# Julian Schwinger

Julian Seymour Schwinger (February 12, 1918 – July 16, 1994) was an American theoretical physicist. He is best known for his work on quantum electrodynamics (QED), in particular for developing a relativistically invariant perturbation theory, and for renormalizing QED to one loop order.
Schwinger is recognized as an important physicist, responsible for much of modern quantum field theory, including a variational approach, and the equations of motion for quantum fields. He developed the first electroweak model, and the first example of confinement in 1+1 dimensions. He is responsible for the theory of multiple neutrinos, Schwinger terms, and the theory of the spin-3/2 field. Schwinger was jointly awarded the Nobel Prize in Physics in 1965 for his work on quantum electrodynamics (QED), along with Richard Feynman and Shin'ichirō Tomonaga.

## Quotes

* Time appears in quantum mechanics as a continuous parameter which represents an abstraction of the dynamical role of the measurement apparatus. The requirement of relativistic invariance invites the extension of this abstraction to include space and time coordinates. The implication that space-time localized measurements are a useful, if practically unrealizable idealization may be incorrect, but it is a grave error dismiss the concept on the basis of a priori notions of measurability.
** "Relativistic Quantum Field Theory, Nobel Lecture, December 11, 1965". Nobel Lectures, Physics 1963-1970. Amsterdam: Elsevier Publishing Company. 1972. pp. 140–152. (quote from p. 142)
* If my history lesson has done nothing else, it should have reminded you that, during any given period in the evolving history of physics, the prevailing, main line, climate of opinion was likely as not to be wrong, as seen in the light of later developments. And yet, in those earlier times, with relatively few individuals involved, change did occur, but slowly... What is fundamentally different in the present day situation in high energy physics is that large numbers of workers are involved, with corresponding pressures to conformity and resistance to any deflection in direction of the main stream, and that the time scale of one scientific generation is much too long for the rapid pace of experimental discovery. I also have a secret fear that new generations may not necessarily have the opportunity to become familiar with dissident ideas.
** as quoted by Sameer Shah in "If you can't join 'em, beat 'em": Julian Schwinger's Conflicts in Physics. Directions in Cultural History, The UCLA Historical Journal, Volume 21, 2005-2006, p. 50
* Perhaps the most important contribution to science that the Royal Society has made in its three centuries of existence is its early role in publishing Newton's masterful account of his discoveries: Mathematical Principles of Natural Philosophy—the Principia.
** Einstein's Legacy: The Unity of Space and Time (2002) p. 2
* Is the purpose of theoretical physics to be no more than a cataloging of all the things that can happen when particles interact with each other and separate? Or is it to be an understanding at a deeper level in which there are things that are not directly observable (as the underlying quantized fields are) but in terms of which we shall have a more fundamental understanding?
** Quantum Mechanics - Symbolism of Atomic Measurements (2001) p. 24 f.

## Quotes about Schwinger

* For two years in the late 1950s I was a postdoc at Harvard. Julian Schwinger was the leading light in theoretical physics at the time. We, the postdocs and junior faculty, audited whatever course he happened to be teaching. The material was always original. The lectures were on Wednesdays, and afterward the small group of us would have lunch with Schwinger at Chez Dreyfus in Cambridge. We would be joined by another small group from MIT that included Vikki Weisskopf. If Schwinger had any new ideas, he would try them out on Weisskopf. As it happened on this occasion, he had developed a “theory of everything.” Some of this theory survives in the work of other people. In 1962, he published a paper on “Gauge invariance and mass.”$^9$ … In it he raised the question of whether one could have a massive vector meson in a theory that had an underlying gauge invariance. This possibility … inspired P. W. Anderson to use these ideas in condensed matter physics.$^{10}$... 9 J. Schwinger, “Gauge invariance and mass,” Phys. Rev. 125, 397–398 1962 . 10 P. W. Anderson, “Plasmons, gauge invariance and mass,” Phys. Rev. 130, 439–442 1963.
** Jeremy Bernstein, (January 2011)"A question of mass". American Journal of Physics 79 (1): 25–31. DOI:10.1119/1.3487939. (quote from p. 30)
* During this period I attended two sessions of the Michigan summer school at which Schwinger (1948) and Feynman (1949) described their respective reformulations of QED. Schwinger’s was deeper and more complete while Feynman’s was easier to use but at that time incomplete. One may give a feeling for the impact of Schwinger by quoting Dyson who wrote home that ”in a few months we shall have forgotten what pre-Schwinger physics was like.” Bethe at that time described this period as the most exciting in physics since the great days of 1925-30 when quantum mechanics was being discovered.
** Robert Finkelstein: (2016). "My Century of Physics". arXiv preprint arXiv:1612.00079.

### Sheldon Glashow - The Origins Podcast (Mar 14, 2020)

    with Lawrence Krauss - FULL VIDEO Quotes are by Sheldon Glashow.
* It's true that he had a funny style. His lecture was precise. He had the voice of a radio announcer. Everything was in perfect sentences, grammatically perfect. The formulas were all clearly written on the board. The talk was so designed that he would be at the blackboard nearest the exit door at the end of the lecture. He would end the lecture and... immediately slip out the door and disappear so that his graduate students could not track him down too easily.
* He argued to me that electrons and muons, which are particles, charged leptons we call them, were known... He said that if we're going to have a quantum number that distinguishes electrons from muons, then surely... it should not be e$^-$ and μ$^-$ that have... lepton number, it should be the e$^-$ and the μ$^+$. So... that way... charge and the new quantum number can distinguish electrons from muons... and it followed that there had to be two kinds of neutrinos in nature. So built into the way he taught... particle physics was the fact that there are two kinds of neutrinos. ...It was acknowledged as a technical possibility by some people, but it... wouldn't be known until 1963. This was in the 1950s.
* So in 1958 when I went for my thesis exam... and Yang... was in my committee, he and Paul [C.] Martin and Julian Schwinger... I started explaining how the electron neutrino is different from the muon neutrino and Yang said, "Wait a minute... there's no way of distinguishing electron neutrinos from muon neutrinos. It makes no sense to say they are different from one another. It's a meaningless concept." ...I began to explain and Schwinger, seeing my distress and realizing that he was the cause... said, "Let me explain the situation to Mr. Yang" and he patiently explained how an experiment could be done, namely the experiment that would be done in a couple of years... to distinguish electron neutrinos from muon neutrinos, if... they were different... and Yang nodded and the exam continued and I passed the exam. ...[S]ix months later Lee and Yang published a paper explaining how electron neutrinos and muon neutrinos could be different from one another. They simply stole the idea from Julian. He was subject to many such acts of thievery. Years later I met Yang in China... and I described the incident to him... He said, "It is exactly as you said, Shelly."
** Note: Yang Chen-Ning & Tsung-Dao Lee, "Question of Parity Conservation in Weak Interactions" (1956) laid the groundwork for the concept of parity violation in the weak force, indirectly suggesting the possibility of distinct neutrino types based on their interactions with other particles. Bruno Pontecorvo "Electron and Muon Neutrinos" (1959) argued that the electron neutrino (ν$_e$) and the muon neutrino (ν$_μ$) were different particles. Ref: Pontecorvo and neutrino physics (2013)
* Schwinger had... been working on radar and solved some radar related... electrodynamic problems, classical electrodynamic theory problems that nobody else could approach... [A]s a calculator he was amazing... phenomenal. ...You can well argue that radar... as well as new developments in bomb technology, in fuses, played a more important role than nuclear weapons [in World War II].