Instantons

Instantons are solutions in quantum physics that describe rare, short-lived events where a system transitions between different states in a way that classical physics cannot explain. They illustrate how particles or fields can spontaneously change configurations due to quantum effects, often occurring in extreme conditions like the early universe or high-energy environments. Essentially, instantons represent "tunneling" phenomena—where systems bypass energy barriers—providing insights into processes such as particle interactions and phase changes in fundamental physics.