What We Cannot Know: Explorations at the Edge of Knowledge

by Marcus du Sautoy

Even stranger particles that had not been predicted at all were soon leaving trails in Anderson’s cloud chamber. Anderson started to analyse these new paths with his PhD student Seth Neddermeyer in 1936. The new particles corresponded to negatively charged particles passing through the cloud chamber. But they weren’t electrons. The paths these new particles were leaving indicated a mass much larger than that of the electron. Just as Thomson had done, mass can be measured by how much the particle is deflected under the influence of a magnetic field. The particle seemed to have the same charge as the electron but was much harder to deflect. Now called the muon, it was one of the first new particles to be discovered in the interactions of cosmic rays with the atmosphere.