Depends on the fiber. All fiber is not created equal.What speed does the light travel in that controlled circumstances?
I wasn't talking about trillions of miles of space... or measuring the cosmos. Just one tiny part of it.As you noted, there are temperature and other effects on even that controlled circuitry, which is powered to a level high enough to overcome most of the environment. Trillions of miles of space has lots of interference. I'm just saying they don't have enough info or sufficient testing to create an absolute speed of light, and then use that figure to measure the cosmos, then present that as absolutes.
I was talking about a few miles of optical fiber.
Yeah!We had testboard men in the old days that could pit you within feet of a bad copper splice with Wheatstone bridges, cable maps, and ambient air temp.
Think of what they could do today.
It's getting done... everyday.