* Interaction with Matter: Light waves are made of oscillating electric and magnetic fields. When these fields encounter the atoms and molecules of a material, they interact. The electrons in the atoms absorb and re-emit the light energy, which slightly delays the light's progress.
* Index of Refraction: This slowing down is quantified by the *index of refraction* of the material. Air has an index of refraction slightly greater than 1 (around 1.0003), meaning light travels about 0.03% slower in air than in a vacuum.
* Different Materials, Different Speeds: Denser materials, like glass or water, have higher indices of refraction, causing light to slow down even more significantly.
Important Note: While light slows down, its frequency remains constant. The slowing down effect is due to the decrease in the wavelength of light as it passes through the material.
