Physics In History

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Leonard Susskind on Einstein and Quantum mechanics ✍️ Albert Einstein, who was in many ways the father of quantum mechanics, had a notorious love-hate relation with the subject. His debates with Niels Bohr—Bohr completely accepting of quantum mechanics and Einstein deeply skeptical— are famous in the history of science. It was generally accepted by most physicists that Bohr won and Einstein lost. My own feeling, I think shared by a growing number of physicists, is that this attitude does not do justice to Einstein’s views. Both Bohr and Einstein were subtle men. Einstein tried very hard to show that quantum mechanics was inconsistent; Bohr, however, was always able to counter his arguments. But in his final attack Einstein pointed to something so deep, so counterintuitive, so troubling, and yet so exciting, that at the beginning of the twenty-first century it has returned to fascinate theoretical physicists. Bohr’s only answer to Einstein’s last great discovery—the discovery of entanglement—was to ignore it.

What do you think? ✍️

Sir Isaac Newton ✍️

Leonardo da Vinci wrote the vast majority of his private notes right-to-left (mirror script), almost certainly because, as a left-hander, this prevented smudging wet ink. His journals burst with backwards Italian, diagrams, and inventions.

✍️

What do you think? ✍️

Some black holes might have formed immediately after the Big Bang (primordial black holes) rather than through stellar collapse, and could theoretically account for dark matter, though this remains speculative.

The individual is ephemeral, races and nations come and pass away, but man remains. - Nikola Tesla

Maria Skłodowska-Curie's handwritten notes on radioactivity. Courtesy of Wellcome images.

Niels Bohr and Werner Heisenberg together on a skiing vacation in Tyrol, 1932. As always, Bohr is taking notes.

Mathematician Srinivasa Ramanujan’s personal handwritten mathematical notes and letters.

Details on Schrödinger equation. ✍️

In 1704, Sir Isaac Newton predicted that the world would end in 2060.

Schrödinger equation ✍️ iℏ∂ψ/∂t = (-ℏ²/2m)∇²ψ + Vψ

" If you want to Learn something, teach it !"

Formation of conic sections ✍️ Circle: When the cutting plane is perpendicular to the axis of the cone, the cross-section is a circle. Ellipse: When the plane is angled, but still cuts through only one cone (without being parallel to the side of the cone), the result is an ellipse. Parabola: If the plane is parallel to the side (slant) of the cone, it creates a parabola. Hyperbola: If the plane cuts both halves of the double cone, it forms a hyperbola - two separate curves.

Did time have a beginning, or is asking "before the Big Bang" meaningless? ✍️

The Golden Ratio (φ ≈ 1.618) has a rare self-referential identity: φ² = φ + 1. It's also the limiting ratio of consecutive Fibonacci numbers - divide any Fibonacci number by its predecessor (13/8, 21/13, 34/21....) and the result converges toward φ, though it never exactly reaches it. No other positive real number satisfies both properties simultaneously.

Kepler's laws of planetary motion, formulated by Johannes Kepler in the early 17th century, revolutionized our understanding of how planets orbit the Sun. 1. Law of Ellipses (First Law): Each planet orbits the Sun in a path called an ellipse, with the Sun at one of the two foci of the ellipse. This law contradicted the long-held belief that planets moved in perfect circles. An ellipse is a closed curve that is oval in shape, and the degree to which it is stretched out can vary. 2. Law of Equal Areas (Second Law): A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This means that when a planet is closer to the Sun (at perihelion), it travels faster than when it is farther from the Sun (at aphelion). This law describes the conservation of angular momentum, where the speed of the planet increases as it nears the Sun and decreases as it moves away. 3. Law of Harmonies (Third Law): The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. In simpler terms, this law relates the time a planet takes to orbit the Sun (its orbital period) to the average distance from the Sun. Kepler's laws were derived from meticulous observations made by Tycho Brahe, and they laid the groundwork for Isaac Newton's theory of universal gravitation. They are fundamental to our understanding of solar system dynamics and are still used today to describe the motion of planets and other celestial bodies.