Primordial energy and matter flew in all directions. It cooled. Gas clouds condensed into galaxies. Galaxies are aggregates of stars, the building blocks of the universe.
Perhaps a minor consideration but as the theory of relativity states that any reference system are relatative & valid then would not the basic building blocks of the cosmos remain the basic elements which give it form?
Proof of the Big Bang came from the work of Edwin Powell Hubble. By applying the Doppler Effect to light, Hubble found that light from galaxies shows a redshift. This suggests that galaxies are receding, travelling away from each other. This is what we mean by the Expanding Universe.
Ya know I started looking at your threads to see what was being discussed related to another thread. Funny thing was it started about aspects of the changes in the seasons & extended to the alignment of the magnetic poles => lunar orbit? I was having trouble with the concept that the earth orbit maintained its alignment producing the four seasons.
Perhaps the best way to explain it is by relating it to the photo & your statement about the doppler effect. As the galaxies have a spin or rotational motion then the doppler effect would have different values according to whether the arms (outer stars) motion was toward us or away from us plus any motion of the galaxy's motion itself. Now if thegalaxy spins then the spin velocity could be interpolated but if the various stars rotote (like the planets of our solar system) then such interpolation would be arbitrary as each star's rotational velocity is arbitrary.