Rutherford’s Legacy

It’s 100 years to the month since Ernest Rutherford published the paper that established the existence of the atomic nucleus, and in a way gave rise to much of what we do at CERN.

Rutherford’s analysis, based on measurements made by Hans Geiger and Ernest Marsden, established the existence of the atomic nucleus, and with it an understanding that what appears to be solid matter is in fact mostly empty space. As Arthur Eddington put it: “If we eliminated all the unfilled space in a man’s body and collected his protons and electrons into one mass, the man would be reduced to a speck just visible with a magnifying glass.” A sobering thought.

Nevertheless, something gives matter substance and that, of course, is the forces that act between the particles in Eddington’s tiny speck. Particle physics is the study of those particles and forces, and CERN has evolved into a world-leading centre for that study. Over the years, a common thread of CERN research has been the investigation of the electromagnetic and weak forces. It’s electromagnetism that maintains negatively charged electrons at a distance from positively charged nuclei, thereby giving rise to the atomic structure that Rutherford observed. The weak force is responsible for radioactivity, and drives the hydrogen fusion processes in stars.

Through the 1960s and 1970s, the theoretical underpinning of particle physics, the Standard Model, took shape and with it came the notion that all the forces could be unified into a single theory. In the 1970s, CERN’s Gargamelle experiment brought the first hints that this was so, producing evidence that the weak and electromagnetic forces were manifestations of the same phenomenon. The Nobel Prize-winning discovery of the mediators of the weak force, the W and Z particles, in the 1980s, confirmed this result. And through the 1990s, LEP put electroweak theory on solid experimental ground.

Today, the Standard Model is almost complete, and with the LHC we are poised to go beyond, to a new level of understanding of particles and forces. After Rutherford, things were never the same again. I wonder if, another 100 years from now, people will say the same of the LHC?

Rolf Heuer