Isomorphism Problem Revisited: Information Spectrum Approach

Abstract: The isomorphism problem in the ergodic theory is revisited from the perspective of information spectrum approach, an approach that has been developed to investigate coding problems for non-ergodic random processes in information theory. It is proved that the information spectrum is invariant under isomorphisms. This result together with an analysis of information spectrum provide a conceptually simple proof of the result by \v{S}ujan, which claims that the entropy spectrum is invariant under isomorphisms. It is also discussed under what circumstances the same information spectrum implies the existence of an isomorphism.