 Historically, the concept of SSB first emerged in condensed matter physics. The prototype case is the 1928 Heisenberg theory of the ferromagnet as an infinite array of spin 1/2 magnetic dipoles, with spin-spin interactions between nearest neighbours such that neighbouring dipoles tend to align. Although the theory is rotationally invariant, below the critical Curie temperature Tc the actual ground state of the ferromagnet has the spin all aligned in some particular direction (i.e. a magnetization pointing in that direction), thus not respecting the rotational symmetry. What happens is that below Tc there exists an infinitely degenerate set of ground states, in each of which the spins are all aligned in a given direction. A complete set of quantum states can be built upon each ground state. We thus have many different “possible worlds” (sets of solutions to the same equations), each one built on one of the possible orthogonal (in the infinite volume limit) ground states. To use a famous image by S. Coleman, a little man living inside one of these possible asymmetric worlds would have a hard time detecting the rotational symmetry of the laws of nature (all his experiments being under the effect of the background magnetic field). The symmetry is still there — the Hamiltonian being rotationally invariant — but “hidden” to the little man. Besides, there would be no way for the little man to detect directly that the ground state of his world is part of an infinitely degenerate multiplet. To go from one ground state of the infinite ferromagnet to another would require changing the directions of an infinite number of dipoles, an impossible task for the finite little man (Coleman, 1975, pp. 141–142). As said, in the infinite volume limit all ground states are separated by a superselection rule. Ruetsche (2006) discusses symmetry breaking and ferromagnetism from the algebraic perspective. Liu and Emch (2005) address the interpretative problems of explaining SSB in nonrelativistic quantum statistical mechanics. Fraser (2016) discusses SBB in finite systems, arguing against the indispensability of the thermodynamic limit in the characterization of SSB in statistical mechanics.