They all travel through a vacuum at the speed of light .
All electromagnetic waves travel at the speed of light in a vacuum but they travel at slower speeds when they travel through a medium that is not a vacuum .
All electromagnetic waves travel at the speed of light in a vacuum but they travel at slower speeds when they travel through a medium that is not a vacuum .
간단한 표현으로 다시 작성: They all travel through a vacuum at the speed of light . 산출: