The possibility has been recently demonstrated to manufacture
(nonrelativistic, Hamiltonian) many-body problems which feature an isochronous
time evolution with an arbitrarily assigned period T yet mimic with good
approximation, or even exactly, any given many-body problem (within a quite
large class, encompassing most of nonrelativistic physics) over times
T~ which may also be arbitrarily large (but of course such that
T~<T). In this paper we review and further explore the possibility to
extend this finding to a general relativity context, so that it becomes
relevant for cosmology.Comment: Submitted to Acta Appl. Mat