>>But it only has so much energy it can give, and once it hits certain thresholds, begins to deliver less energy, not to mention move slower.
>
>What do you mean with "give"? As long as a photon travels through empty space, and isn't absorbed, it should not lose any energy.
>
>>Light moving slowly when we're not expecting it gives the optical illusion of there being extra space for it to travel through.
>
>As far as I know, there is no indication whatsoever that light can move at any speed different from the "speed of light".


Hubble redshift is such an indication.

Scientists don't want to admit that it slows down, so they invent extra space (expansion) to account for the observations.

But it's just a mathematical trick, an illusion that results from a belief that light travels infinitely far without ever changing.