This book presents interesting mathematical questions of relativity theory and relations to modern astrophysics, as well as various conceptual foundations. Topics discussed include the generalised Lorentz transformations and the velocity transformation; fundamental physics; non-Newtonian gravity effect; dark matter and dark energy concepts; pseudo-complex variables and antisymmetric tensor fields. This book will be useful for academic professors, professional researchers in physics and mathematics, postgraduate students and all remaining people interested in theoretical physics and astrophysics.