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1632: Galileo Galilei introduced his Galilean relativity which states that the fundamental laws of physics are the same in all inertial frames. Galileo gave the example of a ship travelling at constant velocity, without rocking, on a smooth sea; any observer doing experiments below the deck would not be able to tell whether the ship was moving or stationary.
1687: Sir Isaac Newton (1642 – 1727), English physicist: the originator of the Newton's Laws of Motion which were published in the Principia. Newton himself was not aware at the time that his laws were correct only for low speed moving objects.
1851: Hippolyte Fizeau (1819 – 1896), French physicist: The Fizeau experiment measured the relative speeds of light in moving water.
1861: James Clerk Maxwell (1831 – 1879), Scottish: the originator of Maxwell's equations - that predict the existence of a fixed speed of light, independent of the speed of the observer - that paved the way for Einstein's special theory of relativity.
1887: Albert Michelson (1852 – 1931) and Edward Morley (1838 – 1923): the Michelson–Morley Experiment proved that the ether is not a physical existing entity enabling Einstein later to postulate that there is no a natural rest or relative frame in the universe and that any measurement of the speed of light in any inertial frame will always give 186,300 miles per second..
1889: George FitzGerald (1851 – 1901), Irish: suggested the FitzGerald-Lorentz contraction - the decrease in length detected by an observer of objects that travel at any non-zero velocity is relative to that observer.
1895: Hendrik Antoon Lorentz (1853 – 1928), Dutch physicist: derived the transformation equations subsequently used by Albert Einstein to describe space and time (Special Theory of Relativity).
1905: Jules Henri Poincare (1854 – 1912), French mathematician: was the first to present the Lorentz transformations in their modern symmetrical form.
1905: Albert Einstein (1879 – 1955), German-American: In 1905 Einstein published his theory of special relativity stating that all uniform motion is relative and that there is no absolute state of rest. Einstein based his theory on two postulates: that physical laws are the same in all inertial reference systems, and the principle of the invariance of the speed of light, that the speed of light in a vacuum is a universal constant for all observers regardless of the motion of the observer or of the motion of the source of light. The consequence of special relativity is the equivalence of matter and energy - E = mc2
1907: Hermann Minkowski (1864 – 1909), German mathematician: introdued the Minkowski spacetime" - a four dimensional space including time - by which Einstein's special relativity could be best understood.
1911: Paul Langevin (1872 – 1946), French physicist: suggested the twin paradox
1915: Albert Einstein (1879 – 1955), German-American: Einstein expanded his Special Theory of Relativity into the General Theory of Relativity that applies also to systems in nonuniform accelerated motion. In other words, it included the effect of gravitation on the shape of space and the flow of time (Einstein's equations).
1948: Howard Percy Robertson (1903 – 1961), American physicist: invented a test theory that will prove the validity of Special Theory of Relativity.
General Relativity Milestones
1609: Johannes Kepler (1571 – 1630), German astronomer: formulated Kepler's laws of planetary motion that set the scene for Newton's theory of universal gravitation.
1634: Galileo Galilei (1564 – 1642), Italian physicist: Galileo's understanding of the motions on an inclined plane and falling bodies paved the way for Newton's theory of gravity.
1687: Sir Isaac Newton (1642 – 1727), English physicist: Newton's law of universal gravitation was published in the Principia by which gravity is the result of an attractive force between massive objects but although even Newton was bothered by the unknown nature of this force.
1798: Henry Cavendish (1731 – 1810), British: measured the Earth's density and the result was later used to calculate gravitational constant (G).
1854: Bernhard Riemann (1826 – 1866), German mathematician: founded Riemannian geometry enabling the later development of general relativity by Einstein.
1885: Lorand Eotvos (1848 – 1919), Hungarian physicist: cnducted the Eötvös experiment that measured the correlation between inertial mass and gravitational mass, demonstrating that the two were one and the same (equivalence principle).
1905: Albert Einstein (1879 – 1955), German-American: his theory of special relativity expanded Newton's low speed laws of motion to high speed (near the speed of light) not accelerated moving objects. In other words, at this stage Einstein restricted his theory to non-gravitational motion.
1915: Albert Einstein (1879 – 1955), German-American: he expanded his Special Theory of Relativity into the General Theory of Relativity that applies also to systems in nonuniform accelerated motion (gravitational motion). In other words it included the effect of gravitation on the shape of space and the flow of time (Einstein's equations).
1915: David Hilbert (1862 – 1943), German mathematician: submitted an article containing the correct field equations for general relativity five days before Einstein. Hilbert never claimed priority for this theory (the matter is disputed).
1915: Karl Schwarzschild (1873 – 1916), German physicist: provided the first exact solution to the Einstein field equations of general relativity for the limited case of a single spherical non-rotating mass (Schwarzschild solution). It describes spacetime in the vicinity of a non-rotating massive spherically-symmetric object.
1919: Arthur Eddington (1882 – 1944), British astrophysicist: confirmed general relativity's prediction for the deflection of starlight by the Sun during a total solar eclipse.
1922: Alexander Friedman (1888 – 1925), Russian physicist and mathematician: derived from Einstein's general relativity field equations that the universe is expanding.
1929: Edwin Hubble (1889 – 1953), American astronomer: found evidence for the idea that the universe is expanding (redshift) and this evidence is consistent with the solutions of Einstein’s equations of general relativity (Alexander Friedman).
1960: Martin Kruskal (1925 – 2006), American mathematician and physicist: discovered the full classical spacetime structure of the simplest type of a black hole in General Relativity.
1974: Stephen Hawking (1942 - ), English theoretical physicist: developed theoretical prediction that black holes should emit radiation (Hawking radiation).