blow the nucleus apart from the electric force.
• 1935: Matvei Petrovich writes the first ever doctoral dissertation on quantum gravity.
• May 1935: Einstein, Podolsky and Rosen publish the paper, “Can Quantum Mechanical Description of Physical Reality Be Considered Complete?”
• 1935: Russian physicists Lev Landau and Evgeny Lifshitz pioneered the mathematical study of domains in ferromagnetic crystals.
• 1936: The muon (mu-meson, originally the mesotron) is discovered by Carl Anderson. While studying tracks in a cloud chamber, he noticed an unusual track that seemed to have been made by a particle intermediate in mass between a proton and an electron.
• 1936: Kenneth Tompkins Bainbridge invents a double-focusing spectroscopy machine.
• 1936: George Gamow and Edward Teller produced the Gamow-Teller selection rule for beta decay.
• 1936: Petrovich writes in a paper that “the elimination of the logical inconsistencies [requires] rejection of our ordinary concepts of space and time, modifying them by some much deeper and nonevident concepts.”
• 1937: Pyotr Leonidovich Kapitsa and John Frank Allen discover superfluidity, a state of matter, like solid, liquid or gas, in which the viscosity of a fluid vanishes, while thermal conductivity becomes infinite.
• 1937: Fritz Zwicky states that galaxies could act as gravitational lenses.
• 1937: Einstein, Leopold Infeld, and Banesh Hoffmann show that the geodesic equations of general relativity can be deduced from its field equations.
• 1937: Muon (or mu lepton) discovered by Seth Neddermeyer, Carl D. Anderson, J.C. Street, and E.C. Stevenson, using cloud chamber measurements of cosmic rays. (It was mistaken for the pion until 1947.)
• 1938: Hans Albrecht Berthe showed that nuclear reactions could power the Sun.
• 1939: Hannes Alfven proposed a theory to explain aurorae and magnetic storms, a theory that greatly influenced later ideas about the Earth’s magnetosphere.
• June 28, 1939: Uranium fission is discovered, and Niels Bohr and John Wheeler write an article for The Physical Review. As soon as nuclear fission was discovered in Europe, it became apparent that if a way could be found to release its energy in a bomb, the course of the war would be altered. In America a number of physicists, many of European origin, worried that Hitler might acquire such a weapon and persuaded the normally pacifistic Albert Einstein to warn President Franklin D. Roosevelt.
• July 10, 1939: Oppenheimer and his student Hartland Snyder produced the paper “On Continued Gravitational Contraction”, which predicted the existence of what we today call black holes. It was published September 1 in The Physical Review.
• August 2, 1939: In an urgent letter to FDR, Einstein explained the danger of nuclear fission by writing: “It is conceivable … that extremely powerful bombs of a new type may thus be constructed.” Einstein’s letter did not have an immediate effect, but eventually helped to persuade the United States to begin the monumental task of building an atom bomb.
• 1940: Edwin McMillan and Philip Abelson discover neptunium (element 93).
• 1941: Lev Davidovich Landau explains superfluidity.
• 1942: Hannes Alfven postulated that a form of electromagnetic wave (the magnetohydrodynamic wave) would propagate through plasma.
• December 1942: Enrico Fermi and his team at the University of Chicago achieve the first controlled nuclear chain reaction.
• 1944: Schrodinger publishes What Is Life? and argues that the fundamental molecules of life could be understood in terms of the laws of physics.
• 1944: Lars Onsager publishes the exact solution to the theory of magnetism in 2D Ising model.
• 1945: George Gamow writes, “Instead of a rather large number of ‘indivisible atoms’ of classical physics, we are now left with only three essentially different entities: nucleons, electrons, and neutrinos. And in spite of the greatest desire and effort to reduce everything to its simplest form, one cannot possibly reduce something to nothing. Thus it seems that we have actually hit the bottom in our search for the basic elements from which matter is formed.”
• 1946: Martin Ryle and Vonberg build the first two-element astronomical radio interferometer.
• 1947: The pion (pi-meson) is discovered by Cecil Frank Powell, matching the particle predicted by Hideki Yukawa in 1935.
• 1947: Dennis Gabor realizes that a beam of coherent light reflected from an object contains information on the shape of the object.
• 1947: George Dixon Rochester and Clifford Charles Butler discovered the Kaon (or K meson), the first strange particle.
• 1947: Lambda baryon discovered during a study of cosmic ray interactions.
• Supermalloy was discovered. Supermalloy is an alloy composed of nickel (79%), molybdenum (5%), and iron. It is a magnetically soft material and has an extremely high magnetic permeability and a low coercivity. Supermalloy is used in manufacturing components for radio engineering, telephony, and telemechanics instruments.
• 1948: Quantum electrodynamics
• April 1, 1948: George Gamow produced an important cosmogony paper with his student Ralph Alpher, which was published as “The Origin of Chemical Elements” in Physical Review. This paper became known as the Alpher-Bethe-Gamow theory and predicted cosmic background radiation.
• 1948: Claude Elwood Shannon establishes information theory, a branch of applied mathematics and electrical engineering involving the quantification of information.
