GENERAL ARTICLE Hiding in the Mirror Lawrence M Krauss That was a moment when I knew how nature worked. —RICHARD FEYNMAN The same mesons that had begun to invade Richard Feynman’s world in 1950 had turned every particle physicists’ world upside down by 1956. New particles kept being discovered, and each one Lawrence M Krauss is an was stranger than the one before. Particles were produced strongly internationally known theoretical physicist. His in cosmic rays, but the same physics that produced them should studies include the early have caused them to quickly decay. Instead, they lasted as long as universe, the nature of a millionth of a second, which doesn’t sound too long, but is dark matter, general millions of times longer than one would predict on the basis of relativity and neutrino astrophysics. Prof. Krauss first principles. is the Foundation Professor in the School of By 1956, Feynman’s fame among physicists was secure. Feynman Earth and Space Explora- diagrams had become a part of the standard toolbox of the physics tion and Physics Depart- community, and anyone who was passing through Caltech would ment, and Inaugural make every effort to pay homage. Everyone wanted to talk to Director of the ‘Origins Project’ at Arizona State Feynman because they wanted to talk about their own physics University. ‘Origins’ will problems. The very same characteristic that made him so irresist- become a national center ible to women worked wonders on scientists as well. It was a for research and outreach characteristic he shared with the remarkable Italian physicist on origins issues, from the origins of the universe, to Enrico Fermi, the Nobel laureate who helped lead the Manhattan human origins, to the Project to build the first controlled nuclear reactor at the Univer- origins of consciousness sity of Chicago, and the last nuclear or particle physicist who was and culture. equally adept at theory as at experimentation. Fermi had won the Nobel Prize for developing a simple theory that described the This article is taken from the latest biography on Feynman. It is reprinted from ‘QUANTUM MAN: Richard Feynman’s Life in Science’ by Lawrence Krauss. [Copyright (c) 2011 by Lawrence Krauss. Used with permission of the publisher, W. W. Norton & Company, Inc.]. Prof. Krauss writes about Feynman’s collaboration with another famous particle physicist, Murray Gell-Mann, in explicating the mathematics of the weak interaction and parity violation and Feynman’s acknowledgment that E C G Sudarshan should have been properly credited for having proposed the same before them. RESONANCE September 2011 801 GENERAL ARTICLE Since the neutron lived nuclear process associated with the decay of the neutron into a almost ten minutes proton (and an electron and ultimately a new particle that Fermi before decaying, a had dubbed a neutrino—Italian for “little neutron”), so-called virtual eternity beta decay, one of the essential processes that formed a part of the compared to the reactions that led to both the atomic bomb and, later, thermo- lifetimesof the nuclear weapons. unstable strongly interacting mesons Since the neutron lived almost ten minutes before decaying, a that were being virtual eternity compared to the lifetimes of the unstable strongly discovered in the interacting mesons that were being discovered in the 1950s, it was 1950’s, it was recognized that the forces at work governing its decay must be recognized that the very weak. The interaction that Fermi developed a model for in forces at work beta decay was therefore called the weak interaction. By the mid- governing its decay 1950s it had become clear that the weak interaction was a wholly must be very weak. distinct force in nature, separate from the strong interactions that were producing all of the new particles being observed in accel- erators, and that this force was likely to be responsible for the decays of all of the particles with anomalously long lifetimes. But while Fermi’s model for beta decay was simple, there was no underlying theory that connected all of the interactions that were being observed and ascribed to this new force. Fermi had built the University of Chicago theory group into an international powerhouse. Everyone wanted to be there, to share not just in the excitement of the physics but also in the excitement of working with Fermi. He had a highly unusual characteristic— the one he and Feynman share: When they listened, they actually listened! They focused all of their attention on what was being talked about, and tried to understand the ideas being expressed, and if possible, tried to help improve upon them. Unfortunately, Fermi died in 1954 of cancer, probably induced by Keywords careless handling of radioactive materials at a time when the Mesons, weak interactions, beta dangers involved were not understood. His death was a blow both decay, symmetries, kaons, to physics and to Chicago, where he had helped train young pions, neutrinos, parity viola- tion, V-A form, Gell-Mann, theorists and experimentalists who would come to dominate the Noether, Yang, Lee, Marshak, entire field for the next generation. Sudarshan, Feynman. 