1) An event is a physical happening that occurs at a specific place and time, as recorded by observers using reference frames consisting of coordinate systems and clocks at rest relative to the frames. 2) Special relativity has two postulates: 1) the laws of physics are the same in all inertial reference frames, and 2) the speed of light has the same value in all inertial frames regardless of the motion of the light source or observer. 3) Time dilation occurs such that clocks in motion run slower than clocks at rest, as observed from another frame, with the time interval between ticks increasing with the relative velocity between frames. Proper time is the time interval measured in the frame at rest with the clock