Is dark energy evenly spaced throughout Universe? Are there certain parts of the Universe that are expanding faster than others? Is there anyway to definitively measure this?
If dark energy varied by location, then plots of 1a supernova brightness vs redshift should vary depending on which direction you look in the sky. AFAIK, that's not the case. For example, although coords are not accounted for, there's not a lot of scatter in this plot:




  In the relationship between the distance and redshift of Type 1a supernovae, the data (points) agree with the equation in which light propagates through the expanding universe on the least-time path (solid line). Image credit: Annila. ©2011 Royal Astronomical Society


Read more at: http://phys.org/news/2011-10-supernovae-universe-expansion-understood-dark.html#jCp