13.7 billion years ago The Big Bang
An unimaginably large explosion from an unimaginably small particle - according to modern theory the first moment of the universe

12 billion years ago First galaxies begin to form
The first galaxies begin to form, as self-contained gravitational systems with gases gradually coalescing into stars

4.6 billion years ago Milky Way and the sun
A new galaxy, the Milky Way, forms - and one of its stars is our sun

4.6 billion years ago Nuclear dust becomes solar system
The new star settles down, while nuclear dust in the vicinity coalesces into planets and asteroids orbiting the sun

500 BC Magnets found in Magnesia
The Greeks are intrigued by the iron-attracting property of a mineral which they find in the district of Magnesia

500 BC Electricity in amber
The Greeks observe the strange effect of electricity, seen when amber (known to them as electron) is rubbed

250 BC Archimedes leaps from bath
Archimedes (it is said) leaps out of his bath shouting eureka ('I have found it') when he perceives how to test for relative density

1600 Earth is a magnet says Elizabeth's physician
William Gilbert, physician to Queen Elizabeth, concludes that the earth is a magnet and coins the term 'magnetic pole'

1600 Electricity named
Electricity is given its name (in the Latin phrase vis electrica) by the English physician, William Gilbert

1638 Galileo launches mathematical physics
Galileo's Discorsi, published in Leiden, lays the groundwork for mathematical physics

1646 Pascal demonstrates atmospheric pressure
With the help of his more robust brother-in-law, Blaise Pascal provides physical proof that atmospheric pressure varies with altitude

1654 Sixteen horses foiled by vacuum
Otto von Guericke uses sixteen horses to demonstrate in Regensburg the power of a vacuum

1665 Newton in Lincolnshire garden
Isaac Newton spends a creative period in Lincolnshire, at home in Woolsthorpe Manor, apples or no apples

1672 Newton discovers nature of light
Isaac Newton's experiments with the prism demonstrate the link between wavelength and colour in light

1676 Speed of light only 25% out
Ole Roemer, a Danish astronomer working with Cassini in Paris, calculates the speed of light with an error of only 25%

1678 Huygens' wave theory of light
Christiaan Huygens expounds the theory that light consists of a vibration forming a ripple of waves

1687 Newton explains gravity
Newton publishes Principia Mathematica, proving gravity to be a constant in all physical systems

1714 Fahrenheit takes temperature
Fahrenheit perfects the mercury thermometer and decides on a 180-degree interval between the freezing and boiling points of water

1742 Celsius goes centigrade
Swedish astronomer Anders Celsius proposes 100 degrees between the freezing and boiling points of water

1745 The dean and the Leyden jar
The principle of the Leyden jar is discovered by an amateur German physicist, Ewald Georg von Kleist, dean of the cathedral in Kamin

1752 Franklin attracts lightning
Benjamin Franklin flies a kite into a thunder cloud to demonstrate the nature of electricity

1761 Black sees heat in ice
Scottish chemist and physicist Joseph Black observes the latent heat in melting ice

1785 Coulomb researches electricity
French physicist Charles Augustin de Coulomb begins publishing his discoveries in the field of electricity and magnetism

1800 First electric battery
Italian physicist Alessandro Volta describes to the Royal Society in London how his 'pile' of discs can produce electric current

1803 Dalton's Law
English chemist John Dalton reads a paper describing his Law of Partial Pressure in gases (discovered in 1801)

1817 Fraunhofer studies solar spectrum
German physicist Joseph von Fraunhofer observes and draws dark lines in the solar spectrum

1820 Ampère pioneers electrodynamics
French physicist André Marie Ampère begins his researches into the links between electricity and magnetism

1821 Fresnel analyzes light waves
French physicist Augustin Jean Fresnel publishes the theory that light is a transverse wave, thus explaining polarization effects

1827 Ohm publishes his law
German physicist Georg Simon Ohm formulates his law about the proportionality of current flowing in an electric conductor