• March 28, 1949: Fred Hoyle coins the term “big bang” on the BBC Third Programme radio show. Ironically, it was not a theory he supported, and said an explosion was an undignified way for the world to begin, rather like “a party girl jumping out of a cake.”
• 1949: Herbert Friedman detects evidence for extrasolar X-rays.
• November 22, 1951: Pope Pius XII declares the idea of the big bang compatible with the Catholic concept of creation. (Pius XII also recognized the theory of evolution.)
• 1952: Hoyle predicts that the sum of the energies of a beryllium nucleus and a helium nucleus must be almost exactly the energy of a certain quantum state of the isotope of carbon formed, a situation called a resonance, which greatly increases the rate of a nuclear reaction.
• 1952: Alexei Alexeyevich Abrikosov discovered the way in which magnetic flux can penetrate a superconductor. The phenomenon is known as type-II superconductivity, and the accompanying arrangement of magnetic flux lines is called the Abrikosov vortex lattice.
• David Bohm of Birkbeck College introduced the idea of spin measurements in a new version of the EPR thought experiment.
• 1953: The Urey-Miller experiment occurred, where a primitive “soup” of methane, ammonia, hydrogen and water were zapped to produce organic compounds.
• 1953: James Watson and Francis Crick publish the double helix model for the structure of DNA.
• 1953: Charles Townes invents the first working model of the maser (Microwave Amplification by Stimulated Emission of Radiation).
• 1955: Percy Williams Bridgman synthesizes a diamond.
• 1955: Emilio Segre and Owen Chamberlain discover the antiproton (or negative proton or negatron) by using a large magnet. An antiproton consists of two up antiquarks and one down antiquark (uud). The properties of the antiproton that have been measured all match the corresponding properties of the proton, with the exception that the antiproton has opposite electric charge and magnetic moment than the proton.
• 1955: The 100th element, fermium, is discovered and named after Enrico Fermi, who died in November of 1954.
• 1956: Electron neutrino discovered by Clyde Cowan and Frederick Reines (proposed by Wolfgang Pauli in 1931 to explain the apparent violation of energy conservation in beta decay). At the time it was simply referred to as neutrino since there was only one known neutrino. They performed their experiment next to a nuclear reactor at Savannah River, South Carolina.
• 1956: R. Hanbury-Brown and R.Q. Twiss complete the correlation interferometer.
• April 1956: T. D. Lee proposes “parity doubling”.
• 1956: Leon N. Cooper shows that for a sufficiently strong and attractive lattice-mediated force, there is indeed a strong correlation between pairs of electrons of opposite spins; but it is essentially a correlation in momentum “space” rather than in position.
• 1957: John Bardeen, Leon Cooper, and Robert Schrieffer develop the BCS theory of superconductivity.
• 1957: Bruno Pontecorvo postulated the flavor oscillation.
• 1957: John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity.
• 1957: Aleksandr Solomonovich Kompaneets derives his Compton scattering Fokker–Planck equation.
• 1957: Ryogo Kubo derives the first of the Green-Kubo relations for linear transport coefficients.
• 1957: Edwin T. Jaynes gives MaxEnt interpretation of thermodynamics from information theory.
• July 1957: Hugh Everett III proposes the many-worlds interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real—each representing an actual “world” (or “universe”).
• 1959: Philip Warren Anderson predicts localization in disordered systems.
• May 11, 1959: Eugene Wigner writes, “The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. We should be grateful for it and hope that it will remain valid in future research and that it will extend, for better or for worse, to our pleasure, even though perhaps also to our bafflement, to wide branches of learning.”
• 1960: Theodore Harold Maiman constructs the first working laser (Light Amplification by Stimulated Emission of Radiation).
• 1960: Robert Pound and Glen Rebka test the gravitational redshift predicted by the equivalence principle to approximately 1%. They studied gamma rays emitted from radioactive iron. This is now known simply as the “Pound–Rebka experiment”.
• 1961: Robert Dicke argues that the universe must be about 10 billion years old. He reasons it would take that long for the carbon to scatter, but too much longer and the fuel in the stars would burn out. (Today we estimate the universe at about 13.7 billion years old).
• 1961: Ali Javan makes the first continuous-beam laser at the Bell Telephone Laboratories.
• 1961: Clauss Jönsson of the University of Tübingen performed the double-slit experiment with electrons, whereas previous scientists had only used light. In 2002, Jönsson’s double-slit experiment was voted “the most beautiful experiment” by readers of Physics World.
• 1962: Fang Lizhi publishes the first paper on the line width of laser emission.
• 1962: Muon neutrino found by Leon M. Lederman, Melvin Schwartz and Jack Steinberger.
• 1962: Riccardo Giacconi, Herbert Gursky, F. Paolini, and Bruno Rossi formally discover the X-ray background.
• 1962: Dicke, Peter Roll, and R. Krotkov use a torsion fiber balance to test the weak equivalence principle to 2 parts in 100 billion.
• 1962: Richard Feynman attends a meeting in Warsaw and decides that the field of gravity “is not an active one”.

