Since we know that it isn’t constant with time, how can we be sure that it is constant with space? This might be a reason the variability in our measurements which seem to disagree.
Put another way, why couldn’t the universe expand in one direction preferentially compared to another?
Right, but the velocity component would still be present in some form due to the gravitational attraction between bodies. I don’t know how significant this would be compared to the redshift value from the initial kick from inflation, or if it is possible to separate the two components somehow.
Gravitational attraction is not a relevant factor on the largest scales where dark energy takes over. To be more precise, it’s possible to measure the effects, and to describe a specific distance limit between two bodies where they can no longer become gravitationally bound and are doomed to eventually expand out of each others’ event horizons. That limit is the precise boundary between gravitational dominance and DE dominance.
To be specific, literally everything outside of the Virgo Supercluster (home to Andromeda and Milky Way among others) is outside of this limit, and will eventually become impossible to detect because the light between us and them isn’t moving as fast as the rate of expansion between us and them. Everything within the supercluster is gravitationally bound, and will eventually (iirc, grain of salt on this one) form a supergalaxy.
Wow. So it’s like that adage. However big you think space is, it’s much bigger than that.
It’s hard to fathom scales at which being gravitationally bound is insignificant relative to those type of effects.
Yes.