"The idea of spontaneous symmetry breaking was introduced into particle physics by Nambu ... in 1960. He suggested that the low mass and low-energy interactions of s could be understood as a reflection of a spontaneously-broken chiral symmetry, would have been exact if the up and down quarks were massless. His suggestion was that light quarks condense in the vacuum, much like the s of superconductivity. When this happens, the ‘hidden’ chiral symmetry causes the pions’ masses to vanish, and fixes their low-energy s to s, s and each other."