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François Levrier

@francoislevrier.bsky.social

110 followers 140 following 260 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 · 11h

Asaph Hall was born #OTD in 1829. An American astronomer, he discovered the two satellites of Mars over the course of a single week : Deimos on August 12, 1877 and Phobos just six days later.
en.wikipedia.org/wiki/Asaph_H...

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François Levrier @francoislevrier.bsky.social · 11h

Evangelista Torricelli was born #OTD in 1608. A student of Galileo, he is credited with inventing the barometer, although some evidence suggests that Gasparo Berti may have designed a similar device a few years earlier.
en.wikipedia.org/wiki/Evangel...

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François Levrier @francoislevrier.bsky.social · 1d

He was the original very stable genius.

François Levrier @francoislevrier.bsky.social · 1d

Joseph Plateau was born #OTD in 1801. A Belgian physicist and mathematician, he worked in optics, inventing an early stroboscopic device, and surface tension problems. Plateau’s laws describe the structure of soap films.
en.wikipedia.org/wiki/Joseph_...

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François Levrier @francoislevrier.bsky.social · 2d

Peter Barlow was born #OTD in 1776. An English mathematician and physicist, he designed an achromatic doublet lens to increase the focal length of telescopes. Barlow's wheel is an early homopolar electric motor.
en.wikipedia.org/wiki/Peter_B...

François Levrier @francoislevrier.bsky.social · 4d

Heinrich Olbers was born #OTD in 1758. His name is usually associated with the famous "paradox" of the night sky's darkness, but he is also the discoverer of two of the largest asteroids, Pallas and Vesta.
en.wikipedia.org/wiki/Heinric...

François Levrier @francoislevrier.bsky.social · 5d

A noted chemist, he also identified hydrogen (dubbed « inflammable air ») and worked out the composition of ordinary air (four parts nitrogen for one part oxygen, plus a residue later identified as argon).

François Levrier @francoislevrier.bsky.social · 5d

Henry Cavendish was born #OTD in 1731. A very careful experimentalist, he is mostly known for the experiment to determine the Earth’s density, using a torsion balance. He obtained a value within 1% of the currently accepted figure.
en.wikipedia.org/wiki/Henry_C...

François Levrier @francoislevrier.bsky.social · 6d

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

François Levrier @francoislevrier.bsky.social · 6d

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 · 7d

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 · 8d

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 · 8d

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 · 9d

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 · 10d

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 · 11d

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 · 14d

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 · 14d

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 · 15d

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 · 15d

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 · 16d

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 · 16d

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 · 16d

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 · 17d

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 · 18d

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_...