Age of the Standard Model Begins

• February 5, 1963: Astronomers Maarten Schmidt and Jesse Greenstein at Caltech made a discovery. Using the famous 200-inch reflector telescope at Mt Palomar, Schmidt identified a visible object corresponding to a radio source, known as 3C 273, and also studied its spectrum. While its star-like appearance suggested it was relatively nearby, the spectrum of 3C 273 proved to have what was at the time a high redshift of 0.158, showing that it lay far beyond the Milky Way, and thus possessed an extraordinarily high luminosity. Schmidt termed 3C 273 a “quasi-stellar” object or quasar; thousands have since been identified.
• 1963: Murray Gell-Mann and George Zweig propose the quark/aces model.
• 1964: Dicke performs an experiment using a sensitive balance and laser beams to measure the possible difference between the gravitational pull of the Sun on objects made of different materials. His experiments put an upper limit of 1 part in a trillion on such a difference.
• 1964: The omega-minus particle is discovered.
• 1964: Irwin Shapiro predicts a gravitational time delay of radiation travel as a test of general relativity.
• 1964: Xi baryon discovery at Brookhaven National Laboratory.
• 1964: Peter Higgs considers the breaking of local phase symmetry.
• November 1964: John Stewart Bell shows that all local hidden variable theories must satisfy Bell’s inequality.
• 1964: Val Fitch and James Cronin observe CP violation by the weak force in the decay of K mesons.
• 1964: Arno Penzias and Robert Wilson encountered radio noise which they could not explain. It was far less energetic than the radiation given off by the Milky Way, and it was isotropic, so they assumed their instrument was subject to interference by terrestrial sources. They tried, and then rejected, the hypothesis that the radio noise emanated from New York City. An examination of the microwave horn antenna showed it was full of pigeon droppings (which Penzias described as “white dielectric material”). After the pair removed the guano buildup, and the pigeons were shot (each physicist says the other ordered the deed), the noise remained. Having rejected all sources of interference, the pair published a paper announcing their findings.
• 1965: Robert Dicke determines the findings of Penzias and Wilson to be cosmic microwave background radiation (CMBR), supporting the idea of the expanding universe.
• 1965: Joseph Weber puts the first Weber bar gravitational wave detector into operation.
• 1965: Richard Feynman writes, “There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper, a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics.”
• 1966: Georgiy Zatsepin, Vadim Kuzmin and Kenneth Greisen make the GZK prediction, proposing a theoretical upper limit on the energy of cosmic rays from distant sources.
• November 28, 1967: Pulsars (neutron stars) are discovered by Jocelyn Bell Burnell and Antony Hewish, and scientists briefly (and falsely) believe they are receiving signals from an alien civilization.
• 1967: Pakistani Abdus Salam and American Steven Weinberg independently proposed theories in which electromagnetism was unified with the weak force. This is called the electroweak theory.
• 1967: Bruno Pontecorvo postulated the Neutrino oscillation.
• 1968: Experimental evidence for “quarks” (a name taken from James Joyce’s Finnegan’s Wake by Murray Gell-Mann) found at the Stanford Linear Accelerator Center.
• 1968: Irwin Shapiro presents the first detection of the Shapiro delay.
• 1968: Kenneth Nordtvedt studies a possible violation of the weak equivalence principle for self-gravitating bodies and proposes a new test of the weak equivalence principle based on observing the relative motion of the Earth and Moon in the Sun’s gravitational field.
• 1968: Gabriele Veneziano saw an interesting pattern in the data and described the pattern by writing down a formula that described the probabilities for two particles to scatter from each other at different angles.
• 1969: Partons (internal constituents of hadrons) observed in deep inelastic scattering experiments between protons and electrons at SLAC; this was eventually associated with the quark model (predicted by Murray Gell-Mann and George Zweig in 1964) and thus constitutes the discovery of the up quark, down quark, and strange quark.
• 1969: John Clauser, Michael Horne, Abner Shimony and Richard Holt propose a polarization correlation test of Bell’s inequality.
• 1970: Sheldon Glashow, John Iliopoulos, and Luciano Maiani propose the charm quark.
• 1970: Pierre Ramond found a way to alter the equations describing a string, so that it would have fermions… and thus he discovered supersymmetry.
