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Several months after Einstein presented his papers on General theory of relativity in 1915, a young German soldier serving at the Russian front solved Einstein's field equations. His solutions revealed the existence of black holes.

Einstein's "biggest blunder": 📰 In 1917, Albert Einstein introduced the cosmological constant into his theory of general relativity in order to maintain a static universe, as it was widely believed at the time. However, just over a decade later, Edwin Hubble's observations of the expanding universe rendered the cosmological constant unnecessary. Einstein later referred to this as his "biggest blunder," although recent discoveries suggest that the constant might play a role in explaining dark energy.

Edwin Hubble was an American astronomer who discovered that galaxies exist beyond the Milky Way and that the universe is expanding, leading to the formulation of Hubble's Law. His work laid the foundation for the Big Bang theory and revolutionized our understanding of the cosmos. Also The Hubble Space Telescope is named in his honor.

Lemaître is credited with the first definitive formulation of the idea of an expanding universe and what was to become known as the Big Bang theory of the origin of the universe, which Lemaître himself called his “hypothesis of the primeval atom” or the “Cosmic Egg”.

"This circumstance of an expanding universe is irritating." Einstein did not like the idea that the universe had a beginning or that it was constantly changing in size. He preferred a static and eternal universe that was balanced by a cosmological constant, a term he added to his own equations of general relativity. However, many scientists who studied his equations found solutions that suggested otherwise. One of them was George Lemaitre, a Belgian priest and physicist, who proposed in 1927 that the universe began with a “primeval atom” that exploded and gave rise to the expanding universe. He also predicted that the expansion rate of the universe should be proportional to its distance from the center of the explosion, a relation now known as Hubble’s law. Another scientist who challenged Einstein’s view was Edwin Hubble, an American astronomer, who observed in 1929 that the galaxies were receding from each other at a speed that increased with their distance, confirming Lemaitre’s prediction. He also showed that the universe was not static, but dynamic and evolving. Einstein was initially reluctant to accept these findings, but he eventually changed his mind and admitted that his cosmological constant was a mistake. He said that Lemaitre’s theory was "the most beautiful and satisfactory explanation of creation to which I have ever listened". He also praised Hubble’s work and said that it was "one of the greatest discoveries in science". Initial quote was A. Einstein's remarks on the Big Bang and the expanding universe as mentioned in a letter to Willem de Sitter. Source: HAVE ASTRONOMERS by Robert Jastrow, 1978.

Gabriel's Horn, also known as Torricelli's Trumpet, is a geometric figure that has the paradoxical property of having infinite surface area but finite volume. It is formed by revolving the curve y = ¹⁄ₓ around the x-axis from x = 1 to infinity. ✍️

General Relativity for babies ✍️

One of the earliest examples of a systematic approach to empirical inquiry is found in the Edwin Smith papyrus, an ancient Egyptian medical textbook from c. 1600 BCE, which describes the examination, diagnosis, treatment, and prognosis of various diseases.

Finally we shall place the Sun himself at the center of the Universe. All this is suggested by the systematic procession of events and the harmony of the whole Universe, if only we face the facts, as they say, "with both eyes open." - Nicolaus Copernicus

Isaac Asimov on 'the usage of science and technology' Science is a systematic method for studying and working out those generalizations that seem to describe the behavior of the universe. It could exist as a purely intellectual game that would never affect the practical life of human beings either for good or evil, and that was very nearly the case in ancient Greece, for instance. Technology is the application of scientific findings to the tools of everyday life, and that application can be wise or unwise, useful or harmful. Very often, those who govern technological decisions are not scientists and know little about science. [Image courtesy: the Library Of Congress]

Richard Feynman with Neil Armstrong at the Rogers Commission Report Press Conference, June 1986.

Why does a scientist study nature? by Henri Poincaré 💭 The scientist does not study nature because it is useful to do so. He studies it because he takes pleasure in it, and he takes pleasure in it because it is beautiful. If nature were not beautiful it would not be worth knowing, and life would not be worth living. I am not speaking, of course, of the beauty which strikes the senses, of the beauty of qualities and appearances. I am far from despising this, but it has nothing to do with science. What I mean is that more intimate beauty which comes from the harmonious order of its parts, and which a pure intelligence can grasp. -- as mentioned in The Selection of Facts, p. 22, Ch. 1 [Image courtesy: Hulton-Deutsch Collection/Corbis]

"Any fool can know. The point is to understand." -- A. Einstein (1879 - 1955)

All my life, I've wondered about life beyond the earth. On those countless other planets that we think circle other suns, is there also life? Might the beings of other worlds resemble us, or would they be astonishingly different? What would they be made of? In the vast Milky Way galaxy, how common is what we call life? The nature of life on earth and the quest for life elsewhere are the two sides of the same question: the search for who we are. - Dr. Carl Sagan

Richard Feynman on quantum mechanical nature of nature ✍️ Nature isn't classical, dammit, and if you want to make a simulation of nature, you'd better make it quantum mechanical, and by golly it's a wonderful problem, because it doesn't look so easy. -- as mentioned in International Journal of Theoretical Physics, vol. 21, 1982

Sir James Chadwick (20 October 1891 – 24 July 1974) was an esteemed physicist renowned for his discovery of the neutron in 1932, for which he was awarded the Nobel Prize in Physics in 1935. His pivotal contributions to nuclear physics and leadership in the British team of the Manhattan Project greatly influenced the development of atomic energy.

Two titans of Quantum Field Theory: Richard Feynman and Chen Ning Yang c. 1950s. Both Nobel Laureates. Yang's best known for his role as co-discoverer of parity violation while Feynman had significant contributions to the development of the QED.

In the mid-20th century, the invention and development of bubble chambers revolutionized particle physics experiments. Bubble chambers allowed scientists to observe the tracks of subatomic particles by creating a superheated liquid that formed bubbles along the particle's path, making it visible for analysis.

The smallest positive integer that is divisible by all the numbers from 1 to 20 is 232,792,560. This is also known as the least common multiple of the first 20 natural numbers.