Friday, 11 February 2011
How is Spontaneous Symmetry Breaking Possible?
David John Baker
University of Michigan, Department of Philosophy
12:05 pm, 817R Cathedral of Learning

Abstract:We pose and resolve a seeming paradox about spontaneous symmetry breaking in the quantum theory of infinite systems.  For a symmetry to be spontaneously broken, it must not be implementable by a unitary operator.  But Wigner's theorem guarantees the existence of a unitary operator that preserves transition probabilities for pure states.  We show how it is possible for a unitary operator of this sort to connect the folia of unitarily inequivalent representations.