German physicist Arnold Sommerfeld died #OTD in 1951.
In 1916, he introduced the idea of elliptical orbits for electrons, and he also introduced additional quantum numbers which included the azimuthal quantum number and magnetic quantum number. He also introduced a dimensionless physical constant known as the fine-structure constant. This constant characterizes the strength of the electromagnetic interaction between elementary charged particles.
Here is a curious finding from our statistical analysis https://arxiv.org/abs/2403.16217 :
A #Feynmangraph is a graphical short hand notation for a complicated integral that computes the probability for scattering processes in #quantum field theory.
An electrical circuit can also be described as a graph. What happens if we interpret the Feynman graph as an #electrical network, where each edge is a 1 Ohm resistor? We can then compute the resistance between any pair of vertices and collect all these values in a "resistance matrix", as shown below. The average of all these resistances is called "Kirchhoff index". Now it turns out that this average resistance is correlated fairly strongly with the Feynman integral of that graph: A graph with large contribution to quantum scattering amplitudes on average also has a large electrical resistance. Isn't that a nice connection between two seemingly distinct branches of theoretical #physics ?
French mathematician and physicist Siméon-Denis Poisson died #OTD in 1840.
He is known for his significant contributions to mathematical physics, particularly in the fields of mechanics, probability theory, and electricity. He made crucial advancements in understanding the behavior of fluids & the mathematical treatment of physical phenomena. Some of his most notable contributions include: Poisson distribution, potential theory, fluid mechanics, electromagnetism.
Swedish astronomer, physicist, and mathematician Anders Celsius died #OTD in 1744.
In 1742, Celsius introduced the temperature scale that bears his name. His original scale was actually the reverse of what we use today: it set the boiling point of water at 0 degrees & the freezing point at 100 degrees. However, shortly after his death, the scale was reversed by Carl Linnaeus, resulting in the 0 degrees for freezing & 100 degrees for boiling that we are familiar with.
The idea that matter is mostly empty space is mostly wrong.
From Big Think: "Practically all of the matter we see and interact with is made of atoms, which are mostly empty space. Then why is reality so... solid?"
German physicist Max Planck was born #OTD in 1858.
Planck made many substantial contributions to theoretical physics, specially as the originator of quantum theory, which revolutionized understanding of atomic and subatomic processes. He is known for Planck's constant, which is of foundational importance for quantum physics, and which he used to derive a set of units (Planck units) expressed only in terms of fundamental physical constants.
"I regard consciousness as fundamental. I regard matter as derivative from consciousness. We cannot get behind consciousness. Everything that we talk about, everything that we regard as existing, postulates consciousness."
Interview in 'The Observer' (25 January 1931), p.17, column 3
It was 100 years ago when Max Planck published a paper that gave birth to quantum mechanics – or so the story goes. History reveals, however, that Planck did not immediately realize the consequences of his work and became a revolutionary against his will. via @PhysicsWorld
Where (in England) do they sell physical copies of mathematics and physics textbooks that you can pick up and peruse before buying?
The obvious answer is Foyles on Charing Cross Road, but lately the selection of maths & physics textbooks there has been pitiful. They're barely bothering to stock textbooks any more (it didn't look much better for the adjacent chemistry and biology sections either), and lately when I've gone, it's not sated my need to physically shop for textbooks.
Died #OTD in 1989. Emilio Segrè was an Italian and naturalized-American physicist who discovered the elements technetium and astatine, & the antiproton, a subatomic antiparticle, for which he was awarded the Nobel Prize in Physics in 1959 along with Owen Chamberlain.
Together with Glenn T. Seaborg, he discovered technetium-99m—the first artificially produced element (1937). Tc99m is first element found to have no stable isotopes, filling a missing spot on the periodic table.
British Geologist And Astronomer John Michell died #OTD in 1793.
He is the first person known to have proposed the existence of stellar bodies comparable to black holes, and the first to have suggested that earthquakes travelled in (seismic) waves. He invented an apparatus to measure the mass of the Earth, and explained how to manufacture an artificial magnet.
He and Marie Curie, along with Henri Becquerel, were awarded the Nobel Prize in Physics in 1903 for their joint research on radiation phenomena. In 1898, he isolated the radioactive elements polonium and radium from pitchblende ore, a significant achievement that helped expand the understanding of the nature of radioactive decay. He tragically died in a street accident.
“On peut se demander si l'humanité a avantage à connaître les secrets de la nature, si elle est mure pour en profiter ou si cette connaissance ne sera pas nuisible.”
"It's debatable whether mankind benefits from knowing nature's secrets, whether it's ripe for profit, or whether such knowledge will be harmful."