Title text:
Imagine you could ride alongside a sound wave. It would probably be pretty cool, right? We're putting in a departmental budget request to buy a really fast plane so we can check it out.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3238/
Speed of light in fiber is ~0.66c₀. Light is slowed down a bit by air, too. So...
That is not the speed of light through fiber. That is the speed of light bouncing at diagonal angles as it travels through fiber.
It appears to travel slower because it's not traveling in a straight line. But I promise, every individual photon is traveling at exactly c. Photons emmited simultaneously will not all arrive at a destination at the same time, but this isn't because they're traveling at different speeds, it's because they're taking different paths, reflecting and refracting slightly differently.
I thought the majority of the slowdown was because of the refractive index of the glass, where the wave does actually travel slower through the fiber even if it was going in a completely straight line.
Individual photons still travel at exactly c, but there is an effect which I don't understand that causes the light to slow down (I was taught that this was because light was absorbed and reemitted by the glass molecules but from googling it that's not true)