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| 1895 |
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| Wilhelm K. Röntgen (1845–1923) announced the discovery of x-rays in Eine neue Art von Strahlen. | 1 |
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| 1895 |
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| John W. Strutt (Lord Rayleigh) (1842–1919) and William Ramsay (1852–1916) discovered the “inert” or “noble” gas argon. Ramsay later discovered the other noble gases: helium, krypton, neon, xenon, and radon. | 2 |
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| 1895 |
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| Henri Poincaré (1854–1912) founded algebraic topology. He first applied topology to celestial mechanics (1892–99). | 3 |
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| 1896 |
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| Alfred B. Nobel (1833–96) endowed prizes for outstanding achievements in physics, chemistry, medicine, and physiology. The first prizes were awarded in 1901, to Wilhelm K. Röntgen in physics, Jacobus H. van't Hoff (1852–1911) in chemistry, and Emil A. von Behring (1854–1917) in medicine and physiology. | 4 |
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| 1896 |
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| Antoine H. Becquerel (1852–1908) discovered radioactivity in uranium compounds. | 5 |
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| 1897 |
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| Joseph John Thomson (1856–1940) announced the discovery of the electron, the first subatomic particle, and determined experimentally the ratio of its mass to its charge. | 6 |
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| 1900 |
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| Max Planck (1858–1947) stated that energy is not emitted continuously from radiating bodies, but in discrete parcels, or quanta. | 7 |
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| 1902–4 |
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| Henri Lebesgue (1875–1941) gave a theory of measure and the Lebesgue integral, extending the notions of integration and area to more general sets. | 8 |
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| 1904 |
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| Marie Sklodowska Curie (1867–1934) showed that pitchblende (uranium ore) contained two new radioactive elements: radium and polonium. | 9 |
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| 1904 |
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| Ernst Zermelo (1871–1953) published a proof that every set can be well ordered, which made possible the use of transfinite methods in mathematics. | 10 |
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| 1905 |
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| Albert Einstein (1879–1955) announced his special theory of relativity, which required a fundamental revision in the traditionally held Newtonian views of space and time, and introduced the celebrated equation E = mc2. | 11 |
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| 1905 |
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| Einstein attributed to radiation itself a particle structure, and by supposing each particle of light (photon) to carry a quantum of energy, explained the photoelectric effect. | 12 |
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