Einstein’s theory of relativity is founded on the **speed of light being constant**. However, there are postings and scientific discussions where there is mention of “**light slowing down traveling through materials”**. Does it really slow down in the material or is the entrance/exit delay explained by something else?
For example, would it instead be explained that the photons are absorbed and then re-generated on the other side of atoms as they make their way through water, glass, etc? The “delay” is then actually a measure of the time spent between absorption and emission?
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The light does actually go slower through a medium.
The wave version of this is that the EM field of the light interacts with the charged elements of the atoms in the vicinity that it is traveling through. These charges are disturbed and generate their own EM waves with the same frequency at which they were excited (the light’s frequency), but with a different phase. These waves when summed with the incident light wave (superposition) result in a wave that is going slower than the light in a vacuum.
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