After discussing a lot in another thread, I wanted to post my POV about the metric expansion of space.
Here below a sketch of what I think is happening: in short, when the metric of space is doubled, time doesn't change.
Here we are:
Leonardo's vitruvian man on the right is double in scale relative to the left one.
If both are observers, they observe light travelling at constant velocity C, each one in their own metric.
Both are observing the same thing, there is no absolute reference that says the left man is correct while the other is wrong. Both must be correct.
So light is travelling at the same apparent velocity as observed locally by each one of them.
And the result is shown here: while space is scaled, time is not. The dot arrives at the same time in the 2 images.