802 RESONANCE September 2011 GENERAL ARTICLE After Fermi’s death, young theorists began to be drawn to Feynman’s After Fermi’s death, magnetism. Unlike Fermi, he did not have the character or patience young theorists to diligently help train scientists. Yet, there was nothing so flatter- began to be drawn ing as having Feynman direct all of his attention at their ideas. For to Feynman’s once Feynman latched on to a problem, he would not rest until he magnetism. had either solved it or decided it was unsolvable. Many young One man who was physicists would mistake his interest in their problems for an attracted from interest in them. The result was seductive in the extreme. Chicago to Feynman’s light was One man who was attracted from Chicago to Feynman’s light was a twenty-five-year a twenty-five-year-old wunderkind named Murray Gell-Mann. If old wunderkind Feynman dominated particle physics in the immediate postwar era, named Murray Gell- Gell-Mann would do so in the decade that followed. As Feynman Mann. He had no would later describe, in one of his characteristic displays of praise patience with those for the work of others, “Our knowledge of fundamental physics who couched their contains not one fruitful idea that does not carry the name of often-marginal Murray Gell-Mann.” efforts in fancy formalism. There is little hyperbole here. Gell-Mann’s talents provided a perfect match to the problems of the time, and he left an indelible mark on the field, not just through exotic language like strangeness and quarks, but through his ideas, which, like Feynman’s, continue to color discussions at the forefront of physics today. Gell-Mann was nevertheless in many ways the oppositeof Feynman. Like Julian Schwinger, he was a child prodigy. Graduating from high school at the age of fifteen, he received his best offer from Yale, which disappointed him, but he went anyway. At nineteen he graduated and moved to MIT, where he received his PhD at the age of twenty-one. He once told me that he could have graduated in a single year if he hadn’t wasted time trying to perfect the subject of his thesis. Gell-Mann not only had mastered physics by the age of twenty- one, he had mastered everything. Most notable was his fascination with languages, their etymology, pronunciation, and relationships. It is hard to find anyone who knows Murray who hasn’t listened to him correct the pronunciation of their own name! RESONANCE September 2011 803 GENERAL ARTICLE But Gell-Mann bore a distinct difference from Schwinger that led to his attraction to Feynman. He had no patience with those who couched their often-marginal efforts in fancy formalism. Gell- Mann could see right through the ruse, and there were few physicists who could be so dismissive of the work of others as he could be. But Gell-Mann knew from Feynman’s work, and from listening to him talk, that when he was doing physics, there was no bullshit, no pretense, nothing but the physics. Moreover, Feynman’s solutions actually mattered. As he put it, “What I always liked about Richard’s style was the lack of pomposity in his presentation. I was tired of theorists who dressed up their work in fancy mathematical language or invented pretentious frame- works for their sometimes rather modest contributions. Richard’s ideas, often powerful, ingenious, and original, were presented in a straightforward manner that I found refreshing”. There was another facet of Feynman’s character, the showman, that appealed to Gell-Mann much less. As he later described it, he “spent a great deal of time and energy generating anecdotes about himself.” But while this feature would later grate on Gell-Mann’s nerves, following Fermi’s death in 1954, as he considered where he might want to work if he left Chicago, and with whom he might want to work, the choice seemed clear. Gell-Mann, along with the theoretical physicist Francis Low, had done a remarkable early calculation in 1954 using Feynman’s QED that sought to address the question of what precisely would happen to the theory as one explored smaller and smaller scales – exactly the traditionally unobservable regime where Feynman’s prescription for removing infinities involved artificially altering the theory. The result was surprising, and while technical and difficult to follow at the time, it eventually laid the basis for many of the developments in particle physics in the 1970s. They found that due to the effects of virtual particle-anti-particle pairs that had to be incorporated when considering quantum mechanical effects in QED, physically measurable quantities like the electric charge on an electron depend on the scale at which 804 RESONANCE September 2011 GENERAL ARTICLE they are measured.