Time is Not Universal

         The relativity of simultaneity is the difference in the way two observers can witness an event. For instance, an observer in the middle of a stationary platform can have a light source emitted at both ends and conclude that the light sources reach him at the same time. These events occurred simultaneously. However, if an observer is to move relative to this platform, one light source will appear to start traveling at a later time than the other. Consequently, the events are not simultaneous to the moving observer.

        The concept of the relativity of simultaneity can often be confused with what John Norton refers to as "appearance simultaneity." This is when two events appear to be or not be simultaneous based on our sensation of them. An easy example to distinguish between the two concepts is with a lightning strike. For an observer far away, the light will arrive first, and then the thunder sound later. These events are not showing the relativity of simultaneity, rather the difference in the speed of sound and light. After all, we can conclude that the thunder and lightning were the same event of a lightning strike. The difference comes from our senses of the event, causing us to think the events did not occur at the same time.

        Time as a universal concept is unreal in special relativity. Clocks, for instance, will appear to tick slower when moved in relation to a stationary one. Traditionally, people would have thought that the time is the same regardless of where one is in the universe. Relative motion would not seem to have a meaningful impact on time. However, special relativity shows that time will actually change with relative motion. So, time is subjective to the observer, not universal.