Aula Magna of the University of Padua. Albert Einstein, in Italy for a series of lectures, wanted to personally meet Gregorio Ricci Curbastro (from Lugo di Romagna), whose mathematics on differential calculus was a crucial support for the development of General Relativity.

Greek soldiers are at the gates of Ankara; they are stopped by Turkish forces commanded by General Mustafa Kemal (Ataturk); he will later succeed in pushing the Greeks back from Anatolia and will be acclaimed as a national hero; the sultanate will be abolished and Turkey will become a republic.

Russian physicist Alexander Friedmann solves Einstein’s equations and derives a variety of expanding and contracting cosmological models; he sends the solutions to Albert Einstein, who remains lukewarm and prefers his own static model.

American astronomer Heber Curtis, opposing Harlow Shapley during a public debate at the Smithsonian Institution in Washington, DC, argues that the spiral nebulae visible in the night sky are actually very distant galaxies like our own.

Marie Curie was invited to travel to the United States by an American journalist, Mary “Missy” Meloney; upon her arrival in the United States she was welcomed triumphantly, and raised funds of 150,000 dollars to purchase more radium for her research.

Tulsa, Oklahoma. A 19-year-old black man, Dick Rowland, is accused of making sexual advances toward a white woman in an elevator. He is arrested, and a thousand white citizens surround the police station to lynch him. Several armed African-Americans rush to the scene. A counteroffensive ensues against the Greenwood neighborhood, home to a black population, among the most emancipated and productive in the country. The neighborhood is razed, and ten thousand residents are forced to start over. Responsibilities are passed around for decades. Only a century later, exactly 100 years, on May 31, 2021, US President Joe Biden apologizes to Tulsa’s black community for what happened, completely reversing the meaning of that incident.

Nobel Prize in Physics to Albert Einstein for the photoelectric effect, and not for light quanta or relativity, at the investiture ceremony, in the official speech Einstein obviously speaks about Relativity, a theory considered very controversial

Mitsubishi Electric is founded in Japan

Nikola Tesla filed a patent for an airplane that took off vertically, adjusted its propellers, and flew horizontally. The patent was approved in 1927. This was the VTOL technology that would not be realized until several decades later.

New York. A truck bomb filled with metal fragments explodes outside the JP Morgan headquarters on Wall Street, Manhattan. Thirty-two passersby are killed and hundreds more injured. Authorities attribute the attack to anarchists, but for financiers, it merely fuels further panic.

The Thule Society becomes the National Socialist German Workers’ Party (NationalSozialistische Deutsche ArbaiterPartei, NSDAP) with three thousand members.

Douglas and Boeing build their first airplanes

Max Born correctly proposes that the square of the Schrödinger wave function, which is always a positive real number, gives the probability of finding the particle at that point at that time; Max Born works with Wolfgang Pauli and Werner Heisenberg, whose Uncertainty Principle strongly influences his discovery; Max Born is the grandfather of actress Olivia Newton-John

Niels Bohr, Werner Heisenberg, Erwin Schrödinger, P.A.M. Dirac, Felix Bloch, Max Plank, Albert Einstein, Louis De Broglie, Born Jordan Pauli: Quantum Mechanics is born, undoubtedly one of the greatest achievements of 20th-century physics; it explains many mysterious 19th-century phenomena such as spectral lines, the stability of atoms, chemical bonds, the strength and colors of materials, ferromagnetism, phase transitions, the color of hot bodies in equilibrium, blackbody radiation, the reliability of hereditary characteristics (via DNA), but also phenomena discovered only in the 20th century such as liquid crystals, superconductivity, superfluidity, the laser, Bose-Einstein Condensation, the non-locality of the Einstein-Podolsky-Rosen effect, and quantum teleportation.

Poland. In mid-August 1920—between the 14th and 16th, but what happened on the 15th, the feast of the Assumption of the Blessed Virgin Mary, was decisive—Marshal Iozef Pilsudski launched a counteroffensive that, led by General Iozef Haller, stopped the Red Army before Warsaw, while on the Lower Vistula, General Wladyslaw Sikorski threatened to isolate the Bolsheviks’ marching wing, who beat a retreat.

Nobel Prize in Physics to Niels Bohr

American expedition to the Gobi Desert in Mongolia finds 25 dinosaur eggs and fossils dating back 85 to 25 million years.

Northern Russia: Kholmogory (or Kholmogory), the first Gulag of the Soviet era, is established. It will be inaugurated in 1924. Sailors from Kronstadt will be imprisoned there after an attempted riot. Once the uprising is quelled, the insurgents are lined up on the pier. “Count yourself!” The odd numbers step forward and are shot on the spot. The even numbers will receive 10 years in the Gulag in Kholmogory. After several escape attempts, a military unit is sent in. The camp director commits suicide. And the surviving sailors are transferred to the special-regime camp on the Solovki Islands.

American logician Emil Post invents the formal system that will become known as “Post’s System.”

Ramanujan died in Madras, India, where he had moved for a period of convalescence on the advice of Hardy.

First double non-stop Atlantic crossing: British airship R34

Bela Kun’s revolutionary communist regime in Hungary

Hungary. When Bela Kun takes power, young John von Neumann is transferred to Vienna and then to the Adriatic. He will develop a lifelong aversion to communism.

Versailles. Germany is condemned to pay, within thirty years, in goods or money, the sum of 132 billion gold marks. According to Keynes, a sum exceeding 2 billion would be unreasonable and inconvenient for the international community.

John Maynard Keynes raises the alarm, arguing that the reparations imposed on Germany will cause problems for the world economy.

Poland. The Polish Constituent Assembly appointed Iozef Pilsudski, a former Austro-Hungarian officer who fought on the Russian front, as head of the Republic. A month later, Pilsudski launched an army toward Kiev, Ukraine, composed of Poles and Ukrainian rebels commanded by Simon Vasilyovich Petliura, leader of the proclaimed Ukrainian People’s Republic (White). The Red Army, still engaged on too many fronts in 1919, limited itself to defending the vital regions of European Russia and Moscow. But the following year, the Soviets struck back. The Poles and their Ukrainian allies were pushed back to the gates of Lviv and Warsaw, while on the Lower Vistula, Soviet cavalry corps, led by Ghaia Dmitriyevic Ghai Khan, pressed toward Torun. Meanwhile, in southern Ukraine, command of the anti-Bolshevik southern armies was assumed by General Pyotr Nikolaevich Wrangel, who had replaced Denikin after the defeat at Orel in 1919 and was now reduced to defending little more than Crimea. Having reorganized his remaining troops (spring 1920), he launched a final, desperate offensive, which led him to defeat the Reds, pursuing them to the Dnepr (river: October 1920).