iiinova — where your digital self keeps evolving

François Levrier @francoislevrier.bsky.social · 10h

The Zeeman effect is used in astrophysics to measure the magnetic field intensity along the line of sight, taking advantage of the opposite circular polarizations of the sigma components.

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François Levrier @francoislevrier.bsky.social · 10h

Pieter Zeeman died #OTD in 1943. The effect that bears his name, and for which he received the 1902 Nobel Prize in Physics with H. Lorentz, is the splitting of spectral lines by a static magnetic field. en.wikipedia.org/wiki/Pieter_...

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François Levrier @francoislevrier.bsky.social · 10h

Karl’s son Martin was a brilliant German-American astrophysicist in his own right, working on stellar structure and evolution.

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François Levrier @francoislevrier.bsky.social · 10h

Karl Schwarzschild was born #OTD in 1873. While in the German Army on the Russian front, he worked out the first exact solution to Einstein’s General Relativity, describing space-time near non-rotating spherical objects. en.wikipedia.org/wiki/Karl_Sc...

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François Levrier @francoislevrier.bsky.social · 08/10/2026

Jacob Robert Emden died #OTD in 1940. A Swiss astrophysicist and meteorologist, he developed the theory of gaseous spheres in equilibrium between gravity and pressure that is used in studies of stellar structure, white dwarfs, and prestellar cores. en.wikipedia.org/wiki/Robert_...

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François Levrier @francoislevrier.bsky.social · 08/10/2026

Ejnar Hertzsprung was born #OTD in 1873. With H. Russell, he devised the diagram that bears their names, where stars are plotted as a function of their colors and luminosities, a major step towards understanding stellar evolution. en.wikipedia.org/wiki/Ejnar_H...

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François Levrier @francoislevrier.bsky.social · 07/10/2026

This supernova remnant is wow ! science.nasa.gov/image-articl...

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François Levrier @francoislevrier.bsky.social · 07/10/2026

Gérard de Vaucouleurs died #OTD in 1995. A French astronomer who did most of his career in the USA, he was a co-author of the Third Reference Catalogue of Bright Galaxies with his wife Antoinette. en.wikipedia.org/wiki/G%C3%A9...

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François Levrier @francoislevrier.bsky.social · 07/10/2026

George Ogden Abell died #OTD in 1983. An American astronomer, his work on the Palomar Sky Survey led to the publication of a catalogue of over 2700 galaxy clusters, and another catalogue of planetary nebulæ, containing 86. en.wikipedia.org/wiki/George_...

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François Levrier @francoislevrier.bsky.social · 07/10/2026

Niels Bohr was born #OTD in 1885. One of the pioneers of quantum physics, his debates with Einstein regarding the fundamentally non-local nature of the new physics were central to our understanding of the physical world. en.wikipedia.org/wiki/Niels_B...

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François Levrier @francoislevrier.bsky.social · 06/10/2026

Balthasar van der Pol died #OTD in 1959. A Dutch physicist, he developed an analysis of coupled differential equations in electrical systems, leading to the Van der Pol oscillator, which includes a non-linear damping term. en.wikipedia.org/wiki/Balthas...

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François Levrier @francoislevrier.bsky.social · 06/10/2026

Meghnad Saha was born #OTD in 1893. An Indian astrophysicist whose study of thermal ionization led him to formulate the equation that bears his name, relating the populations of various ionization stages at thermal equilibrium. en.wikipedia.org/wiki/Meghnad...

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François Levrier @francoislevrier.bsky.social · 05/10/2026

Dorothea Klumpke died #OTD in 1942. Although American-born, she studied astronomy in Paris, eventually heading the « Bureau des Mesures » of the Observatory, in charge of the « Carte du ciel » international project. en.wikipedia.org/wiki/Dorothe...

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François Levrier @francoislevrier.bsky.social · 05/10/2026

Lars Onsager died #OTD in 1976. The Onsager relations put constraints on the linear response (e.g., heat flux) to imbalances in thermodynamic properties. He also provided the analytic solution to the 2D Ising model in zero field. en.wikipedia.org/wiki/Lars_On...

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François Levrier @francoislevrier.bsky.social · 05/10/2026

Robert Hutchings Goddard was born #OTD in 1882. He built the first liquid-fuel rocket, launched in 1926, which makes him one of the pioneers of rocket physics and space travel, alongside Esnault-Pelterie, Tsiolkovsky, and Oberth. en.wikipedia.org/wiki/Robert_...

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François Levrier @francoislevrier.bsky.social · 04/10/2026

Léon Brillouin died #OTD in 1969. A pioneer of solid-state physics, he studied the interaction of light with matter. He emigrated to the USA in 1940, occupying several positions and exploring the topics of information theory. en.wikipedia.org/wiki/L%C3%A9...