• October 1971: An experiment is carried out with a clock on an airplane going westward while compared to a clock on the ground. The clock in the airplane ran faster, meaning (in theory) you could extend your life by always flying eastward, though it would only be about 180 billionths of a second per rotation, and perhaps less is taking gravity into account.
• 1971: Dutch theorist Gerard ‘t Hooft shows that the Glashow-Salam-Weinberg electroweak model can be renormalized, the Yang-Mills theories were completely sensible as quantum theories.
• 1971: Evgeny Likhtman and Yuri Golfand develop a theory of supersymmetry, whereby you could replace a boson with a fermion and still get a stable world.
• 1972: Douglas Osheroff, Robert C. Richardson, and David Lee discover that helium-3 can become a superfluid.
• 1972: Stuart Freedman and John Clauser perform the first polarization correlation test of Bell’s inequality.
• 1972: Andrei Neveu and Joel Scherk found that the superstring had states of vibrations corresponding to gauge bosons, including the photon.
• November 2, 1972: Israeli graduate student Jacob Bekenstein suggests that black holes have an entropy proportional to their surface area.
• 1973: David Politzer proposes the asymptotic freedom of quarks.
• 1973: David Gross, working with his first graduate student, Frank Wilczek, at Princeton University, discovered asymptotic freedom, which holds that the closer quarks are to each other, the less the strong interaction (or color charge) between them; when quarks are in extreme proximity, the nuclear force between them is so weak that they behave almost as free particles. Asymptotic freedom, independently discovered by David Politzer, was important for the development of quantum chromodynamics.
• 1974: the Wess–Zumino model became the first known example of an interacting four-dimensional quantum field theory with supersymmetry, at least in the Western world. Julius Wess and Bruno Zumino studied, using modern terminology, dynamics of a single chiral superfield (composed of a complex scalar and a spinor fermion) whose cubic superpotential leads to a renormalizable theory.
• January 17, 1974: Stephen Hawking submits a paper to the journal Nature called “Black Hole Explosions?”
• February 1974: Hawking presents a paper at the Rutherford-Appleton Laboratory in Oxford, suggesting that black holes will radiate particles with a black-body spectrum which can cause black hole evaporation. The moderator, mathematician John Taylor, called it “absolute rubbish”.
• March 5, 1974: John Taylor and Paul Davies submit a paper to Nature called “Do Black Holes Really Explode?”, arguing against Hawking.
• 1974: Joel Scherk and John H. Schwarz found that some of the massless particles predicted by string theory could actually be gravitons. String theory could then unify gravity with the other three forces.
• December 10, 1974: Hawking bets a one year subscription of “Penthouse” with Kip Thorne that Cygnus X-1 was not a black hole. The idea was that if Hawking won, he would lose credibility as a proponent of black holes, but still had Thorne’s wager to comfort him (a four-year subscription to “Private Eye”). If he lost, he would have to give Thorne the porn, but would be vindicated. It was a win-win for Hawking, who would later concede the bet.
• 1974: Burton Richter and Samuel Ting discovered the psi meson, a flavor-neutral meson consisting of a charm quark and a charm antiquark.
• 1974: Kenneth G. Wilson develops the “renormalization group” technique for treating phase transitions.
• 1974: Robert J. Buenker and Sigrid D. Peyerimhoff introduce the multireference configuration interaction method.
• 1974: Howard Georgi and Sheldon L. Glashow present a paper on the Grand Unified Theory (GUT). It begins, “We present a series of hypotheses and speculations leading inescapably to the conclusion… that all elementary particle forces (strong, weak and electromagnetic) are different manifestations of the same fundamental interaction involving a single coupling strength. Our hypotheses may be wrong and our speculations idle, but the uniqueness and simplicity of our scheme are reasons enough that it be taken seriously.”
• 1975: Tau lepton discovered by a group headed by Martin Perl.
• 1976: Robert Vessot and Martin Levine use a hydrogen maser clock on a Scout D rocket to test the gravitational redshift predicted by the equivalence principle to approximately 0.007%.
• 1976: Gravity Probe A experiment confirmed slowing the flow of time caused by gravity matching the predicted effects to an accuracy of about 70 parts per million.
• 1976: Sergio Ferrara, Daniel Z. Freedman, and Peter van Nieuwenhuizen discovered Supergravity at Stony Brook University in New York. It was initially proposed as a four-dimensional theory. The theory of supergravity generalizes Einstein’s theory of general relativity by incorporating the principles of supersymmetry.
