Light travels at speed x through a vacuum, and then it encounters a physical medium and slows down, only to leave the physical medium and re-enter vacuum. The speed of light immediately re-accelerates to speed x, the speed before going through the physical medium. How does this happen, what is the cause of this?
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When light travels through a physical medium the photons don't actually slow down. They still travel at the speed of light. What makes it look like it slows down is the interactions between the photons and the physical medium. For example the electrons in atoms can absorb photons and go to a higher energy state and then re-emit the photons when they move back to their normal energy state. How long it takes between the absorption and emission of the photons determines how fast the light moves through a medium. |
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You should remember that photons have no rest mass so an (essentially) instantaneous change in velocity is possible. There are however near field edge affects at the boundaries which probably should be accounted for so it isn't quite as simple as that.. |
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protected by ACuriousMind♦ 1 hour ago
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