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Einstein, Ehrenfest, and De Sitter; Eddington and Lorentz gathered in W. de Sitter's office in Leiden, Netherlands, on September 26, 1923.

Use "entropy" and you can never lose a debate, von Neumann told Shannon - because no one really knows what "entropy" is. -- William Poundstone

Sir Isaac Newton as a divine geometer created by William Blake in 1795.

World’s Most Iconic Graduate School Recommendation Letter ✍️

Sir Isaac Newton's handwritten Trinity college notes put together between 1661-1665 while he was an undergraduate student at that same college. Page one reads, “Not fit to be printed. 25 Sep 1727” written by Thomas Pellet. 📷 Cambridge, Trinity College

Feynman on the state of "confusion" ✍️ When you're thinking about something that you don't understand, you have a terrible, uncomfortable feeling called confusion. It's a very difficult and unhappy business. And so most of the time you're rather unhappy, actually, with this confusion. You can't penetrate this thing. Now, is the confusion's because we're all some kind of apes that are kind of stupid working against this, trying to figure out how to put the two sticks together to reach the banana and we can't quite make it, the idea? And I get this feeling all the time that I'm an ape trying to put two sticks together, so I always feel stupid. Once in a while, though, the sticks go together on me and I reach the banana. 📷 Caltech Archives Image

Riemann's housekeeper burned the papers, and what survived was seventy years ahead of everyone ✍️ Riemann died in 1866 and his housekeeper burned much of what he left behind. What escaped went to Göttingen as the Nachlass, 52 compilations of manuscripts, calculation sheets and drafts. The famous 1859 paper on prime numbers is eight pages long and states results without proof, which led Landau and Hardy in the early 1900s to complain that Riemann had conjectured much and proved almost nothing. Then in the early 1930s Carl Ludwig Siegel spent about two years deciphering the surviving scraps. He found that Riemann had proved much of what the paper merely asserted, and worse, had developed things nobody had rediscovered in seventy years. Hardy and Littlewood had recently derived an approximate functional equation for the zeta function and obtained only the dominant term; Riemann had the same formula and a method for estimating the remainder. Siegel published in 1932, and the result, now the Riemann–Siegel formula, went straight into current research rather than into the history books. It is still the standard tool for computing zeta zeros at large height. Riemann had also hand-calculated the first several zeros. The uncomfortable implication is that we have no idea how much was in the part that burned.

Planck introduced the quantum as a trick he did not believe ✍️ On 14 December 1900 Max Planck presented the derivation of his radiation law to the German Physical Society, and with it the constant h. The popular story says he did this to escape the "ultraviolet catastrophe" and quantised the energy of oscillators. Neither is quite right. Rayleigh's classical result played no real part in his reasoning; what drove him was the experimental data, in particular Rubens telling him on 7 October 1900 that the classical formula fitted only at long wavelengths. To derive the law he needed Boltzmann's statistical entropy, and to use it he had to count the ways energy could be shared among oscillators, so he divided the total energy into finite elements purely to make the counting possible. He expected, like Boltzmann before him, that the elements were a mathematical device. In an unpublished 1931 letter to the American physicist R. W. Wood, now held at the American Institute of Physics, he called it an act of desperation and a purely formal assumption to which he gave little thought beyond getting a positive result at any cost. For years afterward he tried to reconcile h with classical physics. It was Einstein in 1905, not Planck, who took the quanta literally.

Albert Einstein's letter to Maria Skłodowska Curie, 1911: Prague, 23 November 1911 Highly esteemed Mrs. Curie Do not laugh at me for writing you without having anything sensible to say. But I am so enraged by the base manner in which the public is presently daring to concern itself with you that I absolutely must give vent to this feeling. However, I am convinced that you consistently despise this rabble, whether it obsequiously lavishes respect on you or whether it attempts to satiate its lust for sensationalism! I am impelled to tell you how much I have come to admire your intellect, your drive, and your honesty, and that I consider myself lucky to have made your personal acquaintance in Brussels. Anyone who does not number among these reptiles is certainly happy, now as before, that we have such personages among us as you, and Langevinil too, real people with whom one feels privileged to be in contact. If the rabble continues to occupy itself with you, then simply don't read that hogwash, but rather leave it to the reptile for whom it has been fabricated. With most amicable regards to you, Langevin, and Perrin, yours very truly, A. Einstein P.S. I have determined the statistical law of motion of the diatomic molecule in Planck's radiation field by means of a comical witticism, naturally under the constraint that the structure's motion follows the laws of standard mechanics. My hope that this law is valid in reality is very small, though.

Notebook of Leonardo da Vinci, The Codex Arundel 📑 A collection of papers written in Italian by Leonardo da Vinci (b. 1452, d. 1519), in his characteristic left-handed mirror-writing (reading from right to left), including diagrams, drawings and brief texts, covering a broad range of topics in science and art, as well as personal notes. It's available online for free at the British Library online portal.

Schrödinger’s cat is not a real experiment, but a thought experiment, which means it is only imagined and not actually performed. Erwin Schrödinger came up with it to show the absurdity of applying quantum mechanics to everyday objects, such as cats. He did not intend to suggest that cats can be both alive and dead at the same time.

An article about Nikola Tesla titled, “M: Tesla Explains Why He Will Never Marry” published in. Galveston Daily News, p. 23, ca. 1924.

Today, September 23, 2026, marks the September Equinox at 00:06 UTC, when the Sun crosses directly above Earth's equator, making day and night nearly equal worldwide. It marks the start of astronomical autumn in the Northern Hemisphere and spring in the Southern Hemisphere.

Aryabhatta wrote his most famous treatise, Aryabhatiya, when he was only 23 years old. It contains 121 verses on various topics of mathematics and astronomy, such as the value of pi, the solution of quadratic equations, the calculation of eclipses, and the motion of planets.

Neptune was the first planet to be discovered by mathematical prediction rather than direct observation. The planet was discovered on the night of September 23-24, 1846, by German astronomer Johann Gottfried Galle at the Berlin Observatory. He was following the calculations of French astronomer Urbain Le Verrier, who had predicted the position of Neptune based on the irregularities in the orbit of Uranus.

Richard Feynman, the renowned physicist, also explored his artistic side under the pseudonym "Ofey," creating numerous drawings and paintings. His artistic work was not just a hobby but a significant aspect of his multifaceted genius.

The genius of John von Neumann 🧠 He could speak eight languages by the age of six, including Ancient Greek and Latin. He could divide eight-digit numbers in his head at the age of six. He was familiar with differential and integral calculus by the age of eight. He entered the University of Budapest at the age of 15 and earned a degree in chemical engineering at the age of 19. He obtained his Ph.D. in mathematics from the University of Berlin at the age of 22. John von Neumann was a remarkable mathematician, physicist, and computer scientist who was born in Hungary in 1903. He was a child prodigy who showed extraordinary talents in language, memory, and calculation. He made major contributions to many fields of mathematics, physics, economics, and computer science, such as game theory, quantum mechanics, operator algebras, von Neumann architecture, and cellular automata. v. Neumann was a genius who amazed his peers and influenced many disciplines. He is widely regarded as one of the greatest mathematicians of the 20th century.

Mathematics is not about numbers, equations, computations, or algorithms: it is about understanding. - Bill Thurston

Some important equations in Physics ✍️