• 1977: Martin Lewis Perl discovered the Tau lepton after a series of experiments.
• 1977: Upsilon particle (proposed by Kobayashi and Maskawa in 1973) discovered at Fermilab by Steve Herb, demonstrating the existence of the bottom quark (which weighs five times the mass of a proton).
• 1978: Dark matter found in galaxies
• 1979: Gluon observed indirectly in three jet events at the German Electron Synchrotron (DESY).
• 1979: Dennis Walsh, Robert Carswell, and Ray Weymann discover the gravitationally lensed quasar Q0957+561.
• 1979: Theory of cosmic inflation proposed by Alan Guth of MIT. The theory asserts that the universe went through a spurt of enormous growth extremely early in its life (in under one second), and it explains why the universe looks pretty much the same in every direction.
• 1980: Klaus von Klitzing discovers the Quantum Hall effect, a quantum-mechanical version of the Hall effect.
• 1981: Mordehai Milgrom proposes Modified Newtonian dynamics (MOND) as an alternative to the dark matter and galaxy rotation curve problems.
• 1981: An ancient dream came true when the outlines of individual atoms were revealed to the human eye for the first time. Scanning Tunneling Microscope (STM) The instrument that made this possible, called the Scanning Tunneling Microscope (STM), consists of a fine needle whose tip gently scans a surface the way a blind person’s fingertip might scan an unfamiliar face. The digitized contours are fed into a computer which organizes them into a picture resembling the underside of an egg carton: each bump represents a single atom. Synthetic color coding adds to the contrast and helps to identify atoms of different species. The resulting map of the invisible atomic landscape we inhabit is imbued with a haunting beauty.
• 1982: Horst L. Stoermer and Daniel C. Tsui discover the fractional Quantum Hall effect, a physical phenomenon in which the Hall conductance of 2D electrons shows precisely quantised plateaus at fractional values of e2 / h.
• 1982: Joseph Taylor and Joel Weisberg show that the rate of energy loss from the binary pulsar PSR B1913+16 agrees with that predicted by the general relativistic quadrupole formula to within 5%.
• 1982: The first millisecond pulsar, PSR B1937+21, was discovered by Backer et al. Spinning roughly 641 times a second, it remains the second swiftest-spinning millisecond pulsar of the approximately 180 that have been discovered.
• Summer 1982: Alain Aspect, J. Dalibard, and G. Roger perform a polarization correlation test of Bell’s inequality that rules out conspiratorial polarizer communication. Basically, this team from the University of Paris-South, set out to detect the underlying reality below the unreal world of the quantum.
• 1982: Lee Smolin published “On the Relationship Between Quantum and Thermal Fluctuations”, which he considers his best paper to this day.
• 1983: Robert B. Laughlin explains the fractional quantum Hall effect.
• 1983: W and Z particles are directly observed by Carlo Rubbia, Simon van der Meer and the CERN UA1 collaboration (predicted in detail by Sheldon Glashow, Abdus Salam, and Steven Weinberg).
• March 1983: John Gribbin reflects in New Scientist that “without quantum theory there would be no genetic engineering, no solid-state computers, no nuclear power stations (or bombs).”
• 1985: Heterotic string theory was first developed by David Gross, Jeffrey Harvey, Emil Martinec, and Ryan Rohm (the so-called Princeton String Quartet), in one of the key papers that fueled the first superstring revolution. A heterotic string is a peculiar mixture (or hybrid) of the bosonic string and the superstring. In their paper they wrote, “Although much work remains to be done there seem to be no insuperable obstacles to deriving all of known physics from the … heterotic string.”
• 1986: Johannes Georg Bednorz succeeded in inducing superconductivity in a lanthanum barium copper oxide (LaBaCuO, also known as LBCO); the oxide’s critical temperature (Tc) was 35 K, a full 12 K higher than the previous record. This discovery stimulated a great deal of additional research in high-temperature superconductivity on cuprate materials with structures similar to LBCO, soon leading to the discovery of compounds such as BSCCO (Tc 107K) and YBCO (Tc 92K).
• 1986: Andrew Strominger discovered a way to construct a vast number of additional supersymmetric string theories, as a huge number of string theories were apparently consistent.
• 1986: Abhay Ashtekar published a reformulation of general relativity making the equations much simpler.
• 1987: Steven Weinberg pointed out that the cosmological constant must be less than a certain value, otherwise the universe would have expanded too rapidly for galaxies to form.
