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From Wikipedia, the free encyclopedia

The native form of this personal name is Szilárd Leó. This article uses the Western name order.
Leó Szilárd

Leó Szilárd (1898–1964) when he was 18 years old
Born February 11, 1898(1898-02-11)
Budapest, Austria-Hungary
Died May 30, 1964 (aged 66)
La Jolla, California, U.S.
Residence Hungary
United States
Nationality Hungarian
Ethnicity Jewish-Hungarian
Fields Physicist
Institutions Technical University of Berlin
Humboldt University of Berlin
Columbia University
University of Chicago
Brandeis University
Salk Institute
Alma mater Technische Universität Berlin
Humboldt Universität zu Berlin
Doctoral advisor Max von Laue
Other academic advisors Albert Einstein
Notable students Bernard T. Feld
Known for Nuclear chain reaction
Szilárd petition
Einstein–Szilárd letter
Cobalt bomb
Absorption refrigerator
Szilárd Engine
Influenced James L. Tuck
Notable awards Atoms for Peace Award (1959)

Leó Szilárd (Hungarian: Szilárd Leó, February 11, 1898 – May 30, 1964) was a Hungarian physicist who conceived the nuclear chain reaction and worked on the Manhattan Project. He was born in Budapest in the Austro-Hungarian Empire, and died in La Jolla, California.


Early life

Szilárd was born into a Jewish family of Budapest at the time of the Austro-Hungarian monarchy before World War I as the son of a civil engineer. From 1908–1916 he attended Reáliskola in his home town. He was enrolled as an engineering student at Budapest Technical University during 1916 but had to join the Austro-Hungarian Army during 1917 as officer-candidate where he was discharged honorably at the end of the war. During 1919 he resumed engineering studies at Budapest Technical University but soon decided to leave Hungary because of the rising antisemitism under the Horthy regime which caused the introduction of a numerus clausus for Jewish students at Hungary's universities. He continued engineering studies at Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg. He soon changed to physics there and took physics classes from Einstein, Planck, and Max von Laue. His dissertation on thermodynamics Über die thermodynamischen Schwankungserscheinungen (On The Manifestation of Thermodynamic Fluctuations) during 1922 was praised by Einstein and awarded the highest honor. During 1923 he received the doctorate in physics from the Humboldt University of Berlin. He was appointed as assistant to von Laue at the University of Berlin's Institute for Theoretical Physics during 1924. During 1927 he finished his habilitation and became a Privatdozent (instructor) in Physics at University of Berlin. During his time in Berlin he was working on numerous technical inventions (1928 German patent application on the linear accelerator, 1929 German patent application on the cyclotron, since 1926 work with Einstein on the construction of a refrigerator without moving parts (US patent 1,781,541 on November 11, 1930).

Developing the idea of the nuclear chain reaction

An image from the Fermi–Szilárd "neutronic reactor" patent

During 1933 Szilárd fled to London to escape Nazi persecution, where he read an article in The Times summarizing a speech given by Ernest Rutherford which rejected the possibility of using atomic energy for practical purposes:

We might in these processes obtain very much more energy than the proton supplied, but on the average we could not expect to obtain energy in this way. It was a very poor and inefficient way of producing energy, and anyone who looked for a source of power in the transformation of the atoms was talking moonshine. But the subject was scientifically interesting because it gave insight into the atoms[1]

Although nuclear fission had not yet been discovered, Szilárd was reportedly so annoyed at this dismissal that he conceived of the idea of the nuclear chain reaction while walking to work at St Bartholomew's Hospital waiting for traffic lights to change on Southampton Row in Bloomsbury, though his friend Jacob Bronowski notes that he never knew Szilárd to wait for traffic lights.[2] The following year he filed for a patent on the concept.

Szilárd first attempted to create a chain reaction using beryllium and indium, but these elements did not produce a chain reaction. During 1936, he assigned the chain-reaction patent to the British Admiralty to ensure its secrecy (GB patent 630726). Szilárd also was the co-holder, with Nobel Laureate Enrico Fermi, of the patent on the nuclear reactor (U.S. Patent 2,708,656).