1832 Laws of electrolysis
English scientist Michael Faraday reports his discovery of the first law of electrolysis, to be followed a year later by the second

1842 Doppler effect
Austrian physicist Christian Doppler explains the acoustic effect now known by his name

1848 Thomson proposes new scale of temperature
Scottish physicist William Thomson, later Lord Kelvin, proposes the 'absolute' scale of temperature

1851 Foucault's pendulum
French physicist Léon Foucault demonstrates the rotation of the earth by means of a long pendulum suspended in the Pantheon in Paris

1852 Second law of thermodynamics
Scottish physicist William Thomson formulates the second law of thermodynamics, concerning the transfer of heat within a closed system

1864 Maxwell's Equations
Scottish physicist James Clerk Maxwell presents to the Royal Society his discoveries in the field of electromagnetics, now known collectively as Maxwell's Equations

1878 Cathode rays observed in 'Crookes tubes'
William Crookes develops a special tube, now known as the Crookes tube, for the study of cathode rays

1894 Ramsay discovers argon
Scottish physicist William Ramsay isolates argon, following Rayleigh's discovery that an undiscovered gas combines with nitrogen in the air

1895 Roentgen discovers X-rays
German physicist Wilhelm Roentgen discovers rays that can penetrate light-proof barriers, and names them x-rays because their nature is as yet unknown

1896 Becquerel discovers radioactivity
French physicist Antoine Henri Becquerel discovers in uranium salt the phenomenon of natural radioactivity

1897 Thomson discovers electron
English physicist Joseph John Thomson, working at the Cavendish laboratory in Cambridge, discovers the existence of the electron

1900 Planck proposes quantum theory
German physicist Max Planck proposes the revolutionary concept of the quantum theory

1902 Kennelly-Heaviside layer
A.E. Kennelly and Oliver Heaviside independently see the link between the atmosphere and the behaviour of radio waves

1903 Radioactive half-life discovered
Ernest Rutherford and Frederick Soddy identify the phenomenon of radioactive half-life

1905 Electromagnetic radiation of light
Albert Einstein explains the photoelectric effect as a flow of discreet particles (quanta) of electromagnetic radiation

1905 Einstein's special theory of relativity
In his special theory of relativity Albert Einstein reconciles the apparent clash between relativity and electromagnetic theory

1905 e = mc²
Albert Einstein relates mass and energy in the equation e = mc²

1906 Third Law of Thermodynamics is fornulated
German physicist Walther Nernst establishes the Third Law of Thermodynamics, dealing with temperatures close to absolute zero

1908 Geiger Counter
German physicist Hans Geiger, working in England with Rutherford, develops an instrument that can detect and count alpha particles

1909 Millikan’s oil drop experiment
US physicist Robert A. Millikan devises an oil drop experiment that determines the charge of an electron

1911 Wilson tracks particles in cloud chamber
Charles Wilson, using his cloud chamber to detect the passage of charged particles, obtains his first photographs of alpha and beta rays

1911 Rutherford and the nucleus
Ernest Rutherford proposes the concept of the nucleus as a positively charged mass at the centre of an atom

1913 Einstein discovers photochemical equivalence
Albert Einstein formulates the law of photochemical equivalence, a fundamental principle of chemical reactions induced by light

1913 Braggs pioneer X-ray crystallography
Lawrence Bragg and his father, William, together develop X-ray crystallography, based on the diffraction patterns of crystals

1913 Bohr finds new application for quantum theory
The Danish physicist Niels Bohr uses quantum theory as a key to understanding the structure of the atom

1913 Moseley refines periodic table
English physicist Henry Moseley proposes that the atomic number of an element is a physical reality, thus laying the basis for the modern periodic table

1915 Einstein's general theory of relativity
Einstein submits a paper, The field equations of gravitation, containing the sums required to explain the general theory of relativity

