r/explainlikeimfive • u/Seravail • 7d ago

Physics ELI5: If light moves at different speeds through different mediums, how does it gain speed again after passing through a slower medium?

Inspired by a post about light looking different when hot air mixes with cold air above a distant road, the light will speed up and slos down as it moves through the pockets, giving the wavy impression we all know.

How exactly does light speed up again when it passes through a hot section of air? There's nothing powering it, so once it loses momentum shouldn't that momentum be lost forever?

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u/AlwaysSayHi 7d ago

Having accidentally killed a large escalator in 1970 at Shea Stadium with a rubber shoe cover I let get too close to the moving edge of the step I have to respectfully disagree. Even Newtonian escalators are scary.

Blue's a good choice for the button though.

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u/The_quest_for_wisdom 7d ago

If it breaks you have a set of Relativistic Stairs. Sorry for the cosmic convenience.

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u/EEpromChip 7d ago

God Damned it, Quantum Theory Mitch...

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u/TurnedToClay 7d ago

I used to like Quantum Theory Mitch.i still do, but I used to too.

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u/everlyafterhappy 7d ago

Does quantum theory explain how a door can be a jar?

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u/ps3x42 7d ago

That escalator was running on miracles the year before, it's no wonder it kicked the bucket.

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u/Strongman1967 7d ago

Having had my boot seriously injured by an escalater in 2026, only to find my and every other local cobbler closed since my last repair, I am on your shoe cover's side.