Coming of Age in the Milky Way - Timothy Ferris (2003)


Time: 0

Noteworthy Events*: Origin of time, space, and energy—of the universe as we know it.

Time: 10−41 second ABT

Noteworthy Events: End of Planck epoch; gravitational radiation comes out of thermal equilibrium with the rest of universe.

Time: 10−34 second

Noteworthy Events: Universe, in vacuum state, begins “inflating”—i.e., expanding at an exponential rate, some 1050 times present expansion rate.

Time: 10−30 second

Noteworthy Events: Inflationary epoch ends; particles precipitate out of the vacuum.

Time: 10−11 second

Noteworthy Events: Symmetry-breaking phase transition shatters the electroweak force into the electromagnetic and weak nuclear forces.

Time: 10−6-10−5 second

Noteworthy Events: Quarks and antiquarks cease mutual annihilation. The survivors link up in trios as protons and neutrons, the components of all future atomic nuclei.

Time: 10−4 second

Noteworthy Events: Universe 1/10,000 second old. Constant capture of electrons and positrons turns neutrons into protons and vice versa. As slightly more energy is required to make neutrons than protons, the process leaves the universe with five times as many protons as neutrons.

Time: 102 second

Noteworthy Events: Particles of matter and energy interact in thermal equilibrium.

Time: 1 second

Noteworthy Events: Neutrinos, previously embroiled with other particles, decouple and go their own way.

Time: 3 minutes 42 seconds

Noteworthy Events: Protons and neutrons have linked up, forming nuclei of helium. Universe now composed of about 20 percent helium nuclei, 80 percent hydrogen.

Time: 1 hour

Noteworthy Events: Universe has cooled to the point that most nuclear processes have stopped.

Time: 1 year

Noteworthy Events: Ambient temperature of universe about that of the center of a star.

Time: < 106 years

Noteworthy Events: Origin of cosmic background radiation. Photons decouple, leaving electrons free to combine with nuclei, forming stable atoms. Hereafter, matter can begin to congeal into galaxies and stars.

Time: - 109 years ABT
(≈ 13 billion years BP*)

Noteworthy Events: Protogalaxies, globular clusters forming. Epoch of quasars begins.

Time: 4.5 billion years BP

Noteworthy Events: Sun and planets congeal from a cloud of gas and dust in a spiral arm of the Milky Way galaxy.

Time: 3.8 billion years BP

Noteworthy Events: Earth has cooled sufficiently for solid crust to form; age of oldest dated terrestrial rocks.

Time: 3.5–3.2 billion years

Noteworthy Events: Microscopic living cells evolve on Earth.

Time: 1.8–1.3 billion years

Noteworthy Events: Plants appear. Oxygen poisons Earth’s atmosphere, and aerobic (“oxygen-loving”) organisms proliferate.

Time: 900–700 million years

Noteworthy Events: Advent of sex accelerates the pace of biological evolution.

Time: 700 million years

Noteworthy Events: Animals—mostly flatworms and jellyfish—appear.

Time: 600 million years

Noteworthy Events: First crustaceans.

Time: 500 million years

Noteworthy Events: First vertebrates.

Time: 425 million years

Noteworthy Events: Life migrates to dry land.

Time: 395 million years

Noteworthy Events: First insects.

Time: 325 million years

Noteworthy Events: First land vertebrates.

Time: 200 million years

Noteworthy Events: First mammals.

Time: 180 million years

Noteworthy Events: North America separates from Africa; genesis of the Atlantic.

Time: 100 million years

Noteworthy Events: Half a galactic year ago; Earth looks out on the other side of the universe.

Time: 70 million years

Noteworthy Events: Preprimates evolve.

Time: 55 million years

Noteworthy Events: Early horses appear.

Time: 35 million years

Noteworthy Events: Early cats, dogs.

Time: 24 million years

Noteworthy Events: Appearance of grass.

Time: 21 million years

Noteworthy Events: Apes, monkeys depart along separate evolutionary pathways.

