In letters to close associates he preferred the name lnvariantentheorie. The name stresses the notion that even though observers in different states of motion will have differing sensory experiences, laws of physics retain their validity under differing states of motion. Further, these invariant laws will explain the varying observational data. The velocity of all objects is measured relative to the particular co-ordinate system with which observer is moving. Our own selected position is the basis on which our measurements are made.
All motion is relative to our own.
Thus to repeat, with the introduction of the theory of relativity, all motion must of necessity be measured relative to the particular coordinate system chosen as the base of measurement. The measurement a motion depends on the context chosen for the measurement. They do indicate, however, that the world does not necessarily correspond to the ways we have been taught to think of it as being, nor does it necessarily correspond to our sense impressions. The theory, based on the equivalence of gravitational and inertial fields, was given its first substantiation by Sir Arthur Eddington's expedition in 1919 that during the eclipse of the sun of that year found, as Einstein had predicted, that stars which if measured rectilinearly, were behind the sun, could be seen because the sun's gravity acted as a lens and refracted the light rays from the stars around it. Hence, all straight lines are curved according to the gravity of the bodies of space and the bodies themselves are rushing outward from one another.