Abstract

This essay expounds the algebraic framework describing general physical theories, within which the phenomenon of spontaneous symmetry breaking makes its appearance in infinite quantum systems. This is in contrast with the fact that a large class of theories - both classical and quantum, finite and infinite - are termed, in the conventional account of classical and quantum mechanics, as exhibiting SSB. This discrepancy will be understood in the light of an interpretation that finds the symmetry breaking to be in some respects stronger in the algebraic account than is generally the case in the conventional picture. The case of SSB in the standard account of quantum field theory will then be discussed, and it will be argued that, although one would expect a connection with the algebraic account to be possible, this turns out to be problematic. Finally the role of the idealisation of infinite systems, crucial to algebraic SSB, will be discussed.