Time: 20 million years

Noteworthy Events: Atmosphere approaches modern composition.

Time: 15 million years

Noteworthy Events: Antarctica freezes over.

Time: 11 million years

Noteworthy Events: Grazing animals proliferate.

Time: 5 million years

Noteworthy Events: Apeman diverges from chimpanzee family.

Time: 3.7 million years

Noteworthy Events: Apemen walk upright.

Time: 3.5 million years

Noteworthy Events: Onset of latest series of ice ages.

Time: 1.8–1.7 million years

Noteworthy EventsHomo erectas, “first true man,” in China.

Time: 600,000 years

Noteworthy EventsHomo sapiens emerges.

Time: 360,000 years

Noteworthy Events: Controlled use of fire common among genus Homo.

Time: 150,000 years

Noteworthy Events: Woolly mammoth roam.

Time: 100,000 years

Noteworthy Events: Stars take on the forms of the recognizable modern constellations.

Time: 40,000 years

Noteworthy Events: Invention of complex language; modern humans flourish.

Time: 35,000 years

Noteworthy Events: Neanderthal man disappears. First musical instruments are crafted.

Time: 20,000–15,000 years

Noteworthy Events: Agriculture invented.

Time: 19,000 years

Noteworthy Events: Peopling of the Americas begins.

Time: 18,000 years

Noteworthy Events: Animals are herded by humans.

Time: 14,000 years

Noteworthy Events: Invention of fishhooks.

Time: 13,000 years

Noteworthy Events: Development of ceramic pottery.

Time: 10,000 years

Noteworthy Events: Cultivation of wheat, rice begins.

Time: 6,700 years

Noteworthy Events: Early Babylonian calendar in use.

Time: 6,200 years

Noteworthy Events: Refined solar calendar employed.

Time: 6,500 years

Noteworthy Events: Copper is smelted.

Time: 5,600 years

Noteworthy Events: First taxes.

Time: 5,500 years
BP (= 3,500 BC)

Noteworthy Events: Development of writing.

Time: 3,600–3,400 BC

Noteworthy Events: Cotton cultivated in Peru, Mexico.

Time: 2,500 years

Noteworthy Events: Stonehenge built.

Time: 2,200 years

Noteworthy Events: Systematic astronomy in Egypt, Babylonia, India, China.

Time: 1,500 years

Noteworthy Events: Sundial invented, in Egypt.

Time: 1,000 years

Noteworthy Events: Homer declaims the Odyssey.

Time: 800 years

Noteworthy Events: Olmec culture in Mexico.

Time: 700 years

Noteworthy Events: Hesiod, Works and Days.

Time: 650 years

Noteworthy Events: Mayan culture in Guatemala.

Time: 600 years

Noteworthy Events: Lao-tzu, Confucius, Buddha, Zoroaster; Old Testament in Hebrew.

Time: 540 years

Noteworthy Events: Pythagoras teaches that “all is number” and that nature is harmonious.

Time: 450 years

Noteworthy Events: Leucippus and Democritus propose that matter is made of indivisible entities, the atoms. Paradoxes of Zeno raise doubts about the concept of the infinitesimal.

Time: 400 years

Noteworthy Events: Plato teaches that the material world is but a shadow of a geometrically perfect reality. Aristotle, Eudoxus, theorize that universe is composed of crystalline spheres centered on Earth.

Time: 300 years

Noteworthy Events: Euclid’s geometry marries mathematical perfection to the world of experience.

Time: 260 years

Noteworthy Events: Aristarchus of Samos hypothesizes that the earth orbits the sun in a gigantic universe.

Time: 100 years

Noteworthy Events: Chinese seafarers reach the east coast of India.

Time: 60 BC

Noteworthy Events: Lucretius writes De Rerum Natura (On the Nature of Things), espousing Epicurean cosmology.

