A roughly accurate analogy: think of a boomerang thrown in outer space, moving at a constant velocity, but slowing its rotation over time (for some reason - work with me). The result is that over time, each loop of the boomerang will happen over a longer and longer distance.
The boomerang isn't stretched, but its spiral looping is.
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photons get stretched?
Their wave lengths get stretched.
A roughly accurate analogy: think of a boomerang thrown in outer space, moving at a constant velocity, but slowing its rotation over time (for some reason - work with me). The result is that over time, each loop of the boomerang will happen over a longer and longer distance.
The boomerang isn't stretched, but its spiral looping is.