Dirac: A Scientific Biography 1st Edition by Helge Kragh (PDF)

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This first full-length biography of Paul Adrien Maurice Dirac offers a comprehensive account of his physics in its historical context, including less known areas such as cosmology and classical electron theory. It is based extensively on unpublished sources, including Dirac’s correspondence with Bohr, Heisenberg, Pauli, Schrödinger, Gamow and others. Dirac was undoubtedly one of the most brilliant and influential physicists of the twentieth century. Between 1925 and 1934, the Nobel Prize laureate revolutionized physics with his brilliant contributions to quantum theory. This work examines Dirac’s successes and failures, and pays particular attention to his opposition to modern quantum electrodynamics; an opposition based on aesthetic objections.

User’s Reviews

Editorial Reviews: Review “…a delightful and instructive evocation of a remarkable human being by way of a judicious and documented passage downstream following the flow of modern physics.” Scientific American”…an important, highly professional contribution to the history of quantum theory.” Science”The entire biography is harmonic and a very interesting work created from previously unpublished documents.” Physics in Canada”One of the valuable features of Kragh’s fine if impersonal biography is that he dispels the myths surrounding Dirac and paints a portrait that clearly indicates Dirac’s limitations without diminishing his greatness.” Physics Today”This `scientific biography’ should be widely read by physicists.” Walter J. Moore, American Historical Review”The text has accounts of his life and extraordinary character with outlines of his achievements skilfully interwoven.” N. Kemmer, Nature”…will be most appreciated by those readers already acquainted with the relevant physics and, moreover, something of its historical development.” Peter R. Law, Mathematical Reviews Book Description The first full length biography of Dirac, one of the most brilliant physicists of the twentieth century.

Reviews from Amazon users which were colected at the time this book was published on the website:

⭐This is the best biography of Dirac that I have encountered. It concisely describes Dirac’s many contributions to physics, his philosophical outlook, and aspects of his interesting and unique personality. This book also contains an excellent selection of photographs.

⭐These are different and partially complementary biographies of the great English physicist Paul Dirac. Kragh’s biography is definitely, as the title states, a scientific biography. While the book contains all the basic biographical information, Kragh focuses on the development and significance of Dirac’s scientific work. This is a very technical account which is really only readable by those with a pretty sophisticated knowledge of the relevant physics. While undoubtedly accurate, Kragh’s book is not useful for general readers, even those with some general knowledge of the topic. This is a pity because Kragh has shown in other books that he is quite good at describing complex topics in lay terms.Farmelo’s book is a more conventional and chronologically arranged biography concentrating on Dirac as a person. Farmelo is a theoretical physicist who later became involved in science education and does a reasonable job of explaining the basics of Dirac’s work. I would have preferred significantly more emphasis on the science and its background but these aspects of Farmelo’s biography are certainly adequate. Farmelo shines with his narrative of Dirac’s life and career, particularly his rather unusual personality. Farmelo is also very good on the academic and intellectual environment around Dirac, both his home institution, Cambridge, and the international community of physicists of which Dirac was a very important member.Farmelo’s well written book has become somewhat well known for Farmelo’s well supported proposal that Dirac had a mild form of autism. Farmelo suggests also that aspects of Dirac’s autism, notably his obsessive behavior (though Farmelo does not use that term specifically) contributed to Dirac’s success as a theoretician. This is a reasonable suggestion. Both Kragh and Farmelo have very good and somewhat complementary discussions of Dirac’s conviction that mathematical beauty should play an important role in the development of theories.The ideal biography of Dirac would include the type of human detail and narrative found in Farmelo’s biography and at least some of the more detailed scientific explanation found in Kragh’s book. A better framing of Dirac’s work in the context of the marked changes in 20th century physics in which he participated would be welcome. If you want to read one book about Dirac or if you’re a non-physicist, read Farmelo. If you have the suitable background in physics, read both.