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François Levrier @francoislevrier.bsky.social · 04/10/2026

Max Planck died #OTD in 1947. His postulate that electromagnetic radiation is quantized, introducing the constant that bears his name, is widely acknowledged as marking the birth of quantum theory. en.wikipedia.org/wiki/Max_Pla...

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François Levrier @francoislevrier.bsky.social · 04/10/2026

Vitaly Ginzburg was born #OTD in 1916. A Russian theoretical physicist known for a phenomenological theory of superconductivity. He also demonstrated the production of EM radiation when a charge moves in heterogeneous media. en.wikipedia.org/wiki/Vitaly_...

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François Levrier @francoislevrier.bsky.social · 03/10/2026

Leon Lederman died #OTD in 2018. With Garwin and Heinrich, he verified parity violation independently from Wu. Later on, he discovered the muon neutrino, for which he received the 1988 Nobel prize, and the bottom quark. en.wikipedia.org/wiki/Leon_M....

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François Levrier @francoislevrier.bsky.social · 02/10/2026

He made a connection between CO2 level in the air and temperature. Not a model of global warming per se, but a first step : www.jstor.org/stable/4314543

jstor.org

Client Challenge

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François Levrier @francoislevrier.bsky.social · 02/10/2026

Svante Arrhenius died #OTD in 1927. One of the founders of physical chemistry, he gave the first modern definition of acids and bases. The Arrhenius equation describes reaction rates, introducing the concept of activation energy. en.wikipedia.org/wiki/Svante_...

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François Levrier @francoislevrier.bsky.social · 01/10/2026

In the Manhattan project, he determined the amount of enriched U to achieve criticality. The experiments often came a little too close to the critical mass, or even above it for a fraction of a second, a process Feynman called « tickling the tail of a sleeping dragon ».

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François Levrier @francoislevrier.bsky.social · 01/10/2026

Otto Frisch was born #OTD in 1904. An Austrian-born British physicist, he and his aunt Lise Meitner explained the process of nuclear fission observed by Hahn and Strassmann. He outlined the process for producing an atomic bomb. en.wikipedia.org/wiki/Otto_Ro...

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François Levrier @francoislevrier.bsky.social · 30/09/2026

Charles Francis Richter died #OTD in 1985. His childhood interest in astronomy led him to call « magnitude » the intensity of earthquakes that the scale which bears his name measures. en.wikipedia.org/wiki/Charles...

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François Levrier @francoislevrier.bsky.social · 30/09/2026

Jean Perrin was born #OTD in 1870. Famous for experiments on Brownian motion, he was also a major advocate for the advancement of science, leading to the creation of Observatoire de Haute-Provence, Palais de la Découverte, and CNRS. en.wikipedia.org/wiki/Jean_Ba...

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François Levrier @francoislevrier.bsky.social · 29/09/2026

Fermi was also famous for his back-of-the-envelope calculations, now called « Fermi problems », one of which was... estimating the number of piano tuners in the Chicago area.

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François Levrier @francoislevrier.bsky.social · 29/09/2026

Fermi-Dirac statistics apply to particles, called fermions, obeying Pauli’s exclusion principle, while the « golden rule » gives the transition rate between quantum states under a perturbation.

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François Levrier @francoislevrier.bsky.social · 29/09/2026

Enrico Fermi was born #OTD in 1901. An Italian-born American physicist who received the 1938 Nobel Prize for induced radioactivity. He was a pioneer of the atomic age, demonstrating the first self-sustaining nuclear chain in 1942. en.wikipedia.org/wiki/Enrico_...

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François Levrier @francoislevrier.bsky.social · 28/09/2026

Martin David Kruskal was born #OTD in 1925. A mathematician and physicist, he made vast contributions to the study of instabilities in plasmas, to general relativity, and to solitary wave (« soliton ») phenomena. en.wikipedia.org/wiki/Martin_...

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François Levrier @francoislevrier.bsky.social · 27/09/2026

Do you have 17 hours of spare time ? They would be very well spent on this "Particle Physics Marathon" by Kamil Laurent. An excellent introduction to the topic if you have basic knowledge of quantum physics and Lagrangian mechanics. youtu.be/YFiQIZOM2fw?...

youtu.be

Particle Physics in 17 Hours

YouTube video by Kamil Laurent

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François Levrier @francoislevrier.bsky.social · 27/09/2026

Martin Ryle was born #OTD in 1918. In the aftermath of WWII, he was a pioneer of interferometry and aperture synthesis in radio astronomy with the Cambridge group. For this he received the 1974 Nobel Prize in Physics. en.wikipedia.org/wiki/Martin_...

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François Levrier @francoislevrier.bsky.social · 26/09/2026

Les bénévoles de l'association remettent en état ces matériels et les exposent régulièrement pour montrer les principes de la diffusion et de la réception de l'information, comme avec ce cohéreur de Branly en action. Merci à eux pour cette journée.

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François Levrier @francoislevrier.bsky.social · 26/09/2026

Au détour d'une étagère, on retrouve des ouvrages et des objets qui pourront rappeler à certains des souvenirs d'agrégation de physique, plus ou moins lointains.

