One postulate of special relativity theory is that the laws of physics are the same in all inertial frames of reference The other postulate is that the speed of light in a vacuum is the same in all inertial frames

Einstein showed that simultaneity, or lack of it, depends on the frame of reference of the observer Time dilates, length contracts, and momentum increases as an object approaches the speed of light

special relativity — the theory proposed to explain the consequences of requiring the speed of light and the laws of physics to be the same in all inertial frames. relativity — the explanation of how objects move relative to one another. postulate — a statement that is assumed to be true for the purposes of reasoning in a scientific or mathematic argument. frame of reference — the point or collection of points arbitrarily chosen, which motion is measured in relation to.