Gustave Le Bon
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Charles-Marie Gustave Le Bon was a leading French polymath whose areas of interest included anthropology, psychology, sociology, medicine, invention, and physics. He is best known for his 1895 work The Crowd: A Study of the Popular Mind, which is considered one of the seminal works of crowd psychology.
Portrait of Gustave Le Bon, c. 1870
Gustave Le Bon on horseback, c. 1895
Gustave Le Bon, c. 1900
Mass–energy equivalence
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In physics, mass–energy equivalence is the relationship between mass and energy in a system's rest frame, where the two quantities differ only by a multiplicative constant and the units of measurement. The principle is described by the physicist Albert Einstein's formula: . In a reference frame where the system is moving, its relativistic energy and relativistic mass obey the same formula.
Task Force One, the world's first nuclear-powered task force. Enterprise, Long Beach and Bainbridge in formation in the Mediterranean, 18 June 1964. Enterprise crew members are spelling out Einstein's mass–energy equivalence formula E = mc2 on the flight deck.
In the revised English edition of Isaac Newton's Opticks, published in 1717, Newton speculated on the equivalence of mass and light.
Photo of Albert Einstein in 1921