Time: AD 100

Noteworthy Events: Claudius Ptolemy constructs a complex geocentric cosmological model that “saves the appearances”—i.e., makes reasonably accurate predictions at the expense of claims to represent physical reality.

Time: 325

Noteworthy Events: Eusebius, chairman of the Council of Nicaea convened by the emperor Constantine, estimates that the world was created 3,184 years prior to the birth of Abraham.

Time: 400

Noteworthy Events: Middle or Dark Ages begin; science dormant in the West.

Time: 455

Noteworthy Events: Vandals sack Rome.

Time: 963

Noteworthy Events: Al Sufi, in his Book of the Fixed Stars, mentions nebulae.

Time: 1001

Noteworthy Events: Leif Ericsson reaches New England.

Time: 1276–1292

Noteworthy Events: Marco Polo in Hangchow.

Time: 1400

Noteworthy Events: Renaissance of learning commences in Europe.

Time: 1492

Noteworthy Events: Columbus (re)discovers America.

Time: 1521

Noteworthy Events: Cortez takes Mexico.

Time: 1522

Noteworthy Events: Survivors of Magellan’s final expedition complete circumnavigation of the globe.

Time: 1523

Noteworthy Events: Pizarro takes Peru.

Time: 1543

Noteworthy Events: Copernicus’s On the Revolutions published.

Time: 1572

Noteworthy Events: Tycho sees a nova (or “new star”) in the sky, evidence against Aristotle’s theory that the realm of the stars is unchanging and therefore unlike that of the earth.

Time: 1576

Noteworthy Events: Thomas Digges in England publishes a defense of the Copernican cosmology in which he portrays the stars as distributed throughout infinite space.

Time: 1604

Noteworthy Events: Galileo proposes that bodies fall with a uniformly accelerated motion, thus enunciating the first of the laws of classical dynamics.

Noteworthy Events: Kepler and Galileo observe a supernova.

Time: 1609

Noteworthy Events: Galileo first observes the night sky through a telescope.

Noteworthy Events: Kepler demonstrates that the orbits of the planets are elliptical.

Time: 1611

Noteworthy Events: Edition of the King James Bible published containing an estimate by James Ussher, bishop of Armagh, that “the beginning of time … fell on the beginning of the night which preceded the 23 rd day of October, in the year … 4004 B.C.”

Time: 1616

Noteworthy Events: Roman Catholic Church bans all books that maintain that the earth moves.

Time: 1639

Noteworthy Events: Transit of Venus observed by two English amateur astronomers.

Time: 1662

Noteworthy Events: Royal Society chartered in London.

Time: 1665–1666

Noteworthy Events: Isaac Newton, age twenty-three, home from college, realizes that gravitational force obeying an inverse-square law would account alike for falling bodies on earth and the motion of the moon in its orbit.

Time: 1666

Noteworthy Events: Newton observes spectrum produced by sunlight when shown through a prism.

Time: 1672

Noteworthy Events: Opposition of Mars widely observed, by Richer at Cayenne and Cassini in Paris among others, leading to estimates of the distance from the earth to the sun of some eighty-one to eighty-seven million miles—90 percent of the correct value.

Time: 1675

Noteworthy Events: Olaus Römer determines, from studying the satellites of Jupiter, that light has a finite velocity.

Time: 1684

Noteworthy Events: Edmond Halley visits Isaac Newton at Trinity College, resurrects line of research that leads Newton to write the Principia.

Time: 1686

Noteworthy Events: Bernard de Fontenelle’s Entretiens sur la Plurality des Mondes popularizes the idea that the universe contains many inhabited worlds.

Time: 1687

Noteworthy Events: Newton’s Principia published.

Time: 1716

Noteworthy Events: Halley urges that future transit of Venus may be observed and timed in order to triangulate interplanetary distances.

Time: 1718

Noteworthy Events: Halley finds that the bright stars Sirius, Aldebaran, Betelgeuse, and Arcturus have changed their position in the sky since Ptolemy’s Almagest was compiled—first evidence of the “proper motion” of stars.

