Werner Heisenberg

Werner Heisenberg (5 December 1901 – 1 February 1976) was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory. In addition, he made important contributions to nuclear physics, quantum field theory, and particle physics.

Heisenberg, along with Max Born and Pascual Jordan, set forth the matrix formulation of quantum mechanics in 1925. Heisenberg was awarded the 1932 Nobel Prize in Physics for the creation of quantum mechanics, and its application especially to the discovery of the allotropic forms of hydrogen.

Following World War II, he was appointed director of the Kaiser Wilhelm Institute for Physics, which was soon thereafter renamed the Max Planck Institute for Physics. He was director of the institute until it was moved to Munich in 1958, when it was expanded and renamed the Max Planck Institute for Physics and Astrophysics.

From 1924 to 1927, Heisenberg was a Privatdozent at Göttingen. From 17 September 1924 to 1 May 1925, under an International Education BoardRockefeller Foundation fellowship, Heisenberg went to do research with Niels Bohr, director of the Institute of Theoretical Physics at the University of Copenhagen. He returned to Göttingen and with Max Born and Pascual Jordan, over a period of about six months, developed the matrix mechanicsformulation of quantum mechanics. On 1 May 1926, Heisenberg began his appointment as a university lecturer and assistant to Bohr in Copenhagen. It was in Copenhagen, in 1927, that Heisenberg developed his uncertainty principle, while working on the mathematical foundations of quantum mechanics. On 23 February, Heisenberg wrote a letter to fellow physicist Wolfgang Pauli, in which he first described his new principle. In his paper on the uncertainty principle, Heisenberg used the word "Ungenauigkeit" (imprecision).

Heisenberg was also president of the German Research Council, chairman of the Commission for Atomic Physics, chairman of the Nuclear Physics Working Group, and president of the Alexander von Humboldt Foundation.

In 1927, Heisenberg was appointed ordentlicher Professor (ordinarius professor) of theoretical physics and head of the department of physics at the Universität Leipzig; he gave his inaugural lecture on 1 February 1928. In his first paper published from Leipzig, Heisenberg used the Pauli exclusion principle to solve the mystery of ferromagnetism.

In Heisenberg's tenure at Leipzig, the quality of doctoral students, post-graduate and research associates who studied and worked with Heisenberg there is attested to by the acclaim later earned by these people; at various times, they included: Erich Bagge, Felix Bloch, Ugo Fano, Siegfried Flügge, William Vermillion Houston, Friedrich Hund, Robert S. Mulliken, Rudolf Peierls, George Placzek,Isidor Isaac Rabi, Fritz Sauter, John C. Slater, Edward Teller, John Hasbrouck van Vleck, Victor Frederick Weisskopf, Carl Friedrich von Weizsäcker, Gregor Wentzel and Clarence Zener.

In early 1929, Heisenberg and Pauli submitted the first of two papers laying the foundation for relativistic quantum field theory. Also in 1929, Heisenberg went on a lecture tour in the United States, Japan, China, and India.

Shortly after the discovery of the neutron by James Chadwick in 1932, Heisenberg submitted the first of three papers on his neutron-proton model of the nucleus. He was awarded the 1932Nobel Prize in Physics.

In 1928, the British mathematical physicist P. A. M. Dirac had derived the relativistic wave equation of quantum mechanics, which implied the existence of positive electrons, later to be namedpositrons. In 1932, from a cloud chamber photograph of cosmic rays, the American physicist Carl David Anderson identified a track as having been made by a positron. In mid-1933, Heisenberg presented his theory of the positron. His thinking on Dirac's theory and further development of the theory were set forth in two papers. The first, Bemerkungen zur Diracschen Theorie des Positrons (Remarks on Dirac's theory of the positron) was published in 1934, and the second, Folgerungen aus der Diracschen Theorie des Positrons (Consequences of Dirac's Theory of the Positron), was published in 1936. In these papers Heisenberg was the first to reinterpret the Dirac equation as a "classical" field equation for any point particle of spin ħ/2, itself subject to quantization conditions involving anti-commutators. Thus reinterpreting it as a (quantum) field equation accurately describing electrons, Heisenberg put matter on the same footing as electromagnetism: as being described by relativistic quantum field equations which allowed the possibility of particle creation and destruction.

In the early 1930s in Germany, the deutsche Physik movement was anti-Semitic and anti-theoretical physics, especially including quantum mechanics and the theory of relativity. As applied in the university environment, political factors took priority over the historically applied concept of scholarly ability, even though its two most prominent supporters were the Nobel Laureates in PhysicsPhilipp Lenard and Johannes Stark.

After Adolf Hitler came to power in 1933, Heisenberg was attacked in the press as a "White Jew" by elements of the deutsche Physik (German Physics) movement for his insistence on teaching about the roles of Jewish scientists. As a result, he came under investigation by the SS. This was over an attempt to appoint Heisenberg as successor to Arnold Sommerfeld at the University of Munich. The issue was resolved in 1938 by Heinrich Himmler, head of the SS. While Heisenberg was not chosen as Sommerfeld's successor, he was rehabilitated to the physics community during theThird Reich. Nevertheless, supporters of deutsche Physik launched vicious attacks against leading theoretical physicists, including Arnold Sommerfeld and Heisenberg. On 29 June 1936, a National Socialist Party newspaper published a column attacking Heisenberg. On 15 July 1937, he was attacked in a journal of the SS. This was the beginning of what is called the Heisenberg Affair.

In mid-1936, Heisenberg presented his theory of cosmic-ray showers in two papers. Four more papers appeared in the next two years.

Heisenberg’s paper establishing quantum mechanics has puzzled physicists and historians. His methods assume that the reader is familiar with Kramers-Heisenberg transition probability calculations. The main new idea, noncommuting matrices, is justified only by a rejection of unobservable quantities. It introduces the non-commutative multiplication of matrices by physical reasoning, based on the correspondence principle, despite the fact that Heisenberg was not then familiar with the mathematical theory of matrices. The path leading to these results has been reconstructed in MacKinnon, 1977, and the detailed calculations are worked out in Aitchison et al.

In June 1939, Heisenberg bought a summer home for his family in Urfeld, in southern Germany. He also traveled to the United States in June and July, visiting Samuel Abraham Goudsmit, at theUniversity of Michigan in Ann Arbor. However, Heisenberg refused an invitation to emigrate to the United States. He did not see Goudsmit again until six years later, when Goudsmit was the chief scientific advisor to the American Operation Alsos at the close of World War II. Ironically, Heisenberg was arrested under Operation Alsos and detained in England under Operation Epsilon.

