Light moves at 299,792,458 meters per second in a vacuum, but it slows down in different materials. In water, it’s about 25% slower. In diamond, it crawls at less than half its usual speed. Scientists have even found ways to slow light down to a near stop using supercooled atoms. But here’s the wild part—when light exits these materials, it instantly resumes its full speed. It never “accelerates” back up. That’s just how light works.