Time: 1719

Noteworthy Events: John Strachey in England publishes notes on strata in the coal-rich district of Somerset, an early step in the establishment of geological science.

Time: 1728

Noteworthy Events: James Bradley finds aberration in starlight produced by the motion of the earth.

Time: 1750–1784

Noteworthy Events: French amateur astronomer Charles Messier catalogs scores of indistinct celestial objects that might be mistaken for comets; many will prove to be star clusters and interstellar gas clouds, others external galaxies.

Time: 1755

Noteworthy Events: Kant proposes that spiral nebulae are galaxies of stars.

Time: 1761, 1769

Noteworthy Events: Transits of Venus observed by widely scattered scientific expeditions, permitting new determinations of the distance from the earth to the sun—the “astronomical unit.”

Time: 1765

Noteworthy Events: John Harrison is acknowledged by the English Board of Longitude to have developed the marine chronometer, making possible accurate timekeeping and the determination of longitude at sea.

Time: 1766

Noteworthy Events: Henry Cavendish identifies hydrogen, the most abundant element in the universe.

Time: 1781

Noteworthy Events: William Herschel discovers the planet Uranus.

Time: 1783

Noteworthy Events: Herschel derives the general direction of the solar system’s motion through space, by studying the proper motion of thirteen bright stars.

Time: 1793

Noteworthy Events: William Smith, a canal surveyor and consulting engineer excavating the Somersetshire Coal Canal, finds evidence for a consistent sequence of geological strata throughout England.

Time: 1795

Noteworthy Events: James Hutton’s Theory of the Earth advances a uniformitarian hypothesis of geological change having taken place in the course of a lengthy past.

Time: 1800

Noteworthy Events: William Herschel detects infrared light.

Time: 1801

Noteworthy Events: Johann Ritter detects ultraviolet light.

Noteworthy Events: Georges Cuvier identifies twenty-three species of extinct animals in the fossil record, confounding the doctrine that all species were created simultaneously and are imperishable.

Time: 1802

Noteworthy Events: William Wollaston discovers spectral lines in the spectrum of the sun.

Time: 1814

Noteworthy Events: Joseph Fraunhofer, using the first grating spectroscope, rediscovers solar spectral lines and charts them, laying the basis for astrophysical spectroscopy.

Time: 1820

Noteworthy Events: Hans Christian Örsted discovers that electric current produces a magnetic field, ushering in the study of electromagnetic force.

Time: 1823

Noteworthy Events: John Herschel proposes that Fraunhofer lines may indicate the presence of metals in the sun.

Time: 1830

Noteworthy Events: Charles Lyell publishes the first volume of his Principles of Geology, presenting evidence for the uniformitarian theory that the geological record can be explained in terms of the slow action, over aeons of time, of processes that continue in the world today.

Time: 1831

Noteworthy Events: Charles Darwin, a copy of Lyell’s book in hand, departs aboard the Beagle on a five-year voyage around the world.

Time: 1832

Noteworthy Events: Darwin adduces the essential elements of his theory of evolution by natural selection, but does not publish the theory for another twenty-two years.

Time: 1833

Noteworthy Events: First precise measurement, by means of parallax, of the distance to a star.

Time: 1842

Noteworthy Events: Christian Johann Doppler points out that the wavelength of sound or other emissions from a moving source will appear to a stationary observer to be higher in frequency if the object is approaching, lower if it is receding—the “Doppler shift.”

Time: 1847

Noteworthy Events: Hermann von Helmholtz proposes the law of conservation of energy.

Time: 1849

Noteworthy Events: Jean-Léon Foucault detects spectral emission lines.

Time: 1850

Noteworthy Events: First astronomical photograph—a daguerreotype of the moon—is made, by W. C. Bond at Harvard.

Time: 1855–1863

Noteworthy Events: Robert Bunsen and Gustav Kirchhoff workout the basics of spectral analysis, by which the spectra of laboratory materials can be compared with those of the sun and stars.

Time: 1859

Noteworthy Events: Darwin’s Origin of Species published.

Time: 1862

Noteworthy Events: Foucault refines estimates of the velocity of light.

Time: 1864

Noteworthy Events: William Huggins obtains the first spectrum of a nebula, finds that it is composed of gas.

Noteworthy Events: James Clerk Maxwell publishes a unified theory of electricity and magnetism, portraying both as aspects of electromagnetic force.

Time: 1865

Noteworthy Events: Gregor Mendel announces results of his research in genetics, revealing key to persistence of unchanging traits in living things, a critical missing element in Darwinism.

Time: 1874, 1882

Noteworthy Events: Transits of Venus observed with new, more precise instruments, improving estimates of the astronomical unit.

Time: 1877

Noteworthy Events: David Gill measures parallax of Mars during its opposition, deduces distance to the sun of ninety-three million miles.

Time: 1879

Noteworthy Events: Albert Michelson, employing Foucault’s principle, determines velocity of light.

Time: 1883

Noteworthy Events: Henry Rowland’s diffraction grating greatly improves the resolution of spectrographs.

Time: 1884

Noteworthy Events: Johann Balmer determines harmonic sequence of hydrogen lines, initiating line of inquiry that will lead to investigation of the electron shells of atoms.

Time: 1887

Noteworthy Events: Albert Michelson and Edward Morley perform the final and most precise in a series of experiments showing that space cannot be filled with the aether that had been thought to be responsible for transmitting light. Their work clears the ground for the ascent of the Lorentz contractions.

Time: 1892

Noteworthy Events: Hendrik Lorentz and George FitzGerald independently propose that contraction of length of measuring rods with velocity explains the Michelson-Morley experimental results, a concept essential to the special theory of relativity.

Time: 1895

Noteworthy Events: E. E. Barnard photographs the Milky Way, notes that dark patches are too numerous to be empty space but must represent dark clouds of interstellar matter.

Time: 1897

Noteworthy Events: J. J. Thomson discovers the electron.

Time: 1898

Noteworthy Events: Marie and Pierre Curie isolate the radioactive elements radium and polonium.

Time: 1900

Noteworthy Events: Max Planck proposes the quantum theory of radiation, the basis of quantum physics.

Time: 1904

Noteworthy Events: Ernest Rutherford suggests that the amount of helium produced by the radioactive decay of minerals in rocks could be employed to measure the age of the earth.

Time: 1905

Noteworthy Events: Albert Einstein publishes special theory of relativity, indicating that measurements of space and time are distorted at high velocity and implying that mass and energy are equivalent; in another paper he shows that light is composed of quanta.

Noteworthy Events: Jacobus Kapteyn, studying the proper motions of twenty-four hundred stars, finds evidence of what he calls “star streaming”—that stars in our neighborhood move in a preferred direction—an early clue to the rotation of our galaxy.

Time: 1911

Noteworthy Events: Ernest Rutherford determines that most of the mass of atoms is contained in their tiny nuclei.

Time: 1912

Noteworthy Events: Henrietta Swan Leavitt discovers a correlation between the absolute magnitude and the period of variability of Cepheid variable stars, opening the door to their use as intergalactic distance indicators.

Time: 1913

Noteworthy Events: Niels Bohr develops theory of atomic structure, in which electrons are said to orbit the nucleus in a manner somewhat akin to that of planets orbiting the sun.

Noteworthy Events: Henry Norris Russell presents a plot of the luminosities and colors of stars, extending work done in 1911 by Ejnar Hertzsprung. The resulting Hertzsprung-Russell diagram will be fundamental to the understanding of the evolution of stars.

Time: 1914

Noteworthy Events: Walter Adams and Arnold Kohlschutter determine the absolute luminosity of stars from their spectra alone, making it possible to estimate the distances of millions of distant stars.

Time: 1915

Noteworthy Events: Annie Jump Cannon classifies stars into categories according to their spectral type, a major step in discerning order underlying the diversity of the stars.