⭐I like this book because it emphasizes how much physics has changed since the beginning of the 20th century, shifting from the European tradition of natural philosophy that dealt with deep questions to the pragmatic approach in the US that fosuced on models that merley describe. My favorite passage (among many others) is (p.166):Bohr, Dirac, Pauli, Heusenberg, Born, Oppenheimer, Peierls and Fock came to the conclusion, each in his own way, that the failure of quantum electrodynamics at high energies would rquire a revolutionary break with current theory […] The pragmatic approach of the “quantum engineers”, including Fermi, Bethe, Heitler and a growing number of young American physicists, proved to be of significant value, but could not eliminate the fundamental problems that conmtinued to worry Dirac, Pauli and others.With the rcognition of the new particles (mesons) in the cosmic radiation, the existing theory – gradually improved in its details but noit changed in its essence – proved to be quite workable after all. The empirical disaagreements became less serious, and by the end of the thirties most young theorists had learned to live with the theory they adapted themselves to the new situation without caring too much about the theorys lack of consistency and conceptual clarity […] In 1947, revelation came after many years of trouble; when the modern theory of renormalization was established after the war, the majority of physicsits agreed that everything was fine and the long-awaited revolution was unnecessary…For anyone who wants to seriously evaluate the current state of physics, this is strong stuff.

⭐Dirac (1902-1984) shared with Schroedinger the 1933 Nobel prize for Physics “for the discovery of new productive forms of atomic theory” (as stated by the Nobel prize committee). He is one of the great 20-th century physicists and founders of quantum mechanics. His scientific contributions are discussed in good depth by Kragh while the aspects concerned with his personal life are mentioned on a more superficial level. Dirac’s scientific life lasted for over half a century: after the mandatory retirement from the University of Cambridge (where he was the holder of the Lucasian Chair of Mathematics until 1969) he moved to the United States where he spent the last years of his life working at the University of Miami and Florida State University.An analysis of Dirac’s approach to theoretical physics is discussed in the last part of the book: he was convinced that physics should be based on beautiful theories. This viewpoint, however, has been criticized by other physicists because some times a beautiful theory is not necessarily useful or in agreement with experiments. It appears reasonable to say, however, that mathematical beauty represents a good guide in the discovery of novel equations such as the relativistic equation that Dirac discovered in 1928.Dirac wrote the influential book The Principles of Quantum Mechanics (the 4-th edition appeared in 1958 and from then onward it has been reprinted many times) which is still an important text for those wishing to enter into the strange world of quantum mechanics. A book that well complements Kragh’s biography is The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom by Farmelo.

⭐Probably the most influential text on the new approach was “The Principles of Quantum Mechanics” by Paul Adrien Maurice Dirac (1902-1984) in 1930. Its title was deliberately chosen to allude to the world-famous text by Dirac’s predecessor as Lucasian professor of mathematics at Cambridge, i.e. Isaac Newton. Dirac himself was “The Strangest Man” (to quote a very readable biography by Graham Farmelo of this very singular individual), who always did his original thinking alone, was notoriously taciturn and introverted. This text influenced thousands, including the present reviewer who read it privately as an 2nd year undergraduate. There is minimal historical context in the book which begins with two significant admissions: 1) the inability of Classical Mechanics (CM) to explain the new experimental discoveries; 2) the inadequacies of the EM forces to explain the stability of atoms (the unadmitted starting point of Bohr’s theory). The heart of Dirac’s thinking here is his confusion on the meaning of the ‘state’ of an atomic system: implying a close analogy with CM’s mathematical view of a single system. Indeed, his whole theory was developed around a mathematical similarity he noticed between differences of derivatives of pairs of particle variables (location and momentum), called Poisson Brackets and differences of quantum variables (actually matrices or differential operators), he called quantum commutators. So, Dirac simply postulates a relationship between the two sets introducing Planck’s Action Quantum. He calls this vital step, the method of Classical Analogy, recognizing this introduces the failure of the commutative law of multiplication exhibited by ordinary numbers and standard algebra. He even fails to acknowledge this key insight came from his lifelong friend, Heisenberg but later, he does write that “the first form of QM was discovered by Heisenberg in 1925,” (which actually set Dirac off on his own lifelong study of QM).With his usual admirable honesty, Dirac concludes his masterpiece with the admission that: “The difficulties, being of a profound character, can removed only by some drastic change in the foundations of the theory, probably a change as drastic as the passage from Bohr’s orbit theory to the present quantum mechanics.” Dirac spent the next 50 years of his dedicated life unsuccessfully pursuing this vision; it has also inspired the present reviewer on a similar quest. Dirac’s work provides the mathematical details needed to master Quantum Mechanics (QM) but very little history. It is not recommended for the general reader but essential for many professional physicists.