During 1938 Szilárd accepted an offer to conduct research at Columbia University in Manhattan, and moved to New York, and was soon joined by Fermi. After learning about the successful nuclear fission experiment conducted during 1939 in Germany by Otto Hahn, Fritz Strassmann, Lise Meitner, and Otto Robert Frisch, Szilárd and Fermi concluded that uranium would be the element capable of sustaining a chain reaction. Szilárd and Fermi conducted a simple experiment at Columbia and discovered significant neutron multiplication in uranium, proving that the chain reaction was possible and enabling nuclear weapons. Szilárd later described the event: "We turned the switch and saw the flashes. We watched them for a little while and then we switched everything off and went home." He understood the implications and consequences of this discovery, though. "That night, there was very little doubt in my mind that the world was headed for grief."[3]

At around that time the Germans and others were in a race to produce a nuclear chain reaction. German attempts to control the chain reaction sought to do so using graphite, but these attempts proved unsuccessful. Szilárd realized graphite was indeed perfect for controlling chain reactions, just as the Germans had determined, but that the method of producing graphite used boron carbide rods, and the minute amount of boron impurities in the manufactured graphite was enough to stop the chain reaction. Szilárd had graphite manufacturers produce boron-free graphite. As a result, the first human-controlled chain reaction occurred on 2 December 1942.[4]

The Manhattan Project

Szilárd was directly responsible for the creation of the Manhattan Project. He drafted a confidential letter to Franklin D. Roosevelt explaining the possibility of nuclear weapons, warning of Nazi work on such weapons and encouraging the development of a program which could result in their creation. During August 1939 he approached his old friend and collaborator Albert Einstein and convinced him to sign the letter, lending his fame to the proposal.[5] The Einstein–Szilárd letter resulted in the establishment of research into nuclear fission by the U.S. government and ultimately to the creation of the Manhattan Project; FDR gave the letter to an aide, General Edwin M. "Pa" Watson with the instruction: "Pa, this requires action!"[6] Later, Szilárd relocated to the University of Chicago to continue work on the project. There, along with Fermi, he helped to construct the first "neutronic reactor", a uranium and graphite "atomic pile" in which the first self-sustaining nuclear chain reaction was achieved, during 1942.

As the war continued, Szilárd became increasingly dismayed that scientists were losing control over their research to the military, and argued many times with General Leslie Groves, military director of the project. His resentment towards the U.S. government was exacerbated by his failed attempts to avoid the use of the atomic bomb in war through having a test organized that could be witnessed by Japanese observers who would then have the opportunity to surrender and spare lives.[7]

Szilárd became a naturalized citizen of the United States during 1943.

Views on the use of nuclear weapons

During 1932, Szilárd had read about the fictional "atomic bombs" described in H. G. Wells's science fiction novel The World Set Free. This inspired him to be the first scientist to examine seriously the science of the creation of nuclear weapons. As a scientist, he was the first person to conceive of a device that, using a nuclear chain reaction as fuel, could be used as a bomb.

As a survivor of a devastated Hungary after World War I, and having witnessed the subsequent terror of the Reds and the Whites, Szilárd developed an enduring passion for the preservation of human life and freedom, especially freedom to communicate ideas.

He hoped that the U.S. government would not use nuclear weapons because of their potential for use against civilian populations. Szilárd hoped that the mere threat of such weapons would force Germany and/or Japan to surrender. He drafted the Szilárd petition advocating demonstration of the atomic bomb. However with the European war concluded and the U.S. suffering many casualties in the Pacific Ocean region, the new U.S. President Harry Truman agreed with advisors and chose to use atomic bombs against Hiroshima and Nagasaki over the protestations of Szilárd and other scientists.

After the war

During 1947, Szilárd switched topics of study because of his horror of atomic weapons, changing from physics to molecular biology, working extensively with Aaron Novick. He, Szilárd, proposed, during February 1950, a new kind of nuclear weapon using cobalt as a tamper, a cobalt bomb, which he said might destroy all life on the planet. U.S. News & World Report featured an interview with Szilárd in its August 15, 1960 issue, "President Truman Didn't Understand." He argued that "violence would not have been necessary if we had been willing to negotiate."