Time: Arnold Sommerfeld refines Bohr model of the atom.

Time: 1916

Noteworthy Events: Albert Einstein publishes the general theory of relativity, portraying gravitation as an effect of curved space and delivering cosmology from the ancient dilemma of a finite versus an infinite universe.

Time: 1916–1917

Noteworthy Events: Arthur Stanley Eddington demonstrates theoretically that stars are gaseous spheres; his work lays the foundation for his later assertion that gravitational contraction cannot be the mechanism that powers the stars.

Time: 1917

Noteworthy Events: Heber Curtis and George Ritchey announce that they have found novae (stars that have suddenly increased tremendously in brightness) in the Andromeda spiral. Opinions differ on whether this means Andromeda is a galaxy of stars, or a gaseous nebula from which new stars are condensing.

Noteworthy Events: Vesto Slipher measures large Doppler shifts in the spectra of spirals, later found to be due to the motion of the spiral galaxies in the expanding universe.

Time: 1918

Noteworthy Events: Harlow Shapley determines, by studying the distances of globular clusters, that the sun lies toward one edge of a galaxy of stars.

Noteworthy Events: The 100-inch telescope at Mount Wilson, then the world’s largest, begins operation.

Time: 1919

Noteworthy Events: English expedition to observe a solar eclipse confirms Einstein’s prediction that space, in a gravitational field, is strongly curved.

Time: 1920

Noteworthy Events: The controversy over whether spiral nebulae are gaseous clouds or “island universes”—i.e., galaxies—comes to a head in a debate between Heber Curtis and Harlow Shapley.

Time: 1922

Noteworthy Events: Ernst Öpik deduces, from rotation velocities and the mass to luminosity ratio of the Andromeda spiral, that it is a galaxy in its own right.

Noteworthy Events: Aleksandr Friedmann shows that general relativity is consistent with an expanding-universe cosmology.

Time: 1923

Noteworthy Events: Cecilia Payne demonstrates, from solar spectra, that the relative abundance of elements in the sun approximates that in the crust of the earth.

Time: 1924

Noteworthy Events: Louis de Broglie develops wave theory of matter.

Time: 1925

Noteworthy Events: Max Born, Pascual Jordan, and Werner Heisenberg develop quantum mechanics.

Noteworthy Events: Wolfgang Pauli announces the exclusion principle, essential to understanding spectral lines of stars and nebulae.

Noteworthy Events: Bertil Lindblad demonstrates that the motion of stars called “star streaming” by Kapteyn in 1905 can be explained as being due to the rotation of the Milky Way galaxy.

Noteworthy Events: Edwin Hubble announces that he has identified Cepheid variable stars in the Andromeda galaxy, confirming that it is a galaxy of stars rather than a gaseous nebula and making it possible to measure its distance.

Time: 1926

Noteworthy Events: Erwin Schrödinger proposes wave-mechanical theory of the atom.

Noteworthy Events: Lindblad produces theory of rotation of the Milky Way galaxy.

Time: 1927

Noteworthy Events: Jan Oort detects evidence of the rotation of the Milky Way galaxy, by examining the radial velocities of stars.

Noteworthy Events: Georges Lemaître publishes an expanding-universe cosmology.

Noteworthy Events: Werner Heisenberg discovers the quantum indeterminacy principle.

Time: 1927–1929

Noteworthy Events: Relativistic quantum electrodynamics theory developed.

Time: 1928

Noteworthy Events: George Gamow applies the uncertainty principle to the problem of how protons combine to build nuclei in stellar interiors, a signal step in establishing that nuclear fusion provides the energy that powers stars.

Noteworthy Events: Ira Bowen determines that the spectra of nebulae are produced by doubly ionized oxygen and not by an unknown element called “nebulium,” as had been thought. This strengthens the hopes of astrophysicists that the rest of the universe is made of the same elements and obeys the same natural laws as here on Earth.

