How to Measure the Expansion of Space

If there was no acceleration, no dark energy then essentially everything would be in one big inertial frame and those two pictures would be equivalent. But because there is acceleration you can't put everything into one big inertary frame. The acceleration is what means those things really are in their own separate frames. So that's sort of measurement of the expansion of space and its acceleration is not like a real measurement that you could make. It's not something you could actually measure. Whereas thinking about it from the other point of view and just thinking about how distant galaxies are moving away from us and measuring their velocity is the best way to measure the expansion history of the universe. How we can confirm that the