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François Levrier

@francoislevrier.bsky.social

110 followers 140 following 250 posts

Professeur d’astrophysique - ENS Paris - Responsable du Master AAIS - Coordinateur de l’action thématique PCMI (Physique et Chimie du Milieu Interstellaire) (Photo ©A. Vergallo)

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François Levrier @francoislevrier.bsky.social · Jan 21

Keep up to date on the advances of the PCMI community towards understanding the physics and chemistry of the interstellar medium, with the presentations made at our 2024 conference, now online on Youtube.

www.youtube.com/playlist?lis...

Colloque 2024 du Programme PCMI (Bordeaux, 28-31 octobre 2024) - YouTube

www.youtube.com

François Levrier @francoislevrier.bsky.social · 16h

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...

François Levrier @francoislevrier.bsky.social · 1d

The experiments on quantum entanglement performed by A. Aspect and others in the last quarter of the 20th century finally proved Bohr right. Unless signals should travel at many times the speed of light, entangled quantum systems are indeed non-local.

François Levrier @francoislevrier.bsky.social · 1d

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 · 2d

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...

François Levrier @francoislevrier.bsky.social · 3d

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_...

François Levrier @francoislevrier.bsky.social · 4d

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_...

François Levrier @francoislevrier.bsky.social · 7d

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 ».

François Levrier @francoislevrier.bsky.social · 7d

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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Reposted by François Levrier

Institut d'astrophysique de Paris @iap.fr · 8d

He was also the founder of @iap.fr read more: www.iap.fr/institut/his...

A photo of the Institut d'astrophysique de Paris building, in Paris.

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François Levrier @francoislevrier.bsky.social · 8d

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...

François Levrier @francoislevrier.bsky.social · 9d

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.

François Levrier @francoislevrier.bsky.social · 9d

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.

François Levrier @francoislevrier.bsky.social · 9d

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 · 10d

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_...

François Levrier @francoislevrier.bsky.social · 11d

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_...

François Levrier @francoislevrier.bsky.social · 13d

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...

François Levrier @francoislevrier.bsky.social · 14d

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...

François Levrier @francoislevrier.bsky.social · 15d

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...

François Levrier @francoislevrier.bsky.social · 16d

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...

François Levrier @francoislevrier.bsky.social · 17d

Heike Kamerlingh Onnes was born #OTD in 1853. He received the 1913 Nobel Prize for his investigations of matter at very low temperatures, leading to the first liquefaction of helium and the discovery of superconductivity.
en.wikipedia.org/wiki/Heike_K...

François Levrier @francoislevrier.bsky.social · 18d

James Dewar was born #OTD in 1842. A British physicist and chemist, he invented a vacuum flask with which he was able to produce large quantities of liquid oxygen, that he then showed to be attracted by magnets.
en.wikipedia.org/wiki/James_D...

François Levrier @francoislevrier.bsky.social · 19d

Masatoshi Koshiba was born #OTD in 1926. He received the 2002 Nobel prize in Physics for pioneering work in neutrino astronomy, solving the solar neutrino problem by detecting evidence of neutrino oscillation with S-Kamiokande.
en.wikipedia.org/wiki/Masatos...

François Levrier @francoislevrier.bsky.social · 20d

Léon Foucault was born #OTD in 1819. The Foucault pendulum’s oscillation plane appears to rotate due to Earth’s own rotation. Foucault’s currents occur when a conducting material is subjected to a varying magnetic field.
en.wikipedia.org/wiki/L%C3%A9...

François Levrier @francoislevrier.bsky.social · 22d

Le montage expérimental, fait par des étudiants préparant l’agrégation.

François Levrier @francoislevrier.bsky.social · 22d

Visualisation des aberrations géométriques et chromatiques d’une lentille simple. On voit bien les nappes sagittale et tangentielle, et l’influence d’un indice optique plus élevé dans le bleu que dans le rouge.

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