Observable consequences of dynamical compactification in Kaluza-Klein cosmology

Time variation of the compactified size of the extra small space is inevitable in Kaluza-Klein type of theories. This can generate observable remmants of ultrahigh energy cosmic rays that have an enhanced spectrum around 10¹⁹-10²⁵ eV. This and other consequences of the time variation are closely examined in a model that realizes compactification via the gravitational Casimir energy.