⭐Helge Kragh, Professor am Centre for Science Studies der Universität Aarhus, arbeitet auf dem Gebiet der Geschichte von Wissenschaft und Technologie, sein vorliegendes Werk ist eine wissenschaftliche Biographie von Paul Dirac, einem der Wegbereiter die modernen Quantenmechanik, der aber, im Gegensatz zu Heisenberg, Pauli, Jordan und Schrödinger, eher unbemerkt von der Öffentlichkeit seine Arbeiten schuf.Wiewohl bereits kurz nach Diracs Tod, 1984, erste Dirac gewidmete Denkschriften erschienen, versucht der Autor hier ein umfassenderes, kohärentes Bild von Diracs Leben und seinen Beiträgen zur Wissenschaft zu zeichnen, wobei Diracs wissenschaftliche Erkenntnisse, ihre Bedeutung und Rezeption, deutlich im Vordergrund liegen – seine Lebensumstände bieten dabei eher den Rahmen, um Diracs akademischen Werdegang und die Hintergründe seiner Ideen besser einzuordnen und verstehen zu können. Kraghs Darstellung berücksichtigt alle Lebensabschnitte, auch die späteren Abschnitte, ab Dirac bereits abseits des Mainstreams der Physik arbeitete, ohne dabei Anspruch auf Vollständigkeit zu erheben.Paul Dirac begann zunächst ein Elektroingenieur- Studium in Bristol, wechselte dann aber zur Mathematik, und erhielt schließlich ein Stipendium für ein Graduiertenstudium in Cambridge, dort wurde Ralph Fowler sein Betreuer, der ihm 1925 den Probedruck von Heisenbergs fundamentaler Arbeit zum Durchbruch zur neuen Quantenmechanik zeigte; Dirac fand diese zunächst recht unzugänglich, stolperte dann aber über Heisenbergs, eher beiläufige Bemerkung, dass die dynamischen Größen der neuen Mechanik nicht kommutativ seien, d.h. nichttriviale Kommutatoren hätten – Dirac kam auf die zündende Idee, dass damit etwas Wesentliches verbunden sein müsse, und er erkannte, dass die Kommutatoren Analoga zu den Poisson- Klammern der klassischen Mechanik sind. Diese Verbindung inspirierte ihn, so dass er kurzer Hand eine eigene Version der Quantenmechanik ausarbeitet. Diese Theorie arbeitete Dirac in den folgenden Jahren zu einer allgemeinen Transformations Theorie nicht- kommutieren Größen (q- numbers) aus, und konnte damit die Äquivalenz von Heisenbergs Matrizen und Schrödingers Theorie zeigen.Seinen größten wissenschaftlichen Durchbruch erzielte Dirac aber mit der Formulierung der Gleichung der relativistischen Quantenmechanik, die auf dem eleganten mathematischen ‘Trick’ beruht, Matrizen zu betrachten, mit mit deren Hilfe Dirac die ‘Quadratwurzel’ des Hamilton Operators bilden konnte. Aus dieser neuen Gleichung folgte ganz zwanglos, dass Elektronen einen Spin besitzen müssen.Nachdem die neue Quantenmechanik etabliert war, musste diese sich auch an Strahlungsphänomenen bewähren, insbesondere musste man verstehen, wie mit ihrer Hilfe die Resultate von Planck, Ehrenfest und Einstein zur Strahlung Schwarzer Körper rigoros ableiten konnte. Auch dazu leistete Dirac wesentlich Beiträge; allerdings erwies sich die konsistente Formulierung einer Quantenfeld Theorie, die gleichermaßen elektromagnetische Felder und Elektronen beschreiben konnte, als weit schwieriger als ursprünglich gedacht. Betrachtete auch nur einfachste Problem, ergaben sich Lösungen, die allerlei unendliche Terme und Divergenzen enthielten.Diracs beeindruckende Resultate, ließen auch seine wissenschaftliche Karriere rasch voranschreiten, 1930 wählte ihn die Royal Society zu ihrem Mitglied (Fellow), 1932 