2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/35763We argue that space-time geometry is not absolute with respect to the frame of reference being used. The space-time metric differential form $ds$ in noninertial frames of reference (NIFR) is caused by the properties of the used frames in accordance with the Berkley - Leibnitz - Mach - Poincaré ideas about relativity of space and time . It is shown that the Sagnac effect and the existence of inertial forces in NIFR can be considered from this point of view. An experimental test is proposed.LaTex 2.09 , Lecture given at Stefan Banach Center (Warsaw), March 1996General Relativity and Quantum Cosmologytext