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François Levrier @francoislevrier.bsky.social · 26/09/2026

Au travers de legs de particuliers ou d'entreprises, l'ACHDR préserve la mémoire technique des matériels de la radio et de la télévision françaises.

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François Levrier @francoislevrier.bsky.social · 26/09/2026

À l'occasion de ses 35 ans, l'association du centre historique de la diffusion radiophonique d'Issoudun a rendu hommage à mon père, Philippe Levrier, en donnant son nom à leur salle d'exposition, au sein du bâtiment de TDF dont il avait empêché la destruction.

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François Levrier @francoislevrier.bsky.social · 25/09/2026

In his final years, he suffered from depression and eventually killed himself in 1933, after fatally shooting his younger son, who had Down syndrome. His mentor, Ludwig Boltzmann, had also committed suicide in 1906.

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François Levrier @francoislevrier.bsky.social · 25/09/2026

He held a professor position in Leiden, where he was widely regarded as an extraordinary teacher and mentor. He was a close friend of Einstein’s, whom he invited regularly in Leiden.

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François Levrier @francoislevrier.bsky.social · 25/09/2026

Paul Ehrenfest died #OTD in 1933. An Austrian physicist, he made vast contributions to statistical mechanics and quantum physics. The Ehrenfest theorem states that expectation values of quantum operators behave classically. en.wikipedia.org/wiki/Paul_Eh...

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François Levrier @francoislevrier.bsky.social · 25/09/2026

Johann Heinrich Lambert died #OTD in 1777. A Swiss mathematician and physicist who made important contributions to optics, such as the Beer-Lambert law of attenuation, he also was a pioneer of map projections. en.wikipedia.org/wiki/Johann_...

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François Levrier @francoislevrier.bsky.social · 25/09/2026

Ole Rømer was born #OTD in 1644. He timed Io’s eclipses in Jupiter’s shadow from different points on the Earth’s orbit, allowing Huygens and others to determine a value of approximately 212000 km/s for the speed of light. en.wikipedia.org/wiki/Ole_R%C...

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François Levrier @francoislevrier.bsky.social · 24/09/2026

After making contributions to relativity theory, he turned to music theory during WWII, building a novel 31-tone microtonal organ.

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François Levrier @francoislevrier.bsky.social · 24/09/2026

Adriaan Fokker died #OTD in 1972. A Dutch physicist and cousin of aircraft manufacturer Anthony Fokker, he co-derived the Fokker-Planck equation describing the time evolution of distributions of particles under drag and diffusion. en.wikipedia.org/wiki/Adriaan...

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François Levrier @francoislevrier.bsky.social · 24/09/2026

Charlotte Moore Sitterly was born #OTD in 1898. She worked extensively on the chemical composition of the Sun, based on spectroscopic data. In particular, she identified technetium, providing the first naturally occurring detection of that element. en.wikipedia.org/wiki/Charlot...

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François Levrier @francoislevrier.bsky.social · 23/09/2026

Charles K. Kao died #OTD in 2018. His work on optical fibers proved that attenuation could be significantly reduced by using high-purity fused silica, opening the path to the wide use of this technology in modern communications. en.wikipedia.org/wiki/Charles...

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François Levrier @francoislevrier.bsky.social · 23/09/2026

Urbain Le Verrier died #OTD in 1877. He predicted the existence of Neptune in 1846 from the perturbation of the orbit of Uranus. Adams made the same computation independently, and Galle was the first to observe the planet. en.wikipedia.org/wiki/Urbain_...

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François Levrier @francoislevrier.bsky.social · 23/09/2026

Hippolyte Fizeau was born #OTD in 1819. Working together with L. Foucault, and then as his rival, he determined the speed of light in air to within five percent, improving on Rømer’s much earlier determination. en.wikipedia.org/wiki/Hippoly...

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François Levrier @francoislevrier.bsky.social · 22/09/2026

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François Levrier @francoislevrier.bsky.social · 22/09/2026

Otto Frisch died #OTD in 1979. An Austrian-born British physicist, he and his aunt Lise Meitner explained the process of nuclear fission observed by Hahn and Strassmann. He outlined the process for producing an atomic bomb. en.wikipedia.org/wiki/Otto_Ro...

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François Levrier @francoislevrier.bsky.social · 22/09/2026

Frederick Soddy died #OTD in 1956. With Rutherford, he showed that radioactivity is associated with the transmutation of chemical elements. He received the 1921 Nobel Prize in Chemistry for his work on isotopes. en.wikipedia.org/wiki/Frederi...

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François Levrier @francoislevrier.bsky.social · 22/09/2026

Michael Faraday was born #OTD in 1791. Arguably one of the most brilliant experimental physicists in history, his work on the relationship between magnetism, electricity, and light laid the path for Maxwell’s electromagnetic theory. en.wikipedia.org/wiki/Michael...

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