Till now I have learned that light has fastest speed. But I have also noticed that wherever it travels it only experiences retardation. So I wanted to know if light ever felt acceleration naturally in universe.
Additional possibility: when light travels through a medium such as water, it slows down substantially. If light leaves water and enters air, it does in fact speed up when it enters the air. I have no idea how to calculate the time required for this "speed up" to happen, but if the time interval can be calculated or measured, you can calculate an acceleration for this circumstance.