Noteworthy Events: Dirac publishes the “Dirac equation,” a relativistic quantum theory of electromagnetism.

Time: 1929

Noteworthy Events: Edwin Hubble announces a relationship between the redshift in the spectra of galaxies and their distances, indicating that the universe is expanding.

Time: 1930

Noteworthy Events: Robert Trumpler’s studies of open star clusters enable him to measure the extent to which interstellar clouds dim and redden starlight, greatly improving estimates of the distances of stars.

Time: 1931

Noteworthy Events: Dirac predicts the existence of the positron, the antimatter equivalent of the electron.

Noteworthy Events: Wolfgang Pauli, studying beta decay, predicts the existence of the neutrino.

Noteworthy Events: Kurt Gödel’s second incompleteness theorem indicates that the consistency of any system, including scientific systems, cannot be proved internally—i.e., that mathematics, and science are inherently open-ended.

Time: 1932

Noteworthy Events: James Chadwick discovers the neutron.

Noteworthy Events: Carl Anderson, without knowing of Dirac’s 1931 paper postulating its existence, discovers the positron.

Noteworthy Events: Karl Jansky finds that the Milky Way emits radio waves, opening door on the science of radio astronomy.

Time: 1935

Noteworthy Events: Hideki Yukawa predicts existence of the meson.

Time: 1939

Noteworthy Events: Niels Bohr and John Archibald Wheeler develop the theory of nuclear fission.

Noteworthy Events: Hans Bethe and Carl Friedrich von Weizsäcker independently arrive at theory of the carbon and proton-proton reactions in stars.

Time: 1940

Noteworthy Events: Grote Reber constructs a backyard radio telescope, makes the first radio map of the Milky Way.

Time: 1943

Noteworthy Events: Carl Seyfert identifies Seyfert galaxies, the first of a larger class of galaxies found to have bright nuclei that emit abnormal amounts of energy.

Time: 1944

Noteworthy Events: Walter Baade resolves the central region of the Andromeda galaxy into stars, establishing a fundamental distinction between the older, redder stars characteristic of the centers of spiral galaxies, and the younger, bluer stars found in their spiral arms.

Time: 1945

Noteworthy Events: Hendrik van de Hülst predicts that clouds of interstellar hydrogen emit radio energy at the 21-centimeter wavelength.

Time: 1946

Noteworthy Events: James Hey, S. J. Parsons, and J. W. Phillips identify a powerful radio source in Cygnus, initiating research that leads to finding galaxies that emit enormous amounts of energy at radio wavelengths.

Time: 1948

Noteworthy Events: Dedication of the 200-inch telescope on Palomar Mountain.

Noteworthy Events: Ralph Alpher and George Gamow theorize about the physics of the early universe; Alpher and Robert Herman, correcting Gamow’s arithmetic, then predict that the big bang should have produced a cosmic microwave background radiation.

Time: 1948–1949

Noteworthy Events: “Renormalization” of quantum electrodynamics removes unwanted infinities from the equations.

Time: 1948–1950

Noteworthy Events: Willard Frank Libby develops technique of radiocarbon dating.

Time: 1949

Noteworthy Events: John Bolton, Gordon Stanley, and O. B. Slee use radio interferometry to identify three radio sources with visible objects; two of them are galaxies, suggesting that what had been thought to be radio “stars” are actually objects lying much farther away in space.

Time: 1951

Noteworthy Events: Harold Ewen and Edward Purcell, closely followed by C. Alex Muller and Jan Oort, detect 21-centimeter radio radiation emitted by interstellar clouds.

Time: 1952

Noteworthy Events: Baade clears up serious discrepancies in the cosmic distance scale when he finds that the Cepheid variable stars used in measuring intergalactic distances actually come in two varieties, with different magnitude-periodicity relationships,

Time: 1953

Noteworthy Events: Murray Gell-Mann proposes a new quantum number called strangeness, notes that it is conserved in strong interactions.

