Special relativity says that all observers moving at constant speed will measure the same value of the speed of light.

Question

Quizplus · Accepted Answer

This is one of the fundamental principles of special relativity, known as the constancy of the speed of light. No matter how fast an observer is moving, they will always measure the speed of light to be the same value, approximately 299,792,458 meters per second.

Special Relativity Says That All Observers Moving at Constant Speed