Daniel_

Right.

Thought experiment. You are in a vacuum. You are hanging in an empty part of space.

Designate the long axis of your body as UP. Designate the direction you are facing as NORTH.

Shine a YELLOW laser EAST, and another WEST.

From your POV, there are two yellow photons going away from you at C

Therefore from your perspective, the photons relative speed seems to be 2C.

If you were sitting on the yellow photon, looking back past the person shining the light what would you see?

You would see not a yellow photon going away at 2C, you would see a RED photon going away at 1C.

Look up Redshift, and it will help explain.

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Overhead, the Albatross hangs motionless upon the air,
And deep beneath the rolling waves,
In labyrinths of Coral Caves,
The Echo of a distant time
Comes willowing across the sand;
And everthing is Green and Submarine
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