• 1988: David Gross and Paul Mende show that when quantum mechanics is taken into account, continually increasing the energy of a string does not continually increase its ability to probe finer structures, in direct contrast with what happens for a point particle.
• 1989: D-branes were discovered by Dai, Robert Leigh and Joseph Polchinski, and independently by Petr Hořava.
• October 15, 1991: The Oh-My-God particle (a play on the nickname “God particle” for the Higgs boson) is observed over Dugway Proving Ground, Utah.
• April 1992: George Smoot announces the Cosmic Background Explorer (COBE) satellite had detected tiny temperature variations in the background radiation.
• 1992: Stanley Mandelstam published a paper that was believed to prove that superstring theories are finite to all orders of a certain approximation scheme.
• 1992: Lee Smolin published a paper proposing that string theory had to be regarded as a landscape of theories.
• May 1994: Miguel Alcubierre publishes “The Warp Drive: Hyper-fast travel within general relativity” (which appeared in the science journal Classical and Quantum Gravity). In this, he describes the Alcubierre drive, a theoretical means of traveling faster than light that does not violate the physical principle that nothing can locally travel faster than light.
• October 1994: Scientific American declares the big bang theory correct, implying that cosmologists clinging to the steady state model, such as Fred Hoyle and Jay Narlikar, should move on.
• March 1995: Edward Witten proposes M-Theory at a conference in Los Angeles, a unifying theory that would bring the various consistent string theories together. The catch was that he only proposed the idea, not how to get there. Such a theory would require 11 dimensions.
• 1995: Eric Allin Cornell, along with Carl E. Wieman, was able to synthesize the first Bose-Einstein condensate.
• 1995: Top quark discovered at Fermilab.
• 1995: Antihydrogen produced and measured by the Low Energy Antiproton Ring (LEAR) experiment at CERN.
• Fall 1995: Joseph Polchinski showed that a string theory, to be consistent, must include not only strings but surfaces of higher dimensions moving in the background space. Polchinski identified D-branes with black p-brane solutions of supergravity, a discovery that triggered the Second Superstring Revolution and led to both holographic and M-theory dualities.
• December 1997: Anton Zeilinger successfully discovers quantum teleportation.
• January 1998: Saul Perlmutter observes distant supernovae, revealing the universe is expanding at an accelerating rate, an effect that is not possible without some kind of repulsive force acting throughout space. Thus “dark energy” was discovered. By “dark” energy, what is meant is that it seems to differ from all forms of energy and matter previously known, in that it is not associated with any particles or waves. It is just there.
• 1998: Neutrino discovered to have mass, contrary to previous assumptions.
• 1999: M. Henny and others demonstrate the Fermionic Hanbury Brown and Twiss Experiment.
• 2000: Tau neutrino proved distinct from other neutrinos at Fermilab.
• 2000: Giovanni Ameliano-Camelia proposed doubly special relativity.
• 2001: The Microwave Anisotropy Probe (MAP) was launched, a satellite with much higher precision than COBE.
• 2003: Wilkinson Microwave Anisotropy Probe (WMAP) observations of Cosmic microwave background.
• 2005: At the Relativistic Heavy Ion Collider (RHIC) accelerator of Brookhaven National Laboratory they have created a quark-gluon liquid of very low viscosity, perhaps the quark-gluon plasma.
• 2007: End of Gravity Probe B experiment. Initial results confirmed the expected geodetic effect to an accuracy of about 1%.
• 2008: The Large Hadron Collider at CERN is scheduled to begin operation in this year. Its primary goal is to search for the Higgs boson, which has not yet been found.
• 2009: Petr Hořava proposes “Hořava gravity”, a theory of quantum gravity. It solves the problem of different concepts of time in quantum field theory and general relativity by treating the quantum concept as the more fundamental so that space and time are not equivalent (anisotropic). The relativistic concept of time with its Lorentz invariance emerges at large distances. The theory relies on the theory of foliations to produce its causal structure. It is related to topologically massive gravity and the Cotton tensor. It is a possible UV completion of general relativity. The novelty of this approach, compared to previous approaches to quantum gravity such as Loop quantum gravity, is that it uses concepts from condensed matter physics such as quantum critical phenomena.
• July 4, 2012: the CMS and the ATLAS experimental teams at the LHC independently announced that they each confirmed the formal discovery of a previously unknown boson of mass between 125–127 GeV/c2, whose behavior so far has been “consistent with” a Higgs boson.

