When did Einstein Publish E=mc²?
Einstein first published the equation E=mc² (energy is equal to mass multiplied by the speed of light squared) in 1905 in the journal Annalen der Physik. He went on to fully generalise the equivalence of mass and energy in 1907.
The paper was received on 27 September 1905 and was a three-page supplement to his first paper on special relativity completed in June of the same year. The paper is titled: "Does the Inertia of a Body Depend on its Energy Content?" In this article the equation appears with different letters used to represent energy, mass and the speed of light
The equation shows that mass and energy are related and that one can be transformed into the other. But because the speed of light is such a huge number, roughly 300,000,000 meters per second, it means that even a small amount of mass can potentially be converted into a huge amount of energy.
Who was Leo Szilard?
Leo Szilard was a Hungarian theoretical physicist, born in Budapest on 11 February 1898. "His deepest ambition," wrote the historian Richard Rhodes "more profound even than his commitment to science, was somehow to save the world."
One of Szilard's sidelines and passions was invention. In 1927, while they were both in Berlin, Szilard and Einstein filed their first of eight joint patents for an electromagnetic pump designed for home refrigerators. The design proved too noisy for domestic use, but would later become the basis of the cooling system used in the 'breeder' nuclear reactors of the 1950s and 1960s.
On 12 September 1933, Szilard was 35 years old, had fled Nazi Germany earlier that year and was living in a London hotel. Crossing Southampton Row while out walking that day, he conceived the idea of a nuclear chain reaction.
Szilard worked on the Manhattan project at the Metallurgical Laboratory or Met Lab at the University of Chicago where he was chief physicist and worked mainly on reactor design. After World War Two, he was an active participant in the Pugwash Conferences on Science and World Affairs which drew their inspiration from the Russell-Einstein Manifesto of 1955, and founded the first political action committee for arms control, the Council for a Livable World.
When, where and how was nuclear fission first discovered?
The fission of uranium was first discovered by an experiment conducted by the nuclear chemists Otto Hahn and Fritz Strassmann, working at the Kaiser Wilhelm Institute in Berlin. Just before Christmas 1938 they bombarded a solution of uranium nitrate with neutrons. Expecting to find new heavier elements they were surprised when their analysis revealed the presence of barium, an element roughly half the mass of uranium.
Conferring with their colleague, the physicist Lise Meitner, they realised that they have in fact split the uranium nucleus into two roughly equal parts. Meitner, an Austrian Jew living in exile in Sweden, and her cousin Otto Frisch were the first to work out what had happened. Meitner used E=mc² to calculate the vast energy released in the reaction which she and her cousin called nuclear fission. Frisch and Meitner published their interpretation of Hahn and Strassmann's experiment in Nature in 1939.
How influential was Einstein's letter to Roosevelt?
Einstein's letter was delivered to the President by Alexander Sachs on 11 October 1939. Following the meeting Dr Lyman Briggs, director of the Bureau of Standards, was ordered to set up a committee to investigate. The first meeting of the Advisory Committee on Uranium was held at the Carleton Hotel, Washington on 21 October. At the meeting, the committee awarded Szilard and Fermi $6,000 to purchase the graphite they needed to continue their work on the chain reaction and the development of the first nuclear reactor.
In 1941 the report of the MAUD committee, the British equivalent of Briggs' committee in the US, reached the President Roosevelt. The report concluded that the "scheme for a uranium bomb is practicable and likely to lead to decisive results in the war". Central to that conclusion was research from early 1940 by Otto Frisch and Rudolf Pieirls that concluded that the critical mass required to achieve a chain reaction was much smaller than had previously been thought.
In November, President Roosevelt authorised a dedicated nuclear programme - which would become known as the Manhattan Project after it was taken over by the army in June of 1942.
While Einstein's letter did not lead directly to the Manhattan project, it did result in funding that allowed scientists to continue research into the chain reaction before the start of the full scale project. Without this head start, the atomic bomb would not have been ready before the end of World War Two.
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