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 Hendrik Antoon Lorentz. Required to describe phenomena approaching the speed of 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