Sources

Abbott, David, ed. The Biographical Dictionary of Scientists: Physicists Peter Bedrick Books, 1984.

Bassett, Bruce and Ralph Edney. Introducing Relativity Totem Books, 2002.

Bernal, JD. A history of classical physics: From antiquity to the quantum Barnes and Noble Books, 1997.

Daintith, John. The Facts on File Dictionary of Physics (Facts on File Science Library) Facts on File, 1988.

Greene, Brian. The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory Vintage Books, 1999.

Gribbin, John. In Search of Schrodinger’s Cat Bantam Books, 1984.

Hawking, Stephen and Leonard Mlodinow. The Grand Design. Bantam Books, 2010.

Kumar, Manjit. Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality W. W. Norton and Company, 2008.

McEvoy, J. P. and Oscar Zarate. Introducing Stephen Hawking Totem Books, 1995.

Morris, Richard. The Universe, the Eleventh Dimension, and Everything: What We Know and How We Know It Four Walls Eight Windows, 1999.

Randall, Lisa. Warped Passages: Unraveling the Mysteries of the Universe’s Hidden Dimensions Harper Perennial, 2005.

Smolin, Lee. The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next Mariner Books, 2006.

Trigg, George L. Landmark Experiments in Twentieth Century Physics Dover Publications, 1995.

Have something to say? Leave a comment.