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This question seems a lot like one of those "Phylosoraptor" memes all over the Internet, and it might be very silly, but I've been thinking about this for a while.
Is it possible that space is not actually expanding but rather, the speed of light is decreasing throughout the entire Universe? ...as if light were traveling through a medium that would be changing its properties over time.
I guess there are several phenomenons that can be explained just as well by assuming that either space is expanding, either light is slowing down, but I do not know enough physics (and phenomenons that could contradict such a claim) in order to rule out this possibility.