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A comment on Scientists Capture a “Sonic Boom” of Light. Parent comment

Re:Scientists Capture a “Sonic Boom” of Light by posterboy on Tuesday January 24, 2017 @10:34AM (#13472115)
I guess that's relative, depending on which photon is referenced. The corollary is that from the photon POV, not its speed changes, but spacetime is warped, so it sees time in its own frame of reference going faster and/or distances shorter than we.

You are both correct, but on different levels.

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Re:Scientists Capture a “Sonic Boom” of Light by lippel82 on Tuesday January 24, 2017 @11:45AM (#13472949)
>> not its speed changes, but spacetime is warped

No, in water, the spacetime is not significantly warped, certainly not warped enough to slow down light. The different speed of light in a medium compared to vacuum comes from the interaction between the photons and the medium. The photon then, effectively, becomes a hybrid "photon-medium excitation" which is an effective particle with an effective speed lower than the vacuum speed of light.

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Re:Scientists Capture a “Sonic Boom” of Light by posterboy on Wednesday January 25, 2017 @05:12AM (#13480184)
Maybe not from our point of view, but from the POV of the photon the water is moving with c_0 through the photon, so certainly relativistic effects apply.
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