When Murray Gell-Mann was starting out in physics, one of the big mysteries in the field was to understand the strong interactions, and especially the hadron resonances that proliferated in the 1950's. The existence of these resonances showed clearly that something very new was happening in physics at an energy scale of order one GeV. Another important mystery was to find the correct description of the weak interactions, and among other things to overcome the problems associated with the unrenormalizability of the simple though relatively successful Fermi theory. This problem pointed to a new development at a significantly higher energy scale.

Murray Gell-Mann played a tremendous role in advancing the understanding of these mysteries. His great contributions include his work on the strange particles; the “renormalization group” introduced by Gell-Mann and Low; early ideas about intermediate weak bosons; contributions to the proper description of the structure of the weak current; the unearthing of the SU(3) symmetry of strong interactions, and his contributions to the understanding of current algebra; the introduction of the quark model, and early ideas about QCD. His insights on these and other scientific problems are part of the foundation on which we now attempt to build, and his enthusiasm for science is an inspiration to all of us.

If we ask today what are some of the key new mysteries in particle physics, there are at least three that seem particularly pressing.