In Copenhagen, Heisenberg and H. Kramers collaborated on a paper on dispersion, or the scattering from atoms of radiation whose wavelength is larger than the atoms. They showed that the successful formula Kramers had developed earlier could not be based on Bohr orbits, because the transition frequencies are based on level spacings which are not constant. The frequencies which occur in the Fourier transform of sharp classical orbits, by contrast, are equally spaced. But these results could be explained by a semi-classical Virtual State model: the incoming radiation excites the valence, or outer, electron to a virtual state from which it decays. In a subsequent paper Heisenberg showed that this virtual oscillator model could also explain the polarization of fluorescent radiation.

These two successes, and the continuing failure of the Bohr-Sommerfeld model to explain the outstanding problem of the anomalous Zeeman effect, led Heisenberg to use the virtual oscillator model to try to calculate spectral frequencies. The method proved too difficult to immediately apply to realistic problems, so Heisenberg turned to a simpler example, the anharmonic oscillator.

The dipole oscillator consists of a simple harmonic oscillator, which is thought of as a charged particle on a spring, perturbed by an external force, like an external charge. The motion of the oscillating charge can be expressed as a Fourier series in the frequency of the oscillator. Heisenberg solved for the quantum behavior by two different methods. First, he treated the system with the virtual oscillator method, calculating the transitions between the levels that would be produced by the external source.

He then solved the same problem by treating the anharmonic potential term as a perturbation to the harmonic oscillator and using the perturbation methods that he and Born had developed. Both methods led to the same results for the first and the very complicated second order correction terms. This suggested that behind the very complicated calculations lay a consistent scheme.

So Heisenberg set out to formulate these results without any explicit dependence on the virtual oscillator model. To do this, he replaced the Fourier expansions for the spatial coordinates by matrices, matrices which corresponded to the transition coefficients in the virtual oscillator method. He justified this replacement by an appeal to Bohr’s correspondence principle and the Pauli doctrine that quantum mechanics must be limited to observables.

On 9 July, Heisenberg gave Born this paper to review and submit for publication. When Born read the paper, he recognized the formulation as one which could be transcribed and extended to the systematic language of matrices, which he had learned from his study under Jakob Rosanes at Breslau University. Born, with the help of his assistant and former student Pascual Jordan, began immediately to make the transcription and extension, and they submitted their results for publication; the paper was received for publication just 60 days after Heisenberg's paper. A follow-on paper was submitted for publication before the end of the year by all three authors. (A brief review of Born's role in the development of the matrix mechanics formulation of quantum mechanics along with a discussion of the key formula involving the non-commutivity of the probability amplitudes can be found in an article by Jeremy Bernstein, Max Born and the Quantum Theory. A detailed historical and technical account can be found in Mehra and Rechenberg's book The Historical Development of Quantum Theory. Volume 3. The Formulation of Matrix Mechanics and Its Modifications 1925–1926.)

Up until this time, matrices were seldom used by physicists; they were considered to belong to the realm of pure mathematics. Gustav Mie had used them in a paper on electrodynamics in 1912 and Born had used them in his work on the lattices theory of crystals in 1921. While matrices were used in these cases, the algebra of matrices with their multiplication did not enter the picture as they did in the matrix formulation of quantum mechanics.

Born had learned matrix algebra from Rosanes, as already noted, but Born had also learned Hilbert's theory of integral equations and quadratic forms for an infinite number of variables as was apparent from a citation by Born of Hilbert's work Grundzüge einer allgemeinen Theorie der Linearen Integralgleichungen published in 1912. Jordan, too was well equipped for the task. For a number of years, he had been an assistant to Richard Courant at Göttingen in the preparation of Courant and David Hilbert's book Methoden der mathematischen Physik I, which was published in 1924. This book, fortuitously, contained a great many of the mathematical tools necessary for the continued development of quantum mechanics. In 1926, John von Neumann became assistant to David Hilbert, and he coined the term Hilbert space to describe the algebra and analysis which were used in the development of quantum mechanics.

In 1928, Albert Einstein nominated Heisenberg, Born, and Jordan for the Nobel Prize in Physics, but it was not to be. The announcement of the Nobel Prize in Physics for 1932 was delayed until November 1933. It was at that time that it was announced Heisenberg had won the Prize for 1932 "for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen" and Erwin Schrödinger and Paul Adrien Maurice Dirac shared the 1933 Prize "for the discovery of new productive forms of atomic theory". One can rightly ask why Born was not awarded the Prize in 1932 along with Heisenberg – Bernstein gives some speculations on this matter. One of them is related to Jordan joining the Nazi Party on 1 May 1933 and becoming a Storm Trooper. Hence, Jordan's Party affiliations and Jordan's links to Born may have affected Born's chance at the Prize at that time. Bernstein also notes that when Born won the Prize in 1954, Jordan was still alive, and the Prize was awarded for the statistical interpretation of quantum mechanics, attributable alone to Born.

In 1939, shortly after the discovery of nuclear fission, the German nuclear energy project, also known as the Uranverein (Uranium Club), was begun. Heisenberg was one of the principal scientists leading research and development in the project.^{[citation needed]}

Heisenberg's reaction to Born for Heisenberg receiving the Prize for 1932 and to Born for Born receiving the Prize in 1954 are also instructive in evaluating whether Born should have shared the Prize with Heisenberg. On 25 November 1933, Born received a letter from Heisenberg in which he said he had been delayed in writing due to a "bad conscience" that he alone had received the Prize "for work done in Göttingen in collaboration – you, Jordan and I." Heisenberg went on to say that Born and Jordan's contribution to quantum mechanics cannot be changed by "a wrong decision from the outside." In 1954, Heisenberg wrote an article honoring Max Planck for his insight in 1900. In the article, Heisenberg credited Born and Jordan for the final mathematical formulation of matrix mechanics and Heisenberg went on to stress how great their contributions were to quantum mechanics, which were not "adequately acknowledged in the public eye."

From 15 to 22 September 1941, Heisenberg traveled to German-occupied Copenhagen to lecture and discuss nuclear research and theoretical physics with Niels Bohr. The meeting, and specifically what it might reveal about Heisenberg's intentions concerning developing nuclear weapons for the Nazi regime, is the subject of the award winning Michael Frayn play titled Copenhagen. Documents relating to the Bohr-Heisenberg meeting were released in 2002 by the Niels Bohr Archive and by the Heisenberg family.

