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It's all baked into z.
z is defined based on frequency change but the frequency change must also be the amount it appears to be slowed down, since e.g. you could measure the number of peaks in a light wave coming from a galaxy as a measure of time.
For the benefit of others: in making this post Thomas is I expect motivated by my responses to his post here:
https://protokol2020.wordpress.com/2013/09/06/embarrassing-images/#comments
In an edit to my last comment, Thomas wrote:
In reply about the blue shift galaxies: they will indeed appear to be sped up from our perspective. Something moving toward us is slowed down in our reference frame by time dilation, but also appears sped up because light takes less and less time to get here. As with redshift, both of these effects are baked into z, so the final (apparent) speedup is what you get from z.
Yes. You were my inspiration for this problem.
How exactly is everything baked into z?
The mass is increased and volume is decreased by factor gamma.
So the density is increased by gamma squared.
Do we really see that?