During 1961 Szilárd published a book of short stories, The Voice of the Dolphins, in which he dealt with the moral and ethical issues raised by the Cold War and his own role in the development of atomic weapons. The title story described an international biology research laboratory in Central Europe. This became reality after a meeting in 1962 with Victor F. Weisskopf, James Watson and John Kendrew. When the European Molecular Biology Laboratory was established, the library was named The Szilard Library and the library stamp features dolphins.

Szilárd married Gertrud Weiss in 1951.[8]

During 1960, Szilárd was diagnosed with bladder cancer. He underwent radiation therapy at New York's Memorial Hospital using a treatment regimen that he designed himself. A second round of treatment followed during 1962; Szilárd's cancer remained in remission thereafter.

During 1962, Szilárd was part of a group of scientists who founded the Council for a Livable World. The Council's goal was to warn the public and Congress of the threat of nuclear war and encourage rational arms control and nuclear disarmament.

He spent his last years as a fellow of the Salk Institute in San Diego.

During May 1964, Szilárd died in his sleep of a heart attack at the age of sixty-six. At his memorial it was said that Death was required to come to him while he was asleep, or otherwise he would have outwitted it.


  • The crater Szilárd (34.0°N, 105.7°E, 122 km dia.) on the far side of the Moon is named after him.
  • In John Scalzi's science fiction novel The Ghost Brigades, set centuries in the future, the commanding officer of the Colonial Defense Forces is named General Szilard, in honor of the twentieth-century scientist.


He is dramatized in Race for the bomb, a TV production narrating the development of the atomic bomb.

See also


  1. ^ The Times archives, September 12, 1933, "The British association—breaking down the atom"
  2. ^ "Knowledge or Certainty". Jacob Bronowski (writer, presenter). The Ascent of Man. 39:01 minutes in.
  3. ^ Rhodes, "The Making Of The Atomic Bomb", Simon & Schuster, 1986, pg. 292-293
  4. ^ Bethe, Hans A. (2000-03-27). "The German Uranium Project". Physics Today Online 53: 34. doi:10.1063/1.1292473.  
  5. ^ The Atomic Heritage Foundation. "Einstein's Letter to Franklin D. Roosevelt". Retrieved 2007-05-26.  
  6. ^ The Atomic Heritage Foundation. ""Pa, this requires action!"". Retrieved 2007-05-26.  
  7. ^ "Knowledge or Certainty". Jacob Bronowski (writer, presenter). The Ascent of Man. 41:14 minutes in.
  8. ^ Esterer, Arnulf K.; Luise A. Esterer (1972). Prophet of the Atomic Age: Leo Szilard. Julian Messner. pp. 148. ISBN 067132523X.  


  • Szilard, Leo (1992). The Voice of the Dolphins: And Other Stories (Expanded edition from 1961 original ed.). Stanford, CA.: Stanford University Press. ISBN 0804717540.  
  • Szilard, Leo; Gertrud Weiss-Szilard (1978). Leo Szilard: His Version of the Facts : Selected Recollections and Correspondence. Spencer R. Weart (ed.). Cambridge, MA.: The MIT Press. ISBN 0262690705.  
  • Lanouette, William; Bela Silard (1992). Genius in the Shadows: A Biography of Leo Szilárd: The Man Behind The Bomb. New York: Charles Scribner's Sons. ISBN 0684190117.  
  • Esterer, Arnulf K.; Luise A. Esterer (1972). Prophet of the Atomic Age: Leo Szilard. New York: Julian Messner. ISBN 067132523X.  

External links





Up to date as of January 14, 2010
(Redirected to Leó Szilárd article)

From Wikiquote

Even in times of war, you can see current events in their historical perspective, provided that your passion for the truth prevails over your bias in favor of your own nation.

Leó Szilárd (1898-02-111964-05-30) was a Hungarian-American physicist, and probably the first scientist to take seriously the idea of developing real atomic bombs; he drafted the famous letter sent by Albert Einstein to U.S. President Franklin Delano Roosevelt that was largely responsible for initiating the Manhattan Project.