wurde er auf den Lucasischen Lehrstuhl in Cambridge berufen, den vor ihm u.a Newton innehatte, und 1933 wurde er, gemeinsam mit Erwin Schrödinger, mit dem Nobelpreis geehrt; im gleichen Jahr erhielt Werner Heisenberg rückwirkend den Nobelpreis für das Jahr 1932.Den zweiten Teil widmet der Autor Diracs späten Jahren, 1934 – 84, Dirac war in zunehmenden Maße unzufrieden mit dem Zustand der QED, insbesondere war er der Ansicht, dass die erfolgreiche Anwendung der Renormierungs Methoden nicht darüber hinweg täuschen dürften, dass die eigentlichen Probleme des Auftretens von Divergenzen, weiterhin nicht verstanden wären. Er wandte sich vom Mainstream der Physik ab, hin zu eigenen Themen – von denen der Autor Diracs Arbeiten zum klassischen Elektron, zu magnetischen Monopolen und zur Kosmologie, in den folgenden Kapiteln näher beleuchtet. Dirac genoss ausgedehnte Vortragsreisen, die ihn u.a. in die USA, nach Japan, Indien, Frankreich und Deutschland führten. Nach seine Emeritierung zog er dauerhaft nach Florida, und nahm 1971 eine Stelle an der Florida State University in Tallahassee an – auch in dieser Periode blieb Dirac wissenschaftlich ungebrochen produktiv.Selbst wenn man die Maßstäbe der Gemeinschaft genialer Physiker anlegt, dürfte Dirac daraus hervorgestochen haben – ausgesprochen wortkarg, wurde Dirac Protagonist zahlloser skurriler Anekdoten, die gerade Bohr gern erzählte: Bei einem seiner Vorträge, warf einer der Hörer ein ‘die Ableitung diese Formel versehe ich nicht…’, Dirac stockte kurz, um dann ungerührt fortzufahren, worauf ihn der Moderator unterbrach ‘Prof. Dirac, können sie bitte auf die Frage eingehen…’, worauf Dirac antwortet: ‘welche Frage? – das war eine Feststellung’. Auf diese und andere menschliche Eigenheit geht Kragh in einem der letzten Kapitel ein. Abschließend erörtert der Autor Diracs allgemeine Ansichten zur Philosophie der Physik; dabei interessierte sich Dirac kaum für Philosophie im eigentlichen Sinn, in seinen späteren Jahren, reflektierte Dirac, den stets vor allem die fundamentalen Aspekte der Physik begeisterten, über philosophische Prinzipien, die ihn bei seiner Arbeit beschäftigten. Eine immer wiederkehrende Rolle spielt das Prinzip der mathematischen Schönheit, das Dirac etwa bei der Aufstellung seiner relativistischen Gleichung der QM geleitet hat – jedenfalls ist das seine Ansicht aus späterer Erinnerung, dabei war Dirac keineswegs ein mathematischer Purist, wie seine Umgang mit der Delta- Funktion bei der Grundlegung der QM zeigt.In seiner vorliegenden Biographie, vereinigt Helge Kragh eine wohldurchdachte Auswahl aus Diracs wissenschaftlichen Publikationen, sowohl aus seinen Hauptarbeiten zu den Fundamenten der Quantenmechanik, als auch auch aus seinen weniger bekannten Arbeiten aus späterer Zeit; er vermittelt dem Leser einen Eindruck von der kreativen Vielfalt Diracs originären Ideen.Die vor- relativistischen quantenmechanischen Arbeiten Diracs werden sehr ausführlich in dem Standardwerk von Mehra und Rechenberg zur Geschichte der Quantentheorie, Volume 4 Part 1, diskutiert. Eine wunderbare literarische Biographie Dirac findet man in ‘The Strangest Man’ (dt. ‘Der seltsamste Mensch’), Graham Farmelo berichtet darin akribisch über Diracs Leben, an Hand von zahllosen Zeitdokumenten, z.T. familiären Briefen, Interviews u.v.a. mehr.

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