光が真空以外の培地に入ると、遅くなります。光が培地を出て、真空に戻ると、速度が上がります。光を加速するエネルギーはどこにありますか？
When light enters a medium other than a vacuum it slows down. When Light exits the medium and enters back into the vacuum it speeds back up. Where does the energy come that accelerates the light?