425 bc

Democritus proposes that all mater is made of small indivisible particles that he calls “atoms.”

280 bc

Aristarchus of Samos determines the relative distances of the sun and the moon from the earth. He also determines the relative sizes of the sun, the moon and the earth. These considerations lead him to propose that the earth revolves around the sun.

240 bc

Archimedes discovers his principle of buoyancy (Archimedes’ Principle).

235 bc

Eratosthenes develops a method to measure the circumference of the earth.

130 bc

Hipparchus estimates the size of moon from the parallax of an eclipse.

130

Ptolemy develops his a theory of the motion of the heavenly bodies. According to his theory, the earth is at the center of the universe and the sun and known planets revolve around it.

1269

Petrus de Maricourt conducts experiments with magnets and magnetic compasses.

1514

Nicolaus Copernicus develops his heliocentric theory. He publishes it in 1543, a few days before his death.

1592

Galileo Galilei invents the thermometer.

1600

William Gilbert publishes De Magnete which starts the modern treatment of magnetism. He also shows that the earth is a magnet.

1604

Galileo Galilei proves that falling bodies are accelerated towards the ground at a constant rate. He also shows that the distance for a falling object increases as the square of the time.

1609

Johannes Kepler publishes his First and Second laws of planetary motion in a book entitled Astronomia Nova.

1609

Galileo Galilei builds a telescope after hearing of its invention.

1613

Galileo Galilei introduces his principle of inertia.

1619

Johannes Kepler publishes his Third law of planetary motion.

1621

Willebrord van Roijen Snell introduces the law of refraction.

1638

Galileo introduces the concept of the relativity of motion in his Two New Sciences.

1651

Blaise Pascal shows that pressure applied at one point in a liquid is transmitted unchanged to all points in the liquid (Pascal’s Principle).

1662

Robert Boyle, while experimenting with gases, shows that if a fixed amount of a gas is kept at a constant temperature, the pressure and the volume of the gas follow a simple mathematical relationship.

1665-1966

Isaac Newton begins his work on the motion of bodies. He also completes his theory of colors, develops the main ideas on the calculus, and his law of gravitation.

1668

Isaac Newton designs and builds a reflecting telescope.

1672

Isaac Newton, in a letter to the Royal Society, describes his experiments explaining the nature of color. This letter became Newton’s first published scientific paper.

1676

Robert Hooke proposes his law relating the elongation of a spring to the force applied to produce that elongation.

1714

Gabriel Fahrenheit introduces the mercury thermometer and his new scale of temperature.

1738

Daniel Bernoulli develops the foundations of hydrodynamics.

1742

Anders Celsius proposes a new temperature scale.

1838

Friedrich Bessel first observes the parallax of a star with the aid of a telescope.

1747

Benjamin Franklin conducts experiments that show that one type of electrification could be neutralized by the other type. This indicated to him that the two types of electricity were not just different; they were opposites and calls one type positive and the other negative.

1848

William Thomson, Lord Kelvin, devises what is now known as the absolute temperature scale or Kelvin scale.

1766

Joseph Priestley proposes that the force between electric charges follows an inverse square law.

1777

Charles de Coulomb invents a torsion balance to measure the force between electrically charged objects (Coulomb’s law).

1787

Jacques-Alexander Charles discovers the relationship between the change in volume of a gas with temperature. He fails to publish his discovery.

1798

Henry Cavendish adapts the torsion balance invented by Coulomb to measure the gravitational constant.

1798

Benjamin Thompson, Count Rumford, introduces the idea that the heat was a form of motion.

1800

Alessandro Volta invents the battery.

1802

Thomas Young, in a landmark experiment, demonstrates that light is a wave phenomenon.

1802

Gian Domenico Romagnosi proposes in a newspaper article that an electric current affects a magnetic current. His discovery is largely ignored. Oersted, a better known scientist, would discover the same phenomenon in 1819.

1804

Joseph Louis Gay-Lussac, without knowledge of Charles’ work of 1787, discovers the relationship between the expansion of a gas at constant pressure and the temperature. This discovery is known as Gay-Lussac’s law.

1808

John Dalton develops his atomic theory.

1814

Joseph von Fraunhofer invents the spectroscope and with it he observes the absorption lines in the sun's spectrum two years later.

1819

Hans Christian Oersted discovers that an electric current deflects a magnetic compass. His discovery, published in a scientific journal, gets noticed.

1820

André Ampère gives mathematical form to Oersted’s discovery. In modern language, Ampère’s law is stated as follows: an electric current creates a magnetic field.

1820

Biot and Savart propose a force law between an electric current and a magnetic field.

1822

André Ampère shows that two wires carrying electric currents attract each other.

1827

Georg Ohm shows that current and voltage are related by a very simple relationship, known today as Ohm's law.

1831

Michael Faraday showed experimentally that a changing magnetic field produces an electric current (Faraday’s law).

1842

Christian Doppler proposes his Doppler Effect for sound and light waves.

1843

James Joule measures the electrical equivalent of heat.

1846

Gustav Kirchhoff proposes his rules of electrical circuits (Kirchoff's rules).

1850

Rudolf Gottlieb, known as Clausius, states the second law of thermodynamics.

1851

Armand Fizeau measures the velocity of light in a moving medium.

1868

James Clerk Maxwell proposes the electromagnetic nature of light and suggests that electromagnetic waves exist and are observed as light.

1869

Dmitri Mendeleyev proposes his periodic table of the chemical elements.

1873

Johannes van der Waals develops his theory of intermolecular forces in fluids.

1887

Heinrich Hertz generates electromagnetic waves in his laboratory.

1887

Albert Michelson and E.W. Morley, in a landmark experiment, determine the absence of the ether, a substance postulated to fill all space.

1895

Wilhelm Roentgen discovers X-rays.

1890

James Prescott Joule measures the mechanical equivalent of heat.

1897

J.J. Thomson determines the charge to mass ratio of the electron.

1898

Pierre and Marie Curie discover the radioactive elements radium and polonium.

1898

Ernest Rutherford discovers alpha and beta radiation.

1900

Max Planck introduces the concept of quanta in black body radiation and Planck’s constant.

1905

Albert Einstein explains Brownian motion.

1905

Albert Einstein explains the photoelectric effect.

1905

Albert Einstein publishes his special theory of relativity.

1905

Albert Einstein postulates the equivalence of mass and energy.

1906

Albert Einstein proposes quantum explanation of the specific heat laws for solids.

1909

Robert Millikan measures the charge on the electron.

1911

Heike Kamerlingh Onnes introduces his theory of superconductivity.

1911

Ernest Rutherford discovers the nucleus of the atom.

1913

Niels Bohr proposes his quantum theory of atomic orbits.

1915

Albert Einstein publishes his general theory of relativity.

1916

Karl Schwarzschild calculates the critical radius of curvature of space-time around a collapsing star at which light cannot escape.

1917

Albert Einstein presents his theory of stimulated emission, the foundation for the laser.

1918

Emmy Nöther proposes the mathematical relationships between symmetry and conservation laws of physics.

1923

Louis de Broglie predicts the wave nature of particles.

1925

Werner Heisenberrg develops matrix mechanics, the first quantum mechanical theory.

1926

Erwin Schrödinger develops wave mechanics, an alternate quantum mechanical theory.

1926

Werner Heisenberg proposes the uncertainty principle.

1927

Niels Bohr proposes the principle of complementarity.

1927

Niels Bohr develops the Copenhagen interpretation of quantum mechanics.

1930

Ernest Orlando Lawrence and M. Stanley Livingston invent the cyclotron.

1932

James Chadwick identifies the neutron.

1932

Werner Heisenberg proposes that the nucleus of an atom is composed of protons and neutrons.

1942

Enrico Fermi obtains the first self sustaining fission reaction.

1948

Shin’ichiro Tomonaga, Julian Schwinger, and Richard Feynman develop quantum electrodynamics or QED.

1948

John Bardeen, Walter Brattain, and William Shockley invent the transistor.

1953

Charles Townes invents the maser.

1954

C.N. Yang and Robert L. Mills propose a non-abelian gauge theory.

1956

Murray Gell-Mann and Kazuhiko Nishijima introduce the strangeness quantum number.

1957

John Bardeen, Leon Cooper, and John R. Schrieffer propose their BCS theory of superconductivity.

1961

Sheldon Glashow introduces the neutral intermediate vector boson of electroweak interactions.

1961

Murray Gell-Mann and Yuval Ne'eman independendently discover the SU(3) octet symmetry of hadrons.

1964

Peter Higgs, Robert Brout, and F. Englert introduce the Higgs mechanism of symmetry breaking.

1964

Murray Gell-Mann and George Zweig independently propose the quark theory of hadrons.

1965

John Stewart Bell states and proves a powerful theorem (Bell’s theorem), which gives the theoretical limits on the correlations between the results of simultaneous measurements done on two separated particles. The limits on these correlations are given by Bell in the form of an inequality.

1965

Arno Penzias and Robert Wilson measure the cosmic background radiation.

1967

Steven Weinberg and Abdus Salam independently propose the electroweak unification which is based on significant contributions by Sheldon Glashaw. The three would later share the Nobel Prize in physics for their theory.

1974

Howard Georgi and Sheldon Glashow propose the SU(5) as a Grand Unified Theory and predict decay of the proton.

1977

A Fermilab team detects the bottom quark

1981

Michael Green and John Schwarz propose what becomes known as Type I superstring theory.

1981

Gerd Binnig and Heinrich Rohrer invent the scanning tunneling microscope.

1982

Alain Aspect performs an experiment that is considered to confirm the non-local aspects of quantum mechanics.

1983

Carlo Rubbia leads a team that detects the W and Z bosons at CERN.

1994

A Fermilab team detects the top quark.

2000

Tantalizing hints of the existence of the Higgs boson are seen in experiments with the Large Electron Positron collider at CERN, the European Laboratory for Particle Physics.