On 26 February 1942, Heisenberg presented a lecture to Reich officials on energy acquisition from nuclear fission, after the Army withdrew most of its funding. The Uranium Club was transferred to the Reich Research Council (RFR) in July 1942. On 4 June 1942, Heisenberg was summoned to report to Albert Speer, Germany's Minister of Armaments, on the prospects for converting the Uranium Club's research toward developing nuclear weapons. During the meeting, Heisenberg told Speer that a bomb could not be built before 1945, and would require significant monetary and manpower resources. Five days later, on 9 June 1942, Adolf Hitler issued a decree for the reorganization of the RFR as a separate legal entity under the Reich Ministry for Armament and Ammunition; the decree appointed Reich Marshall Göring as the president.

In September 1942, Heisenberg submitted his first paper of a three-part series on the scattering matrix, or S-matrix, in elementary particle physics. The first two papers were published in 1943^[and the third in 1944. The S-matrix described only observables, i.e., the states of incident particles in a collision process, the states of those emerging from the collision, and stable bound states; there would be no reference to the intervening states. This was the same precedent as he followed in 1925 in what turned out to be the foundation of the matrix formulation of quantum mechanics through only the use of observables.

In February 1943, Heisenberg was appointed to the Chair for Theoretical Physics at the Friedrich-Wilhelms-Universität (today, the Humboldt-Universität zu Berlin). In April, his election to the Preußische Akademie der Wissenschaften (Prussian Academy of Sciences) was approved. That same month, he moved his family to their retreat in Urfeld as Allied bombing increased in Berlin. In the summer, he dispatched the first of his staff at the Kaiser-Wilhelm Institut für Physik to Hechingen and its neighboring town of Haigerloch, on the edge of the Black Forest, for the same reasons. From 18–26 October, he traveled to German-occupied Netherlands. In December 1943, Heisenberg visited German-occupied Poland.

From 24 January to 4 February 1944, Heisenberg traveled to occupied Copenhagen, after the German Army confiscated Bohr's Institute of Theoretical Physics. He made a short return trip in April. In December, Heisenberg lectured in neutral Switzerland.

In January 1945, Heisenberg vacated the Kaiser-Wilhelm Institut für Physik with about all of his staff for the facilities in the Black Forest.

Niels Bohr

Niels Henrik David Bohr ( 7 October 1885 – 18 November 1962) was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was part of a team of physicists working on the Manhattan Project. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Bohr, grew up to be an important physicist who in 1975 also received the Nobel Prize. Bohr has been described as one of the most influential scientists of the 20th century.In 1922, Bohr was awarded the Nobel Prize in physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them." The award recognized his early leading work in the emerging field of Quantum Mechanics.

While at Manchester University, Bohr had adapted Rutherford's nuclear structure to Max Planck's quantum theory and so obtained a model of atomic structure which, with later improvements – mainly as a result of Heisenberg's concepts – remains valid to this day. Bohr published his model of atomic structure in 1913. Here he introduced the theory of electrons traveling in orbits around the atom'snucleus, the chemical properties of each element being largely determined by the number of electrons in the outer orbits of its atoms. Bohr also introduced the idea that an electron could drop from a higher-energy orbit to a lower one, in the process emitting a photon (light quantum) of discrete energy. This became a basis for quantum theory.

Among the international community of nuclear physicists, Bohr came to play the role of convener of discussion groups and lectures, as well as being a mentor and an advisor. With the assistance of the Danish government and the Carlsberg Foundation, he succeeded in founding the Institute of Theoretical Physics in 1921, of which he became director. Bohr's institute served as a focal point for researchers into Quantum Mechanics and related subjects in the 1920s and '30s, when most of the world's best known theoretical physicists spent some time in his company. Bohr became widely appreciated as their congenial host and eminent colleague, both at the Institute and at the Foundation's mansion in Carlsberg, where he and his family resided after 1932.

Bohr also conceived the principle of complementarity: that items could be separately analyzed as having several contradictory properties. For example, physicists currently conclude that light behaves either as a wave or a stream of particles depending on the experimental framework – two apparently mutually exclusive properties – on the basis of this principle. Bohr found philosophical applications for this daring principle.^[specify] Albert Einstein much preferred the determinism of classical physics over the probabilistic new quantum physics (to which among many others Einstein himself had 'unwittingly' contributed). Philosophical issues that arose from the novel aspects of Quantum Mechanics became widely celebrated subjects of discussion. Einstein and Bohr had good-natured arguments over such issues throughout their lives. See article Bohr–Einstein debates.

Werner Heisenberg worked as an assistant to Bohr and university lecturer in Copenhagen from 1926 to 1927. It was in Copenhagen, in 1927, that Heisenberg developed his uncertainty principle, while working on the mathematical foundations of quantum mechanics. Heisenberg later became head of the German nuclear energy project. In April 1940, early in World War II, Germany invaded and occupied Denmark. In September 1941, Bohr was visited by Heisenberg in Copenhagen.

Michael Faraday

Michael Faraday, FRS (22 September 1791 – 25 August 1867) was an English chemist and physicist (or natural philosopher, in the terminology of the time) who contributed to the fields of electromagnetism and electrochemistry.

Faraday studied the magnetic field around a conductor carrying a DC electric current. While conducting these studies, Faraday established the basis for the electromagnetic field concept in physics, subsequently enlarged upon by James Maxwell. He similarly discovered electromagnetic induction, diamagnetism, and laws of electrolysis. He established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, and it was largely due to his efforts that electricity became viable for use in technology.

As a chemist, Faraday discovered benzene, investigated the clathrate hydrate of chlorine, invented an early form of the Bunsen burner and the system of oxidation numbers, and popularised terminology such as anode, cathode, electrode, and ion.

Although Faraday received little formal education and knew little of higher mathematics, such as calculus, he was one of the most influential scientists in history. Historians of science refer to him as the best experimentalist in the history of science. The SI unit of capacitance, thefarad, is named after him, as is the Faraday constant, the charge on a mole of electrons (about 96,485 coulombs). Faraday's law of induction states that magnetic flux changing in time creates a proportional electromotive force.

Faraday was the first and foremost Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a life-time position.

Albert Einstein kept a photograph of Faraday on his study wall alongside pictures of Isaac Newton and James Clerk Maxwell.

