Relearning Refraction ft. Relativity

Special relativity states that the light speed is always fixed. This was (and is) very counter intuitive to understand, but it is what it is.

For example, if you are going at a speed of 0.8c (c = speed of light) along the direction of light, then the conventional (newtonian) physics says that the relative velocity between you and the light is 0.2c only! That light appears to go slower if you are travelling faster.

But special relativity says NO! Irrespective of our speed, we always measure the speed of light as 'c'. It's just that. Light speed never gonna change (in this universe). Also it's the maximum limit of anything that can move. Especially, if any particle has a mass (or to be more specific, rest-mass), then they can never reach speed of light.

Now, see it in the other way around. If anything is going at less than speed of light, it should have a mass (again, rest mass) right? How about when light itself is slowing down?? Yes. Refraction. Does light gain mass during refraction??

What happens in Refraction

We know that when a light enters a medium other than vacuum, the speed can change, right? And how the speed changes is a property of the medium called "Refractive index." In high school we've had a bunch of problems over this concept.

So, when the light from vacuum enters water, does it gain mas as it slows down?? Spoiler: No.

Refraction is light interacting with particles

Seems out light is not actually slowing down even though it appears to be.

Light is just being obstructed by the particles of the medium. Essentially what is happening is that light is being absorbed by the particles, and then re-emitted by the particles of the medium..

This interaction i.e., the delay because of the absorption and remission of light is actually being appeared as light slowing down. Actually between the absorption and emission, light is still traveling at c.

So yeah, again, light speed is constant. Hence no mass gained. Einstein is right.

Just that we need to adjust our understand of refraction. In refraction, light does not slow down. It appears to be slow down.

That's it for today. Thanks for reading! Happy unlearning and relearning!

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