The following comments by Lawrence Krauss appear in the booklet that accompanies the 1986 Dirac Memorial Lecture by Richard Feynman titled The Reason for Antiparticles. The video was available from the Tuva Trader.
Richard Feynman begins this Dirac Lecture by paying homage to Dirac, so let me begin this preface by repaying him in kind. For most physicists of my generation, Feynman stands head and shoulders above anyone in the second half of the twentieth century as a physics “hero”. Many of us first learned of him through his Feynman Lectures on Physics, a trilogy of introductory physics texts (which many of us have since referred to in our own research work, demonstrating that they really weren’t that introductory after all), or through his popular book, The Character of Physical Law, the written version of his famous Messenger Lectures at Cornell. I remember picking up this book when I was in high school, when a teacher suggested I read the section on antiparticles and going backward in time. Like many a young physicist before and since, from the minute I picked up this book, I was hooked. The idea that the existence of antiparticles in nature had something to do with time reversal symmetry was intoxicating. Feynman returned to this theme in his Dirac Lecture. Given that my own introduction to Feynman had to do with antiparticles, it is thus a particular pleasure and privilege to be able to write this short introduction to Feynman’s Dirac Lecture on the same subject.
What made Feynman so unique was not simply the breadth and depth of his own work, which was considerable indeed he changed the way we think about the world of elementary particle interactions, and made fundamental contributions to a variety of other areas of physics including gravitational theory and condensed matter physics. Rather what distinguished Feynman was the originality with which he approached all aspects of physics. It seems clear that in the process of learning physics he independently re-derived from scratch nearly every result that he talks about. As a consequence, his discussions about topics as simple as Newton’s Law of Gravity, and as complex as the relationship between spin and statistics in quantum field theory are both fresh and new.
What is also clear is that Feynman, in spite of his considerable wit and showmanship, was always dead serious about physics. Late in his life he clearly got used to huge crowds whenever he talked, on whatever subject he talked about. This clearly frustrated him. While he seemed to enjoy the celebrity at some level, it is also obvious that he also felt that if he wanted to talk about physics at a technical level, people who merely wanted to watch shouldn’t expect anything but physics. I remember once hearing him address a joint Harvard/MIT physics seminar with a large room full of people, and he began by saying that most people in the room should probably leave, and then he immediately began to lecture on Quantum Chromodynamics, the theory of the strong interactions between quarks. What he may not have appreciated was that the Boston theoretical physics community was large enough to fill the room with experts! Viewers of this tape of the Dirac Lecture may be surprised by how quickly Feynman jumps into his subject here. I think that his concern that when he was talking about physics, people should be prepared to listen to physics, goes a long way toward explaining this.
Feynman’s topic in this Dirac lecture is a classic subject in the field one which is at the heart of every course in quantum field theory, and in which it would be difficult, as a physicist, to expect to glean new insights. Of course this expectation is incorrect. I remember how reading the text of his Dirac Lecture, I was amazed at how it was possible physically to understand the connection between the sign associated with particle exchange in interfering Feynman diagrams in calculating physical amplitudes and the phenomena of Bose condensation. Immediately after reading this work I began to think about how this might be applied to particles called anyons, which in two-dimensional theories can have statistics involving arbitrary phases. Since some people had discussed such particles as being possibly related to the existence of high temperature superconductivity, it seemed worthwhile thinking about their condensation properties. The insights I gained from Feynman’s lecture led me to discuss this with a colleague of mine, who was an expert in condensed matter physics and who immediately recognized the significance of this notion in the context of work he was already doing on anyon condensation.
I have never read anything by Richard Feynman which did not cause me to gain new insights into the universe. I know of no higher complement I can give him. Of course, merely reading Feynman is to miss half the fun. His warmth, the ever-present sparkle in his eyes, the jokes and stories, the accent, all contributed to the special feeling his colleagues had for him. But above it all, he was always able to get right to the heart of the physics in a unique, clear and direct mathematical style. It is a real treat to have the opportunity, years after he passed away, to watch him “perform” again. We shall miss him, and the world is poorer for his absence.
Lawrence M. Krauss
Ambrose Swasey Professor of Physics,
Professor of Astronomy, and
Chairman, Physics Department,
Case Western Reserve University