Faraday's earliest chemical work was as an assistant to Humphry Davy. Faraday specifically studied chlorine, discovering two new chlorides of carbon. He also made the first rough experiments on the diffusion of gases, a phenomenon first pointed out by John Dalton, the physical importance of which was more fully brought to light byThomas Graham and Joseph Loschmidt. He succeeded in liquefying several gases; he investigated the alloys of steel, and produced several new kinds of glass intended for optical purposes. A specimen of one of these heavy glasses afterwards became historically important as the substance in which Faraday detected the rotation of the plane of polarisation of light when the glass was placed in a magnetic field, and also as the substance that was first repelled by the poles of the magnet. He also endeavoured, with some success, to make the general methods of chemistry, as distinguished from its results, the subject of special study and of popular exposition.

Faraday was highly religious; he was a member of the Sandemanian Church, a Christian sect founded in 1730 that demanded total faith and commitment. Biographers have noted that "a strong sense of the unity of God and nature pervaded Faraday's life and work."

He invented an early form of what was to become the Bunsen burner, which is used almost universally in science laboratories as a convenient source of heat. Faraday worked extensively in the field of chemistry, discovering chemical substances such as benzene (which he called bicarburet of hydrogen), and liquefying gases such as chlorine. Liquification of gases helped establish that gases are simply the vapours of liquids possessing a very low boiling-point, and gave a more solid basis to conceptions of molecular aggregation. In 1820 Faraday reported on the first syntheses of compounds made from carbon and chlorine, C₂Cl₆ and C₂Cl₄, and published his results the following year. Faraday also determined the composition of the chlorine clathrate hydrate, which had been discovered by Humphry Davy in 1810.

Faraday also discovered the laws of electrolysis and popularised terminology such as anode, cathode, electrode, and ion, terms largely created by William Whewell.

Faraday is best known for his work with electricity and magnetism. His first recorded experiment was the construction of a voltaic pile with seven halfpence pieces, stacked together with seven disks of sheet zinc, and six pieces of paper moistened with salt water. With this pile he decomposed sulphate of magnesia (first letter to Abbott, 12 July 1812).In 1821, soon after the Danish physicist and chemist, Hans Christian Ørsted discovered the phenomenon ofelectromagnetism, Davy and British scientist William Hyde Wollaston tried but failed to design an electric motor. Faraday, having discussed the problem with the two men, went on to build two devices to produce what he called electromagnetic rotation: a continuous circular motion from the circular magnetic force around a wire and a wire extending into a pool of mercury with a magnet placed inside that would rotate around the magnet if supplied with current from a chemical battery. The latter device is known as a homopolar motor. These experiments and inventions form the foundation of modern electromagnetic technology. In his excitement, Faraday published results without acknowledging his work with either Wollaston or Davy. The resulting controversy within the Royal Society strained his mentor relationship with Davy and may well have contributed to Faraday’s assignment to other activities, thereby removing him from electromagnetic research for several years.Faraday's breakthrough came when he wrapped two insulated coils of wire around an iron^{[verification needed]} ring, and found that, upon passing a current through one coil, a momentary current was induced in the other coil.This phenomenon is known as mutual induction. The iron ring-coil apparatus is still on display at the Royal Institution. In subsequent experiments, he found that, if he moved a magnet through a loop of wire, an electric current flowed in the wire. The current also flowed if the loop was moved over a stationary magnet. His demonstrations established that a changing magnetic field produces an electric field. This relation was modelled mathematically by James Clerk Maxwell as Faraday's law, which subsequently became one of the four Maxwell equations. These in turn have evolved into the generalisation known today as field theory.

From his initial electromagnetic discovery in 1821, Faraday continued his laboratory work exploring properties of materials and developing the requisite experience. In 1824, Faraday briefly set up a circuit to study whether a magnetic field could regulate the flow of a current in an adjacent wire, but could find no such relationship. This lab followed similar work with light and magnets three years earlier with identical results. During the next seven years, Faraday spent much of his time perfecting his recipe for optical quality (heavy) glass, boro-silicate of lead, which he used in his future studies connecting light with magnetism. In his spare time from this optics work, Faraday continued publishing his experimental work (some of which related to EM) and conducted foreign correspondence with scientists (also working on EM) he previously met on his journeys about Europe with Davy. Two years after the death of Davy, in 1831, he began his great series of experiments in which he discovered electromagnetic induction. Joseph Henry likely discovered self-induction a few months earlier and both may have been anticipated by the work of Francesco Zantedeschi in Italy in 1829 and 1830.

Faraday later used the principle to construct the electric dynamo, the ancestor of modern power generators.

In 1839, he completed a series of experiments aimed at investigating the fundamental nature of electricity. Faraday used "static", batteries, and "animal electricity" to produce the phenomena of electrostatic attraction, electrolysis, magnetism, etc. He concluded that, contrary to scientific opinion of the time, the divisions between the various "kinds" of electricity were illusory. Faraday instead proposed that only a single "electricity" exists, and the changing values of quantity and intensity (current and voltage) would produce different groups of phenomena.

Near the end of his career, Faraday proposed that electromagnetic forces extended into the empty space around the conductor. This idea was rejected by his fellow scientists, and Faraday did not live to see this idea eventually accepted. Faraday's concept of lines of flux emanating from charged bodies and magnets provided a way to visualise electric and magnetic fields. That mental model was crucial to the successful development of electromechanical devices that dominated engineering and industry for the remainder of the 19th century.

Faraday was the first to report what later came to be called metallic nanoparticles. In 1847 he discovered that the optical properties of gold colloids differed from those of the corresponding bulk metal. This was probably the first reported observation of the effects of quantum size, and might be considered to be the birth of nanoscience.

Max Planck

Max Karl Ernst Ludwig Planck, ForMemRS, (April 23, 1858 – October 4, 1947) was a German physicist who is regarded as the founder of thequantum theory, for which he received the Nobel Prize in Physics in 1918.In Berlin, Planck joined the local Physical Society. He later wrote about this time: "In those days I was essentially the only theoretical physicist there, whence things were not so easy for me, because I started mentioning entropy, but this was not quite fashionable, since it was regarded as a mathematical spook". Thanks to his initiative, the various local Physical Societies of Germany merged in 1898 to form the German Physical Society (Deutsche Physikalische Gesellschaft, DPG); from 1905 to 1909 Planck was the president.

