Yoichiro Nambu and the Concept of Apparent Vacuum: A Stepping Stone to Spontaneous Symmetry Breaking

The processes of discovery and concept formation are as mysterious as they are intriguing. In this article, they give a sketch of Yoichiro Nambu’s long path toward the concept of spontaneous symmetry breaking focusing on the pivotal role played by his notion of “apparent vacuum”. This is instrumental to draw the original analogical correspondence between the vacuum of quantum field theory and solid matter, which, transforming over time in its use and purpose, enables Nambu to arrive at the concept of spontaneous symmetry breaking. From this historical episode they draw a methodological lesson and emphasise the broad cultural influences that conditioned the conceptual development.