The length of an object measured by a person moving along the object is the length measured by a person at rest with respect to the object. The speed of light measured by a person moving at a constant speed close to the speed of light is the speed measured by a person at rest. According to a person at rest, the period of a moving clock is the period of an identical clock at rest. If a star is 50,000 light years away, we see it today as it was 50,000 years ago. If we travel at the speed of light for 1 year (as measured by us), when we return to Earth we are 1 year older. Special relativity says that all observers must measure the same time between events. Soumettre Rponse Tries 0/99