Planck started a six-semester course of lectures on theoretical physics, "dry, somewhat impersonal" according to Lise Meitner, "using no notes, never making mistakes, never faltering; the best lecturer I ever heard" according to an English participant, James R. Partington, who continues: "There were always many standing around the room. As the lecture-room was well heated and rather close, some of the listeners would from time to time drop to the floor, but this did not disturb the lecture". Planck did not establish an actual "school"; the number of his graduate students was only about 20, among them:

1897 Max Abraham (1875–1922)

1904 Moritz Schlick (1882–1936)

1906 Walther Meißner (1882–1974)

1906 Max von Laue (1879–1960)

1907 Fritz Reiche (1883–1960)

1912 Walter Schottky (1886–1976)

1914 Walther Bothe (1891–1957)

At the onset of the First World War Planck endorsed the general excitement of the public, writing that, "Besides much that is horrible, there is also much that is unexpectedly great and beautiful: the smooth solution of the most difficult domestic political problems by the unification of all parties (and) ... the extolling of everything good and noble."

Nonetheless, Planck refrained from the extremes of nationalism. In 1915, at a time when Italy was about to join the Allied Powers, he voted successfully for a scientific paper from Italy, which received a prize from the Prussian Academy of Sciences, where Planck was one of four permanent presidents.

Planck also signed the infamous "Manifesto of the 93 intellectuals", a pamphlet of polemic war propaganda (while Einstein retained a strictly pacifistic attitude which almost led to his imprisonment, being spared by his Swiss citizenship). But in 1915 Planck, after several meetings with Dutch physicist Lorentz, he revoked parts of the Manifesto. Then in 1916 he signed a declaration against German annexationism.

Mary Leakey

Mary Leakey (6 February 1913 – 9 December 1996) was a British archaeologist and anthropologist, who discovered the first skull of a fossil ape onRusinga Island and also a noted robust Australopithecine called Zinjanthropus at Olduvai. For much of her career she worked together with her husband, Louis Leakey, in Olduvai Gorge, uncovering the tools and fossils of ancient hominines. She developed a system for classifying the stone tools found at Olduvai. She also discovered the Laetoli footprints. In 1960 she became director of excavation at Olduvai and subsequently took it over, building her own staff. After the death of her husband she became a leading palaeoanthropologist, helping to establish the Leakey tradition by training her son, Richard, in the field.

Mary Leakey was born Mary Douglas Nicol on 6 February 1913 in London, England to Erskine Edward Nicol and Cecilia Marion (Frere) Nicol. Since Erskine worked as a painter, specializing in watercolor landscapes, the Nicol family would move from place to place, visiting numerous locations in France, Italy, and Egypt where Erskine painted scenes to be sold in England. Erskine Nicol developed an amateur enthusiasm for Egyptologyduring his travels. Mary Leakey was a direct descendant of antiquarian, John Frere, and cousin to archaeologist, Sheppard Frere, on her mother's side. The Frere family had been active abolitionists in the British colonial empire during the nineteenth century and established several communities for freed slaves. Three of these communities remained in existence as of Mrs. Leakey's 1984 autobiography: Freretown, Kenya,Freretown, South Africa, and Freretown, India. She also was a distant relative of baronet Henry Bartle Frere.

The Nicols spent much of their time in southern France. Mary became fluent in French. She identified more with the adventurous spirit of her father, going for long walks and explorations with him and having long talks. She disliked her governess and had less sympathy for her mother.

In 1925, when Mary was 12, the Nicols stayed at Les Eyzies at a time when Elie Peyrony was excavating one of the caves there. Peyrony did not understand the significance of much of what he found, and was not excavating scientifically during that early stage of archaeology. Mary received permission to go through his dump. It was there that her interest in prehistory was sparked. She started a collection of points, scrapers, and blades from the dump and developed her first system of classification.

That winter, the family moved to Cabrerets, a village of Dordogne, France. There she met Abbé Lemozi, the village priest, who befriended her and became her mentor for a time. The two toured Pech Merle cave to view the prehistoric paintings of bison and horses.

Mary Curie

Marie Skłodowska Curie (7 November 1867 – 4 July 1934) was a Polish–French physicist–chemist famous for her pioneering research onradioactivity. She was the first person honored with two Nobel Prizes—in physics and chemistry. She was the first female professor at theUniversity of Paris. She was the first woman to be entombed on her own merits (in 1995) in the Paris Panthéon.^{[citation needed]}

She was born Maria Salomea Skłodowska in Warsaw, in Russian Poland, and lived there to the age of 24. In 1891 she followed her older sister Bronisława to study in Paris, where she earned her higher degrees and conducted her subsequent scientific work. She shared her Nobel Prize in Physics (1903) with her husband Pierre Curie (and with Henri Becquerel). Her daughter Irène Joliot-Curie and son-in-law, Frédéric Joliot-Curie, would similarly share a Nobel Prize. She was the sole winner of the 1911 Nobel Prize in Chemistry. Curie was the first woman to win a Nobel Prize, and is the only woman to win in two fields, and the only person to win in multiple sciences.

Her achievements include a theory of radioactivity (a term that she coined), techniques for isolating radioactive isotopes, and the discovery of two elements, polonium and radium. Under her direction, the world's first studies were conducted into the treatment of neoplasms, using radioactive isotopes. She founded the Curie Institutes: the Curie Institute (Paris) and the Curie Institute (Warsaw).

In 1903 the Royal Swedish Academy of Sciences awarded Pierre Curie, Marie Curie and Henri Becquerel the Nobel Prize in Physics, "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel."

While an actively loyal French citizen, Skłodowska–Curie (as she styled herself) never lost her sense of Polish identity. She taught her daughters the Polish language and took them on visits to Poland. She named the first chemical element that she discovered "polonium" (1898) for her native country. During World War I she became a member of the Committee for a Free Poland (Komitet Wolnej Polski). In 1932 she founded a Radium Institute (now the Maria Skłodowska–Curie Institute of Oncology) in her home town, Warsaw, headed by her physician-sister Bronisława.

Skłodowska–Curie and her husband were unable to go to Stockholm to receive the prize in person, but they shared its financial proceeds with needy acquaintances, including students.

On receiving the Nobel Prize, Marie and Pierre Curie suddenly became very famous. The Sorbonne gave Pierre a professorship and permitted him to establish his own laboratory, in which Skłodowska–Curie became the director of research.

In 1897 and 1904, respectively, Skłodowska–Curie gave birth to their daughters, Irène and Eve Curie. She later hired Polish governessesto teach her daughters her native language, and sent or took them on visits to Poland.

Skłodowska–Curie was the first woman to be awarded a Nobel Prize. Eight years later, she would receive the 1911 Nobel Prize in Chemistry, "in recognition of her services to the advancement of chemistry by the discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element."

