2018 marked the 100th anniversary of the birth of Richard Feynman. As one of several events worldwide celebrating this remarkable figure in physics, a memorial conference was held at the Institute of Advanced Studies at Nanyang Technological University in Singapore from 22 to 24 October, co-chaired by Lars Brink, KK Phua and Frank Wilzcek. The format was one-hour talks with 45 minute discussions.

Pierre Ramond began the conference with anecdotes from his time as Feynman’s next-door neighbour at Caltech. He discussed Feynman the MIT undergraduate, his first paper and his work at Princeton as a graduate student. There, Feynman learnt about Dirac’s idea of summing over histories from Herbert Jehle. Jehle asked Feynman about it a few days later. He said that he had understood it and had derived the Schrödinger equation from it. Feynman’s adviser was John Wheeler. Wheeler was toying with the idea of a single electron travelling back and forth in time – were you to look at a slice of time you would observe many electrons and positrons. After his spell at Los Alamos, this led Feynman to the idea of the propagator, which considers antiparticles propagating backwards in time as well as particles propagating forwards. These ideas would soon underpin the quantum description of electromagnetism – QED – for which Feynman shared the 1965 Nobel Prize in Physics with Tomonaga and Schwinger.

**Revolutionary diagrams**

The propagator was the key to the eponymous diagrams Feynman then formulated to compute the Lamb shift and other quantities. At the Singapore conference, Lance Dixon exposed how Feynman diagrams revolutionised the calculation of scattering amplitudes. He offered as an example the calculation of the anomalous magnetic moment of the electron, which has now reached five-loop precision and includes 12,672 diagrams. Dixon also discussed the importance of Feynman’s parton picture for understanding deep-inelastic scattering, and the staggeringly complex calculations required to understand data at the LHC.

George Zweig, the most famous of Feynman’s students, and the inventor of “aces” as the fundamental constituents of matter, gave a vivid talk, recounting that it took a long time to convince a sceptical Feynman about them. He described life in the shadows of the great man as a graduate student at Caltech in the 1960s. At that time Feynman wanted to solve quantum gravity, and was giving a course on the subject of gravitation. He asked the students to suppose that Einstein had never lived: how would particle physicists discuss gravity? He quickly explained that there must be a spin-two particle mediating the force; by the second lecture he had computed the precession of the perihelion of Mercury, a juncture that other courses took months to arrive at. Zweig recounted that Feynman’s failure to invent a renormalisable theory of quantum gravity affected him for many years. Though he did not succeed, his insights continue to resound today. As Ramond earlier explained, Feynman’s contribution to a conference in Chapel Hill in 1957, his first public intervention on the subject, is now seen as the starting point for discussions on how to measure gravitational waves.

Cristiane Morais-Smith spoke on Feynman’s path integrals, comparing Hamiltonian and Lagrangian formulations, and showing their importance in perturbative QED. Michael Creutz, the son of one of Feynman’s colleagues at Princeton and Los Alamos, showed how the path integral is also necessary to be able to work on the inherently non-perturbative theory of quantum chromodynamics. Morais-Smith went on to illustrate how Feynman’s path integrals now have a plethora of applications outside particle physics, from graphene to quantum Brownian motion and dissipative quantum tunnelling. Indeed, the conference did not neglect Feynman’s famous interventions outside particle physics. Frank Wilczek recounted Feynman’s famous insight that there is plenty of room at the bottom, telling of his legendary after-dinner talk in 1959 that foreshadowed many developments in nanotechnology. Wilczek concluded that there is plenty of room left in Hilbert space, describing entanglement, quantum cryptography, quantum computation and quantum simulations. Quantum computing is the last subject that Feynman worked hard on. Artur Ekert described the famous conference at MIT in 1981 when Feynman first talked about the subject. His paper from this occasion “Simulating Physics with Computers” was the first paper on quantum computers and set the ground for the present developments.

**Biology hangout**

Feynman was also interested in biology for a long time. Curtis Callan painted a picture of Feynman “hanging out” in Max Delbruck’s laboratory at Caltech, even taking a sabbatical at the beginning of the 1960s to work there, exploring the molecular workings of heredity. In 1969 he gave the famous Hughes Aerospace lectures, offering a grand overview of biology and chemistry – but this was also the time of the parton model and somehow that interest took over.

Robbert Dijkgraaf spoke about the interplay between art and science in Feynman’s life and thinking. He pointed out how important beauty is, not only in nature, but also in mathematics, for instance whether one uses a geometric or algebraic approach. Another moving moment of this wide-ranging celebration of Feynman’s life and physics was Michelle Feynman’s words about growing up with her father. She showed him both as a family man and also as a scientist, sharing his enthusiasm for so many things in life.

- Recordings of the presentations are available online.