  • Suppose Germany had developed two bombs before we had any bombs. And suppose Germany had dropped one bomb, say, on Rochester and the other on Buffalo, and then having run out of bombs she would have lost the war. Can anyone doubt that we would then have defined the dropping of atomic bombs on cities as a war crime, and that we would have sentenced the Germans who were guilty of this crime to death at Nuremberg and hanged them?
    But, again, don't misunderstand me. The only conclusion we can draw is that governments acting in a crisis are guided by questions of expediency, and moral considerations are given very little weight, and that America is no different from any other nation in this respect.
    • "President Truman Did Not Understand" in U.S. News & World Report (1960-08-15); Unsourced variant: If the Germans had dropped atomic bombs on cities instead of us, we would have defined the dropping of atomic bombs on cities as a war crime, and we would have sentenced the Germans who were guilty of this crime to death at Nuremberg and hanged them.
  • A great power imposes the obligation of exercising restraint, and we did not live up to this obligation. I think this affected many of the scientists in a subtle sense, and it diminished their desire to continue to work on the bomb.
    • "President Truman Did Not Understand" in U.S. News & World Report (1960-08-15)
That night I knew the world was headed for sorrow...
  • Even if we accept, as the basic tenet of true democracy, that one moron is equal to one genius, is it necessary to go a further step and hold that two morons are better than one genius?
    • The Voice of the Dolphins: And Other Stories (1961)
  • We turned the switch, we saw the flashes, we watched them for about ten minutes — and then we switched everything off and went home. That night I knew the world was headed for sorrow...
    • On the experiment at University of Chicago which indicated a nuclear chain reaction was possible, as quoted in the Boston University Graduate Journal (1968)
    • Variant: We turned the switch, saw the flashes, watched for ten minutes, then switched everything off and went home. That night I knew the world was headed for sorrow.

Are We on the Road to War?

Speech at Harvard Law School (1961-11-17) ; republished in Toward a Livable World: Leo Szilard and the Crusade for Nuclear Arms Control (1987) by Leo Szilard, Helen S. Hawkins, G. Allen Greb, and Gertrud Weiss Szilard, p. 432
  • I sometimes have the feeling that I have lived through all this before and, in a sense, I have. I was sixteen years old when the first World War broke out, and I lived at that time in Hungary. From reading the newspapers in Hungary, it would have appeared that, whatever Austria and Germany did was right and whatever England, France, Russia, or America did was wrong. A good case could be made out for this general thesis, in almost every single instance. It would have been difficult for me to prove, in any single instance, that the newspapers were wrong, but somehow, it seemed to me unlikely that the two nations located in the center of Europe should be invariably right, and that all the other nations should be invariably wrong. History, I reasoned, would hardly operate in such a peculiar fashion, and it didn't take long until I began to hold views which were diametrically opposed to those held by the majority of my schoolmates.
  • Even in times of war, you can see current events in their historical perspective, provided that your passion for the truth prevails over your bias in favor of your own nation.
  • The people who have sufficient passion for the truth to give the truth a chance to prevail, if it runs counter to their bias, are in a minority. How important is this "minority?" It is difficult to say at this point, for, at the present time their influence on governmental decisions is not perceptible.


  • A scientist's aim in a discussion with his colleagues is not to persuade, but to clarify.
  • Don't lie if you don't have to.
  • I'm all in favor of the democratic principle that one idiot is as good as one genius, but I draw the line when someone takes the next step and concludes that two idiots are better than one genius.
  • If you want to succeed in the world, you don't have to be much cleverer than other people. You just have to be one day earlier.
  • If one knows only what one is told, one does not know enough to be able to arrive at a well-balanced decision.

Quotes about Szilárd

  • I had not been long back from Hiroshima when I heard someone say, in Szilárd's presence; that it was the tragedy of scientists that their discoveries were used for destruction. Szilárd replied, as he more than anyone else had the right to reply; that it was not the tragedy of scientists, it is the tragedy of mankind.

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