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If you can slow down the speed of a photon, how does it speed back up to the speed of light once the slowing down is disabled?

Qmechanic
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Sean
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2 Answers2

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You can't slow down a single photon, you can only slow down the average speed of a group of photons with things like absorption and reemission in a medium.

Señor O
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Technically, a single photon always travels with the speed of light in the vacuum, it cannot be slowed down or accelerated. The light wave travels in a medium slower because it is composed of many photons that interact with the medium, being absorbed and reemitted, and that slows the whole wave down. But once the wave leaves the medium back into the vacuum, once again photons travel freely.

Adam Latosiński
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