1925 Heisenberg and quantum mechanics
23-year-old German physicist Werner Heisenberg publishes his ground-breaking theory of quantum mechanics

1925 Pauli's exclusion principle
Austrian physicist Wolfgang Pauli formulates his exclusion principle, stating that no two electrons in an atom can have the same four quantum numbers

1927 Heisenberg's Uncertainty Principle
Werner Heisenberg publishes his Uncertainty Principle, declaring that it is impossible to define precisely the position and momentum of a sub-atomic particle

1930 Pauli predicts the neutrino
Wolfgang Pauli announces his mathematical proof of the existence of the particle subsequently known as the neutrino

1930 Dirac predicts the positron
British theoretical physicist Paul Dirac predicts the existence of an anti-particle of the electron, first observed two years later and named the positron

1932 Atom split in Cambridge
John Cockcroft and Ernest Walton are the first to split an atom, by bombarding it with accelerated protons

1932 Chadwick and the neutron
British physicist James Chadwick shows that the behaviour of subatomic particles can be explained by the existence of neutrons, or particles with no electrical charge

1934 Joliot and Curie discover artificial radioactivity
Frédéric and Irène Joliot-Curie discover artificial radioactivity

1939 Nuclear fission
German physicists, led by Otto Hahn, announce their discovery of nuclear fission

1939 August 2 Einstein alerts Roosevelt to nuclear dangers
German-born US physicist Albert Einstein writes to President Roosevelt, warning of the potential of an atomic bomb

1940 Britain protected by radar
Radar masts along the coasts of Britain give early warning of German air attacks

1942 June 7 Oppenheimer directs Manhattan Project
US physicist J. Robert Oppenheimer is appointed director of the Manhattan Project to develop a nuclear weapon

1942 December 2 Nuclear chain reaction
Enrico Fermi and his team in Chicago achieve the first nuclear chain reaction

1945 July 16 USA has atom bomb
US scientists succeed in exploding an atom bomb at Alamogordo, a test site in the New Mexican desert

1945 August 6 Atom bomb over Hiroshima
An atom bomb is dropped on Hiroshima, destroying four square miles of the city and killing 80,000 people

1946 Bikini Atoll
The first of about 20 US tests of atomic and hydrogen bombs is carried out on Bikini Atoll, in the Pacific

1947 Gabor invents the hologram
Hungarian-born British engineer Dennis Gabor creates the first three-dimensional image from reflected light, subsequently known as a hologram

1947 The first transistor
The first transistor is produced in the Bell Laboratories in Murray Hill, New Jersey

1949 USSR tests atomic bomb
The first Soviet atomic bomb, called by the Americans Joe One, is successfully tested in Kazakhstan

1950 Truman gives priority to hydrogen bomb
In response to the Soviet atom bomb, President Truman announces a crash programme to develop a hydrogen bomb

1951 Field ion microscope observes atoms
Erwin Müller completes his development of the field ion microscope, the first instrument capable of observing atoms

1951 US achieves nuclear fusion
The first hydrogen bomb is successfully tested by the US at Enewetak Atoll in the Marshall Islands

1952 Franklin photographs DNA
X-ray crystallographer Rosalind Franklin, working at King's College in London, photographs DNA

1953 USSR tests hydrogen bomb
The first Soviet hydrogen bomb is successfully tested at the Semipalatinsk Test Site in Kazakhstan

1964 Cosmic background radiation
US physicists Arno Penzias and Robert Wilson discover cosmic background radiation, lending strong support to the Big Bang theory

1974 Hawking radiation
British physicist Stephen Hawking describes how black holes can emit radiation, a process now known as 'Hawking radiation'

1988 Brief History of Time
British physicist Stephen Hawking explains the cosmos for the general reader in A Brief History of Time: from the Big Bang to Black Holes

2015 September 14 Gravitational waves detected
Gravitational waves are detected for the first time, by LIGO