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Why is light slower in glass? - Sixty Symbols

Sixty Symbols · 847.9K views · 2013-07-11 · 16:30

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Overview

Professor Mike Merrifield of Nottingham explains in a mostly uncut conversation why light travels slower in glass. He treats light as a wave and describes how the material's electrons produce secondary waves that combine to slow it.

On Hacker News

HN cites it whenever the popular absorb-and-re-emit explanation comes up, as a source for the wave-interference account.

Recommended by 1 HN people across 1 months · HN mentions 2018–2021

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Fundamental physicsEveryday physics & science demos
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refractionspeed of lightopticswave physicsphase velocity

What people said

7373737373 · 2019-12 · Recommendation

This reminds me of this Sixty Symbols video which explains why light is slower in media such as glass than in a vacuum: [VIDEO] The incoming light wave causes an avalanche of secondary waves through electromagnetically perturbing the individual atoms, and the superposition of all these results in a wave that seems to travel slower than the speed of light.

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wruza · 2021-09 · Reference

Both ideas are incorrect. Bouncing around would be random and the outgoing light would be scattered (as in matte reflections) in all directions. Absorbtion simply destroys the original light. If photons are mostly absorbed, we call that “a wall” or ”a fog”, not “a transparent medium”, which to be transparent shouldn’t have electrons whose energy level differences correspond to a photon’s wave length. The transparency and slowdown effect is a complex interaction between fields in the medium, which I honestly don’t have enough courage to retell. [VIDEO]

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vecter · 2020-12 · Reference

> Well, actually, the speed of light is constant, it just takes time to ping-pong around a lattice/gas. Photons hit particles, get absorbed, and re-emitted, which causes an effective slowdown at a larger scale. A gas is just vacuum with particles floating around in it. When photons travel between those particles, they are traveling at c. The effective slowdown is determined by the lattice/gas, and we denote this slowdown with the refractive index... This is wrong. Two sources [0][1]. [0] [LINK] [1] [VIDEO]

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Sources

Video by Sixty Symbols, played through YouTube.

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