A month after accepting her 1911 Nobel Prize, she was hospitalized with depression and a kidney ailment.Skłodowska–Curie was the first person to win or share two Nobel Prizes. She is one of only two people who have been awarded a Nobel Prize in two different fields, the other person being Linus Pauling (for chemistry and for peace). Nevertheless, in 1911 the French Academy of Sciences refused to abandon its prejudice against women, and she failed by two votes to be elected a member. Elected instead was Édouard Branly, an inventor who had helped Guglielmo Marconi develop the wireless telegraph. It would be a doctoral student of Skłodowska–Curie, Marguerite Perey, who would become the first woman elected to membership in the Academy – over half a century later, in 1962.

Louis de Broglie

Louis-Victor-Pierre-Raymond, 7th duc de Broglie, FRS ( 15 August 1892 – Louveciennes, France, 19 March 1987) was a French physicist and a Nobel laureate in the year 1929. He was the sixteenth member elected to occupy seat 1 of the Académie française in 1944, and served as Perpetual Secretary of the Académie des sciences, France.

Louis de Broglie was born to a noble family in Dieppe, Seine-Maritime, younger son of Victor, 5th duc de Broglie. He became the 7th duc de Broglieupon the death without heir in 1960 of his older brother, Maurice, 6th duc de Broglie, also a physicist. He did not marry. When he died inLouveciennes, he was succeeded as duke by a distant cousin, Victor-François, 8th duc de Broglie.

De Broglie had originally intended a career in humanities, and received his first degree in history. Afterwards, though, he turned his attention toward mathematics and physics and received a degree in physics. With the outbreak of the First World War in 1914, he offered his services to the army in the development of radio communications.

His 1924 , Recherches sur la théorie des quanta (Research on the Theory of the Quanta), introduced his theory of electron waves. This included thewave-particle duality theory of matter, based on the work of Max Planck and Albert Einstein on light. The thesis examiners, unsure of the material, passed his thesis to Einstein for evaluation who endorsed his wave-particle duality proposal wholeheartedly; de Broglie was awarded his doctorate. This research culminated in the de Broglie hypothesis stating that any moving particle or object had an associated wave. De Broglie thus created a new field in physics, the mécanique ondulatoire, or wave mechanics, uniting the physics of energy (wave) and matter (particle). For this he won the Nobel Prize in Physics in 1929.

In his later career, de Broglie worked to develop a causal explanation of wave mechanics, in opposition to the wholly probabilistic models which dominate quantum mechanical theory; it was refined byDavid Bohm in the 1950s.

In addition to strictly scientific work, de Broglie thought and wrote about the philosophy of science, including the value of modern scientific discoveries.

De Broglie became a member of the Académie des sciences in 1933, and was the academy's perpetual secretary from 1942. On 12 October 1944, he was elected to the Académie française, replacing mathematician Émile Picard. Because of the deaths and imprisonments of Académie members during the occupation and other effects of the war, the Académie was unable to meet the quorum of twenty members for his election; due to the exceptional circumstances, however, his unanimous election by the seventeen members present was accepted. In an event unique in the history of the Académie, he was received as a member by his own brother Maurice, who had been elected in 1934. UNESCO awarded him the first Kalinga Prize in 1952 for his work in popularizing scientific knowledge, and he was elected a Foreign Member of the Royal Society on 23 April 1953. In 1961 he received the title of Knight of the Grand Cross in the Légion d'honneur. De Broglie was awarded a post as counselor to the French High Commission of Atomic Energy in 1945 for his efforts to bring industry and science closer together. He established a center for applied mechanics at the Henri Poincaré Institute, where research into optics, cybernetics, and atomic energy were carried out. He inspired the formation of the International Academy of Quantum Molecular Science and was an early member.

Lise Meitner

Lise Meitner FRS (7 or 17 November 1878 – 27 October 1968) was an Austrian-born, later Swedish, physicist who worked on radioactivity andnuclear physics. Meitner was part of the team that discovered nuclear fission, an achievement for which her colleague Otto Hahn was awarded theNobel Prize. Meitner is often mentioned as one of the most glaring examples of women's scientific achievement overlooked by the Nobel committee. A 1997 Physics Today study concluded that Meitner's omission was "a rare instance in which personal negative opinions apparently led to the exclusion of a deserving scientist" from the Nobel. Element 109, Meitnerium, is named in her honor.

Inspired by her teacher, physicist Ludwig Boltzmann, Meitner studied physics and became the second woman to obtain a doctoral degree in physics at the University of Vienna in 1905 ("Wärmeleitung im inhomogenen Körper"). Women were not allowed to attend institutions of higher education in those days, but thanks to support from her parents, she was able to obtain private higher education, which she completed in 1901 with an "externe Matura" examination at the Akademisches Gymnasium. Following the doctoral degree, she rejected an offer to work in a gas lamp factory. Encouraged by her father and backed by his financial support, she went to Berlin. Max Planck allowed her to attend his lectures, an unusual gesture by Planck, who until then had rejected any women wanting to attend his lectures. After one year, Meitner became Planck's assistant. During the first years she worked together with chemist Otto Hahn and discovered with him several new isotopes. In 1909 she presented two papers on beta-radiation.

In 1912 the research group Hahn-Meitner moved to the newly founded Kaiser-Wilhelm-Institut (KWI) in Berlin-Dahlem, south west in Berlin. She worked without salary as a "guest" in Hahn's department of Radiochemistry. It was not until 1913, at 35 years old and following an offer to go to Prague as associate professor, that she got a permanent position at KWI.

In the first part of the First World War (World War I), she served as a nurse handling X-ray equipment. She returned to Berlin and her research in 1916, but not without inner struggle. She felt in a way ashamed of wanting to continue her research efforts when thinking about the pain and suffering of the victims of war and their medical and emotional needs.

In 1917, she and Hahn discovered the first long-lived isotope of the element protactinium, for which she was awarded the Leibniz Medal by the Berlin Academy of Sciences. That year, Meitner was given her own physics section at the Kaiser Wilhelm Institute for Chemistry.

In 1922, she discovered the cause, known as the Auger effect, of the emission from surfaces of electrons with 'signature' energies. The effect is named for Pierre Victor Auger, a French scientist who independently discovered the effect in 1923.

In 1926, Meitner became the first woman in Germany to assume a post of full professor in physics, at the University of Berlin. There she undertook the research program in nuclear physics which eventually led to her co-discovery of nuclear fission in 1939, after she had left Berlin. She was praised by Albert Einstein as the "German Marie Curie".

