Gautam Ramasubramanian MHC 20301 - Science and Technology at NYC Professor Lampousis 5 December 2014

Schwinger - The Lecturer, The Researcher and The Winner

Julian Schwinger had a particular perspective on lecture-giving. When he taught physics at Harvard, he often spent hours the night before preparing his lectures, down to the wording and movement, and considered the lecture as a self-contained piece of art. Rather than merely conveying material, Schwinger viewed the lecture as a presentation of a story, a self-contained cohesive experience that shone like artwork. One advantage of this is was the artistry in and of itself - students and faculty from neighboring colleges such as MIT would clamor into Harvard to sit through Schwinger’s lectures. The second advantage is that Schwinger would rephrase the same concept in multiple ways, allowing students to better retain the information. Yet, this approach had its problems. Questions from the audience were never welcomed, and his answers to them were rather terse and unsatisfactory. According to Mehra and Milton,

“[If] a questioner grew more and more persistent, [it] ...drew no response from Schwinger except for him ‘getting quieter and quieter and looking down at his feet,’ until the questioner gave up in embarrassment.”

Some students complained of Schwinger making very big logical jumps in the spirit of his flow, logical conclusions that were difficult for students to follow. Yet, the students who were able to follow praised his lecture style for its rigor and artistic flow. Schwinger was a theoretical physicist, one whose focus was on the field of quantum electrodynamics, the unification of the fields of special relativity and quantum theory. He won the Nobel Prize on his work on quantum electrodynamics in 1965 along with physicists Shin- Itiro Tomonaga and Richard Feynman (NobelPrize). Schwinger became interested in science when he was 10; at that time he wanted to become an engineer. It wasn’t too long before he realized that his true passion was physics. In high school, he wrote his first paper on quantum electrodynamics, in which he interpreted and tried to extend physicist Paul Dirac’s work on the subject. When he came to City College, news of his genius spread to the graduate students and then to Columbia University, where it caught the attention of Professor Isidor I. Rabi. Rabi, as an experimental physicist in Columbia, praised Julian’s ability to produce predicted measurements in his papers so that experimental physicists could verify (Milton, 2006). He was very impressed with Julian’s work, so much so that he got Schwinger transferred to Columbia. At Columbia, Julian was able to progress very fast. Within two years, he had published 8 papers, completed both undergraduate and graduate degrees and almost finished his doctoral thesis. He got his doctoral degree in 1939, and went to work under Robert Oppenheimer in UCLA Berkeley, where he worked on a number of specific research projects with visiting faculty. Examples include the Rarita-Schwinger Equations and the effects of tensor forces on nucleon magnetic and quadrupole moments (Martin & Glashow). When World War 2 came about, he was offered to work on the Manhattan Project by Robert Oppenheimer, a offer he decline in favor for working in the Radiation Lab at MIT to develop the microwave radar. He had several reasons for his choice (Milton, 2008). Firstly, he had less scruples on his conscience working on radar than working on the atomic bomb. Secondly, the theoretical foundations of microwave radiation was more interesting to him than nuclear fission. Finally, he was allowed to work independently at MIT, and he preferred that to constant collaboration. By choosing to work at MIT, he developed an affinity to relatively new mathematical objects that would serve him well in the future, such as Green’s functions and the application of Maxwell’s equations to waveguides. After the war, he received offers to teach at many top universities, and he elected to go to Harvard. It was in Harvard where he delved into the subject he only touched in that past, Quantum Electrodynamics and did groundbreaking work that would lead to the Nobel Prize. Quantum Electrodynamics is a field of physics which unified the theory of relativity and quantum mechanics, the two major fields that opened up during the early 20th century. Relativity described the properties of very fast objects, say objects moving close to the speed of light, or light itself. Quantum Mechanics, on the other hand, described the strange behavior of small particles, small as an electron. These theories were developed separately, but had a lot of common ground, and it was no strange matter that physicists tried to unify them. Quantum Electrodynamics was born from that unification process. Q.E.D. deals with the interaction between the photon (packets of light) and the electron. The first postulate of Q.E.D. states that electrons and photons are particles. Yet, if this particle were to go from point A to point B, the exact path the particle takes cannot be determined exactly. Thus, physicists have to compute probabilities of an electron taking each and every possible