Shouldn't the index of refraction change?

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SUMMARY

The index of refraction remains constant despite random Brownian motion due to its nature as a macroscopic material property. The discussion clarifies that while light interacts with particles within a medium, the microscopic randomness averages out, resulting in a stable index. The explanation provided in popular videos oversimplifies the physics, failing to account for the consistent behavior of light direction within materials. This distinction is crucial for understanding the fundamental principles of optics.

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  • Understanding of the index of refraction in optics
  • Basic knowledge of Brownian motion and its implications
  • Familiarity with macroscopic versus microscopic properties
  • Concept of light propagation and particle interaction
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Physicists, optics researchers, and students studying light behavior in various materials will benefit from this discussion.

mero55
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Shouldn't the index of refraction change due to the random Brownian motion.
I watched a video recently that explained why light slowed down in different mediums and said that it was due to the fact that the light ray has to bounce off several particles before it leaves the medium its in.(Note that the light ray hits the particles at the speed of light)
But how can we have a constant index of refraction if we don't know how many particles the ray has to hit before it leaves the medium?!
 
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Change relative to what?
Index of refraction is a macroscopic material property, everything random that happens at the microscopic level averages out.
mero55 said:
I watched a video recently that explained why light slowed down in different mediums and said that it was due to the fact that the light ray has to bounce off several particles before it leaves the medium its in.(Note that the light ray hits the particles at the speed of light)
That is just an attempt to explain the concept to non-physicists - it is not the actual physics, it is a model and it has many limitations. As an example, it cannot explain why light does not change its direction randomly in a material.
 

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