In 1930, Meitner taught a seminar on nuclear physics and chemistry with Leó Szilárd. With the discovery of the neutron in the early 1930s, speculation arose in the scientific community that it might be possible to create elements heavier than uranium (atomic number 92) in the laboratory. A scientific race began between Ernest Rutherford in Britain, Irène Joliot-Curie in France, Enrico Fermi in Italy, and the Meitner-Hahn team in Berlin. At the time, all concerned believed that this was abstract research for the probable honour of a Nobel prize. None suspected that this research would culminate in nuclear weapons.

When Adolf Hitler came to power in 1933, Meitner was acting director of the Institute for Chemistry. Although she was protected by her Austrian citizenship, all other Jewish scientists, including her nephew Otto Frisch, Fritz Haber, Leó Szilárd and many other eminent figures, were dismissed or forced to resign from their posts. Most of them emigrated from Germany. Her response was to say nothing and bury herself in her work; she later acknowledged, in 1946, that "It was not only stupid but also very wrong that I did not leave at once."

After the Anschluss, her situation became desperate. In July 1938, Meitner, with help from the Dutch physicists Dirk Coster and Adriaan Fokker, escaped to the Netherlands. She was forced to travel under cover to the Dutch border, where Coster persuaded German immigration officers that she had permission to travel to the Netherlands. She reached safety, though without her possessions. Meitner later said that she left Germany forever with 10 marks in her purse. Before she left, Otto Hahn had given her a diamond ring he had inherited from his mother: this was to be used to bribe the frontier guards if required. It was not required, and Meitner's nephew's wife later wore it.

Meitner was lucky to escape, as Kurt Hess, a chemist who was an avid Nazi, had informed the authorities that she was about to flee. However, unknown friends only checked after they knew she was safe.^{[clarification needed]} An appointment at the University of Groningen did not come through, and she went instead to Stockholm, where she took up a post at Manne Siegbahn's laboratory, despite the difficulty caused by Siegbahn's prejudice against women in science. Here she established a working relationship with Niels Bohr, who travelled regularly between Copenhagen and Stockholm. She continued to correspond with Hahn and other German scientists.

James Chadwick

James Chadwick CH FRS (20 October 1891 – 24 July 1974) was an English Nobel laureate in physics awarded for his discovery of the neutron.

In 1932, Chadwick discovered a previously unknown particle in the atomic nucleus. This particle became known as the neutron because of its lack of electric charge. Chadwick's discovery was crucial for the fission of uranium 235. Unlike positively charged alpha particles, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements. For this discovery he was awarded the Hughes Medal of the Royal Society in 1932 and the Nobel Prize for Physics in 1935.

Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory. His discovery particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear reactions brought by slowed neutrons, and led Lise Meitner, Otto Hahn and Fritz Strassmann, German radiochemists in Berlin, to the revolutionary discovery of “nuclear fission”.

Chadwick became professor of physics at University of Liverpool in 1935. As a result of the Frisch–Peierls memorandum in 1940 on the feasibility of an atomic bomb, he was appointed to the MAUD Committee that investigated the matter further. He visited North America as part of the Tizard Mission in 1940 to collaborate with the Americans and Canadians on nuclear research. Returning to England in November 1940, he concluded that nothing would emerge from this research until after the war. In December 1940 Franz Simon, who had been commissioned by MAUD, reported that it was possible to separate the isotope uranium-235. Simon's report included cost estimates and technical specifications for a large uranium enrichment plant. James Chadwick later wrote that it was at that time that he "realised that a nuclear bomb was not only possible, it was inevitable. I had to then take sleeping pills. It was the only remedy."

He shortly afterward joined the Manhattan Project in the United States, which developed the atomic bombs dropped on Hiroshima and Nagasaki. Chadwick was knighted in 1945.

In 1940, Chadwick forwarded to the Royal Society the work of two French scientists, Hans Von Halban and Lew Kowarski, who worked in Cambridge. He asked that the papers be held as they were not appropriate for publication during the war. In 2007, the Society discovered the documents during an audit of their archives.

J.J Thomson

Sir Joseph John "J. J." Thomson, (18 December 1856 – 30 August 1940) was a British physicist and Nobel laureate. He is credited for the discovery of the electron and of isotopes, and the invention of the mass spectrometer. Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases.

Several scientists, such as William Prout and Norman Lockyer, had suggested that atoms were built up from a more fundamental unit, but they envisaged this unit to be the size of the smallest atom, hydrogen. Thomson, in 1897, was the first to suggest that the fundamental unit was over 1000 times smaller than an atom, suggesting the sub-atomic particles now known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that Lenard rays could travel much further through air than expected for an atomic-sized particle. He estimated the mass of cathode rays by measuring the heat generated when the rays hit a thermal junction and comparing this with the magnetic deflection of the rays. His experiments suggested not only that cathode rays were over 1000 times lighter than the hydrogen atom, but also that their mass was the same whatever type of atom they came from. He concluded that the rays were composed of very light, negatively charged particles which were a universal building block of atoms. He called the particles "corpuscles", but later scientists preferred the name electron which had been suggested by George Johnstone Stoney in 1894, prior to Thomson's actual discovery.

In April 1897 Thomson had only early indications that the cathode rays could be deflected electrically (previous investigators such as Heinrich Hertz had thought they could not be). A month after Thomson's announcement of the corpuscle he found that he could deflect the rays reliably by electric fields if he evacuated the discharge tubes to very low pressures. By comparing the deflection of a beam of cathode rays by electric and magnetic fields he was then able to get more robust measurements of the mass to charge ratio that confirmed his previous estimates. This became the classic means of measuring the charge and mass of the electron.

Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge; this was the "plum pudding" model—the electrons were embedded in the positive charge like plums in a plum pudding (although in Thomson's model they were not stationary, but orbiting rapidly).

In 1912, as part of his exploration into the composition of canal rays, Thomson and his research assistant F. W. Aston channelled a stream of ionized neon through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path. They observed two patches of light on the photographic plate (see image on right), which suggested two different parabolas of deflection, and concluded that neon is composed of atoms of two different atomic masses (neon-20 and neon-22), that is to say of two isotopes. This was the first evidence for isotopes of a stable element; Frederick Soddy had previously proposed the existence of isotopes to explain the decay of certain radioactive elements.

JJ Thomson's separation of neon isotopes by their mass was the first example of mass spectrometry, which was subsequently improved and developed into a general method by F. W. Aston and by A. J. Dempster.

