Set of equations in relativity physics that relate the space and time coordinates of two systems moving at a constant speed relative to each other, developed in 1904 by
Required to describe phenomena approaching the speed of {{link=light">light , these transformations express the concepts that space and time are not absolute; that length, time, and mass depend on the observer's relative motion; and that the speed of light in a vacuum is constant and independent of the motion of the observer or the source.