Why Newton’s absolute space-time is not so absolute and Einstein’s relative space time is not so relative

All of us are used to thinking that space and time in Newton’s theory of universal gravitation are absolute, while those in Einstein’s theory of Relativity are relative. And in a sense that is true, of course: indeed, the existence and properties of Newton’s space-time are independent of anything else, while those of Einstein’s are strictly related to the mass and the state of motion of material bodies. But this holds only locally: things prove to be extremely different, indeed, when considering the situation on the cosmological scale, where two absolute reference systems (galaxies at the cosmic scale and the cosmic microwave background) can be identified, paradoxically just as a consequence of the application of Relativity itself to cosmology. However, it will turn out that, far from being a defect, this makes Einstein’s Relativity even more coherent and harmonious, by solving some of its most puzzling problems; while, on the other hand, we will see that what made any possible reference system, and thus any possible motion, completely relative was just the exaggerated absoluteness of Newtonian space and time.