Hermann von Helmholtz

Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist who made significant contributions to several widely varied areas of modern science. In physiology and psychology, he is known for his mathematics of theeye, theories of vision, ideas on the visual perception of space, color vision research, and on the sensation of tone, perception of sound, andempiricism. In physics, he is known for his theories on the conservation of energy, work in electrodynamics, chemical thermodynamics, and on amechanical foundation of thermodynamics. As a philosopher, he is known for his philosophy of science, ideas on the relation between the laws of perception and the laws of nature, the science of aesthetics, and ideas on the civilizing power of science. The largest German association ofresearch institutions, the Helmholtz Association, is named after him.His first important scientific achievement, an 1847 physics treatise on the conservation of energy was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying muscle metabolism. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no vital forcesnecessary to move a muscle. This was a rejection of the speculative tradition of Naturphilosophie which was at that time a dominant philosophical paradigm in German physiology.

Drawing on the earlier work of Sadi Carnot, Émile Clapeyron and James Prescott Joule, he postulated a relationship between mechanics, heat, light, electricity and magnetism by treating them all as manifestations of a single force (energy in modern terms). He published his theories in his book Über die Erhaltung der Kraft (On the Conservation of Force, 1847). Whether or not Helmholtz knew ofJulius Robert von Mayer's discovery of the law of conservation of energy in the beginning of the 1840s is a point of controversy. Helmholtz did not quote Mayer in his work and was accused by contemporaries of plagiarism.

In the 1850s and 60s, building on the publications of William Thomson, Helmholtz and William Rankine popularized the idea of the heat death of the universe.

Henri Becquerel

Antoine Henri Becquerel (15 December 1852 – 25 August 1908) was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.In 1892, he became the third in his family to occupy the physics chair at the Muséum National d'Histoire Naturelle. In 1894, he became chief engineer in the Department of Bridges and Highways. During the later half of his career Becquerel stayed in Clifton, Bristol while undergoing his investigations into the phosphorescence of uranium salts which was one of his most renowned discoveries.

In 1896, while investigating phosphorescence in uranium salts, Becquerel accidentally discovered radioactivity. Investigating the work of Wilhelm Conrad Röntgen, Becquerel wrapped a fluorescent substance, potassium uranyl sulfate, in photographic plates and black material in preparation for an experiment requiring bright sunlight. However, prior to actually performing the experiment, Becquerel found that the photographic plates were already exposed, showing the image of the substance. This discovery led Becquerel to investigate the spontaneous emission of nuclear radiation.
Describing his method to the French Academy of Sciences on 24 January 1896, he said:

One wraps a Lumière photographic plate with a bromide emulsion in two sheets of very thick black paper, such that the plate does not become clouded upon being exposed to the sun for a day. One places on the sheet of paper, on the outside, a slab of the phosphorescent substance, and one exposes the whole to the sun for several hours. When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative. If one places between the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out design, one sees the image of these objects appear on the negative. … One must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduces silver salts.

In 1903, he shared the Nobel Prize in Physics with Pierre and Marie Curie "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity".

Enrico Fermi

Enrico Fermi (29 September 1901 – 28 November 1954) was an an Italian-born, naturalized American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics. He was awarded the 1938 Nobel Prize in Physics for his work on induced radioactivity.

Fermi is widely regarded as one of the leading scientists of the 20th century, highly accomplished in both theory and experiment. Along withJ. Robert Oppenheimer, he is frequently referred to as "the father of the atomic bomb". He also held several patents related to the use of nuclear power.

In 1918 Fermi enrolled at the Scuola Normale Superiore in Pisa, where he was later to receive his undergraduate and doctoral degree. In order to enter the Institute, candidates had to take an entrance exam which included an essay. For his essay on the given theme Characteristics of Sound, 17-year-old Fermi chose to derive and solve the Fourier analysis based partial differential equation for waves on a string. The examiner, Prof. Giulio Pittato, interviewed Fermi and concluded that his essay would have been commendable even for a doctoral degree. Enrico Fermi achieved first place in the classification of the entrance exam. During his years at the Scuola Normale Superiore, Fermi teamed up with a fellow student named Franco Rasetti with whom he used to indulge in light-hearted pranks. Later, Rasetti became Fermi's close friend and collaborator. Besides attending the classes, Enrico Fermi found the time to work on his extracurricular activities, particularly with the help of his friend Enrico Persico, who remained in Rome to attend the university. Between 1919 and 1923 Fermi studied general relativity, quantum mechanics and atomic physics.

Several awards, concepts, and institutions are named after Fermi, such as the Enrico Fermi Award, the Enrico Fermi Institute, the Fermi National Accelerator Lab, the Fermi Gamma-ray Space Telescope, the Enrico Fermi Nuclear Generating Station, a type of particles called fermions, thesynthetic element Fermium, and many more.

His knowledge of quantum physics reached such a high level that the head of the Physics Institute, Prof. Luigi Puccianti, asked him to organize seminars about that topic. During this time he learned tensor calculus, a mathematical instrument invented by Gregorio Ricci and Tullio Levi-Civita, and needed to demonstrate the principles of general relativity. In 1921, his third year at the university, he published his first scientific works in the Italian journal Nuovo Cimento: the first was titled: On the dynamics of a solid system of electrical charges in transient conditions; the second: On the electrostatics of a uniform gravitational field of electromagnetic charges and on the weight of electromagnetic charges. At first glance, the first paper seemed to point out a contradiction between the electrodynamic theory and the relativistic one concerning the calculation of the electromagnetic masses. After one year with a work entitled Correction of severe discrepancy between electrodynamic theory and the relativistic one of electromagnetic charges. Inertia and weight of electricity, Enrico Fermi showed the correctness of his paper. This last publication was so successful that it was translated into German and published in the famous German scientific journal Physikalische Zeitschrift.

In 1922 he published his first important scientific work in the Italian journal I Rendiconti dell'Accademia dei Lincei entitled "On the phenomena that happen close to the line of time", where he introduces for the first time the so-called "Fermi coordinates", and proves that when close to the time line, space behaves as a euclidean one. In 1922 Fermi graduated from Scuola Normale Superiore.

In 1923, while writing the appendix for the Italian edition of the book The Mathematical Theory of Relativity by A. Kopff, Enrico Fermi pointed out, for the first time, that hidden inside the famous Einstein equation (E = mc²), there was an enormous amount of nuclear potential energy to be exploited.

Fermi's Ph.D advisor was Luigi Puccianti. In 1924 Fermi spent a semester at the University of Göttingen, and then stayed for a few months in Leiden with Paul Ehrenfest. From January 1925 to the autumn of 1926, he stayed at the University of Florence. In this period he wrote his work on the Fermi–Dirac statistics.