Time: 1954

Noteworthy Events: Walter Baade and Rudolph Minkowski identify the radio source Cygnus A with a distant galaxy.

Noteworthy Events: Chen Ning Yang and Robert Mills develop a gauge symmetrical field theory, a major step toward viewing the universe in terms of underlying symmetries that were broken in early cosmic evolution.

Time: 1956

Noteworthy Events: Yang and Tsung Dao Lee theorize that parity is not conserved in weak interactions—i.e., that the weak force does not function symmetrically. Experiments conducted by Chien-Shiung Wu and collaborators the same year confirm their prediction.

Time: 1957

Noteworthy Events: Julian Schwinger proposes that the electromagnetic and weak forces are but aspects of a single variety of interaction.

Time: 1958

Noteworthy Events: Oort and colleagues use radio telescopes to map the spiral arms of the Milky Way galaxy.

Time: 1960

Noteworthy Events: Allan Sandage and Thomas Matthews discover quasars.

Time: 1961

Noteworthy Events: Gell-Mann and Yuval Ne’eman independently arrive at the “eightfold way” scheme of classifying subatomic particles that react to the strong nuclear force.

Time: 1963

Noteworthy Events: Maarten Schmidt finds redshift in the spectral lines of a quasar, indicating that quasars are the most distant class of objects in the universe.

Time: 1964

Noteworthy Events: Murray Gell-Mann and George Zweig independently propose that protons, neutrons, and other hadrons are composed of still smaller particles, which Gell-Mann dubs “quarks.”

Noteworthy Events: The omega-minus particle is detected at Brookhaven National Laboratory, confirming a prediction of the Gell-Mann-Ne’eman “eightfold way.”

Time: 1965

Noteworthy Events: Arno Penzias and Robert Wilson discover the cosmic microwave background radiation, light left over from the big bang.

Time: 1967

Noteworthy Events: Chia Lin and Frank Shu show that the spiral arms of galaxies may be created by density waves propagating across the galactic disk.

Noteworthy Events: Jocelyn Bell and Antony Hewish discover pulsars, leading to verification of the existence of extremely dense “neutron stars.”

Time: 1968

Noteworthy Events: Experiments at the Stanford Linear Accelerator Center support the theory that hadrons are made of quarks.

Time: 1981

Noteworthy Events: Alan Guth postulates that the early universe went through an “inflationary” period of exponential expansion.

Time: 1983

Noteworthy Events: Electroweak unified theory verified in collider experiments at CERN. Attempts accelerate to arrive at a unified theory of all four forces.

Time: 1987

Noteworthy Events: Proton-decay experiments in the United States and Japan detect neutrinos broadcast by a supernova in the Large Magellanic Cloud, ushering in the new science of observational neutrino astronomy.

Time: 1988

Noteworthy Events: Quasars are detected near the outposts of the observable universe; their redshifts indicate that their light has been traveling through space for some seventeen billion years.

Time: 1990

Noteworthy Events: COBE satellite measures cosmic microwave background radiation; confirms that it displays a black-body spectrum as predicted by the hot big-bang model.

Time: 1992

Noteworthy Events: COBE satellite data show anisotropies—lumps—in the cosmic microwave background, supporting big-bang prediction that such lumps were the seeds of galaxies and other large-scale cosmic structures.

Time: 1998

Noteworthy Events: Astronomers studying Supernovae find evidence that the expansion of the universe is accelerating, rather than slowing down as had been presumed.

Time: 2000

Noteworthy Events: Measurements of cosmic microwave background anisotropies indicate that cosmic spacetime is flat or nearly so, as predicted by inflationary versions of big-bang theory.

Time: 2003

Noteworthy Events: WMAP satellite makes high-precision map of cosmic microwave background, supporting earlier CMB studies and yielding an age for the universe of 13.7 billion years, to a quoted accuracy of one percent.

*Most dates—and, for that matter, events—are approximate.

ABT = After the beginning of time.

*BP = Before Present