path from A to B and sum all those probabilities together to get weighted average, the path the particle is most likely to go (Feynman). Thus, when electrons are continuously shot at a wall with two openings, those that went through would form an wave-like interference pattern, a pattern that would be impossible if every electron had a definite path that went through either one of those two openings. The second postulate of Q.E.D. states that every physical system or interaction could be broken down to the three basic actions (Feynman). Firstly, an electron can move from point A to point B. (How it does that is computed by summing probabilities). Secondly, a photon moves from point A to point B (The path is computed also by summing probabilities). Finally, an electron can emit and/or absorb a photon, which causing a change in the electron’s direction in space and time. Q.E.D. has its foundations in these postulates, but its body is heavily reliant on mathematical theory, which Julian Schwinger played a large part in formulating. The development of Q.E.D. preceded Schwinger, but it was Schwinger who revised the mathematics behind the theory to make it compatible with physical experiments. When a new physical model is introduced to explain physical phenomena, that model is critiqued by haw well it could predict the results of experiments. Before Schwinger, Q.E.D. was very attractive from a theoretical standpoint, but failed to produce accurate predictions for experiments. In fact, the predictions would often turn out to be infinity. Since nothing in the physical world is infinite, the presence of these infinities in the mathematical body of Q.E.D. caused the subject to not be taken seriously by the physics community. Julian Schwinger, during his time at Harvard, worked with Richard Feynman on revising the mathematics behind Q.E.D. so that it would better predict phenomena in the real world. In this way, Schwinger discovered the process of renormalization. Renormalization referred to the mathematical manipulations required to remove many of the infinites which lurk within the math. Schwinger and Feynman removed many of the infinities within the body of Q.E.D., and the resulting theory was very accurate in providing accurate predictions for experiments, something experimental physicists can verify. Julian Schwinger and Richard Feynman both came up with the renormalized Q.E.D. in partnership. In Japan, a physicist named Shin-Itiro Tomonaga developed his own renormalization of Q.E.D. independently. Eventually, Schwinger and Tomonaga shared their ideas and worked together, and eventually all three of them received a Nobel prize for this achievement. Although it would seem that Julian Schwinger lived only for physics, his interests were actually very diverse. These interests got to express themselves more prominently when he married Clarisse Carroll, a marriage that held until his death 47 years later. It is interesting to note that during his bachelor days, he would have a fascination for chocolate ice cream and steak, and before his marriage and even for a while afterward, he would literally eat nothing else. However, Julian would travel a lot with his wife, and during his travels, he learned to be more flexible with his food habits. Julian was a cat lover, and during his time at Harvard, he and his wife owned a cat named Galileo, whom they had for 14 years. Julian was slightly overweight, but soon learned to exercise regularly and develop a liking for tennis and swimming. He was an ardent Mozart fan and his favorite piece was the “Marriage of Figaro” (Mehra & Milton). Julian continued teaching at Harvard for almost 40 years, until disagreements with colleges plus health issues caused him to move to California and teach at UCLA, Los Angeles (Milton, 2006), where he continued to teach and conduct research until the end of his life in 1995. His legacy is still carried on by his PhD students (Julian had numerous), some of whom went on to win Nobel prizes themselves, while others still work to this day on projects initiated by Schwinger. His own contribution to physics ranks him among the top physicists of all time, as it is almost certain modern physics would not have come this far without this man’s work.

Works Cited

Feynman, Richard P. (1985). QED. The Strange Theory of Light and Matter. Princeton:

Princeton University Press.

Martin, P. C., & Glashow, S. L. (2008). Julian Schwinger 1918-1994. National Academy of

Sciences. Retrieved from http://www.nasonline.org/publications/biographical-memoirs/

memoir-pdfs/schwinger-julian.pdf

Mehra, J. & Milton, K. A. (2000). Climbing the Mountain: The Scientific Biography of Julian

Schwinger. Oxford: Oxford University Press.

Milton, K. A. (2008). Julian Schwinger (1918-1994). Retrieved from http://arxiv.org/pdf/

physics/0606153.pdf

Milton, K.A. (2006). Julian Schwinger: Nuclear Physics, the Radiation Laboratory,

Renormalized QED, Source Theory, and Beyond. Retrieved from http://www.nhn.ou.edu/

~milton/papers/pip.pdf

NobelPrize. (1965). Julian Schwinger - Biographical. Nobel Lectures. Retrieved from

http://www.nobelprize.org/nobel_prizes/physics/laureates/1965/schwinger-bio.html