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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Light really does slow down.
Edit: there’s lots of ways that you can speculate. But the classical physics answer is that Light is an “electromagnetic wave” when this interacts with the electromagnetic field created by the electrons in the glass, it causes the wave to slow down.
There are many reasons the absorption-emission theory (or the bouncing light theory) cannot work.
First, it would be far too slow. While absorption of light is quick, you then have to wait for emission. Second, emission happens in all directions, so light entering would be turned into a ball of light, this would be similar to the reason the bouncing theory cannot work as it would just send light flying in all different directions. Third, atoms are too far apart. Fourth, there would be a point where the absorption of the material is saturated. So would light pass through at the speed of light? Fifth, emission spectra (color) is not dependent on the absorption color so the light you get out could be green even if the input light was blue. You also cannot usually get out a shorter wavelength of light from emission. There’s probably some more reasons but that’s all I can think of now.
What is constant is the speed of light in vacuum, according to the theory of relativity. Not the speed of light in general
Light really does slow down.
Edit: there’s lots of ways that you can speculate. But the classical physics answer is that Light is an “electromagnetic wave” when this interacts with the electromagnetic field created by the electrons in the glass, it causes the wave to slow down.
There are many reasons the absorption-emission theory (or the bouncing light theory) cannot work.
First, it would be far too slow. While absorption of light is quick, you then have to wait for emission. Second, emission happens in all directions, so light entering would be turned into a ball of light, this would be similar to the reason the bouncing theory cannot work as it would just send light flying in all different directions. Third, atoms are too far apart. Fourth, there would be a point where the absorption of the material is saturated. So would light pass through at the speed of light? Fifth, emission spectra (color) is not dependent on the absorption color so the light you get out could be green even if the input light was blue. You also cannot usually get out a shorter wavelength of light from emission. There’s probably some more reasons but that’s all I can think of now.
What is constant is the speed of light in vacuum, according to the theory of relativity. Not the speed of light in general
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Light really does slow down.
Edit: there’s lots of ways that you can speculate. But the classical physics answer is that Light is an “electromagnetic wave” when this interacts with the electromagnetic field created by the electrons in the glass, it causes the wave to slow down.
There are many reasons the absorption-emission theory (or the bouncing light theory) cannot work.
First, it would be far too slow. While absorption of light is quick, you then have to wait for emission. Second, emission happens in all directions, so light entering would be turned into a ball of light, this would be similar to the reason the bouncing theory cannot work as it would just send light flying in all different directions. Third, atoms are too far apart. Fourth, there would be a point where the absorption of the material is saturated. So would light pass through at the speed of light? Fifth, emission spectra (color) is not dependent on the absorption color so the light you get out could be green even if the input light was blue. You also cannot usually get out a shorter wavelength of light from emission. There’s probably some more reasons but that’s all I can think of now.
What is constant is the speed of light in vacuum, according to the theory of relativity. Not the speed of light in general
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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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