Here's why:
* The speed of light is a constant: The speed of light in a vacuum is a fundamental constant of the universe. It doesn't change, regardless of the observer's motion.
* Light slows down in matter: When light travels through a medium like air, water, or glass, it interacts with the atoms and molecules in the medium. This interaction causes the light to slow down.
Therefore, light can't travel faster than it does in a vacuum, but it can travel *slower* in different materials.
What you might be thinking about:
You might be thinking of the concept of the refractive index. This is a measure of how much light slows down when it enters a material. Materials with a higher refractive index cause light to slow down more. For example, glass has a higher refractive index than air, so light travels slower in glass.
Let me know if you have any other questions!
