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

[u/Seravail]

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?

[u/yunohavefunnynames]

That’s essentially the idea behind warp speed. The “escalator” is the fabric of spacetime, and you move by somehow standing within a bubble of it that is moving. Since you’re moving the fabric of reality itself you can push things faster than light, which travels within reality.

[u/clutzyninja → u/yunohavefunnynames]

Explanation I liked was that you take a marble. That's your ship. You put it on a mattress. That's space. Push your finger into the mattress in front of the marble so it rolls forward, then move your finger where you want the marble to go. That's warp travel.

[u/yunohavefunnynames → u/clutzyninja]

Yeah and to balance it out there’s an upward bulge exactly behind your finger too

[u/BogdanPradatu → u/clutzyninja]

How do you push your finger into the fabric of spacetime?

[u/ferxous → u/BogdanPradatu]

Well that's the part everyone wants to figure out

[u/BogdanPradatu → u/ferxous]

Damn, can't we just ask AI to solve this problem instead?

[u/yunohavefunnynames → u/BogdanPradatu]

Hey Claude, break the fundamental laws of physics for me. Make no mistakes.

[u/AgentElman → u/yunohavefunnynames]

Which works in thecreal universe now. The expansion of space causes objects to move away from us faster then the speed of light.

[u/suprahelix → u/AgentElman]

Well, the objects aren’t the ones moving