Greetings all, First time poster and an absolute neophyte, please forgive my utter cluelessness in advance. So I was reading "Why does the Milky Way rotate?" (http://phys.org/news/2015-02-milky-rotate.html), and it brought to mind a question that's niggled at me every so often when my thoughts turn to such things... The linked article above repeats a rotation figure for the Milky Way I've seen before - 200 million years or thereabouts per revolution. Spiral galaxies in general exhibit a great deal of intricate detail in their structures; density wave induced arms, well-defined core bulges, the list goes on - Andromeda makes a fine example. It's pretty difficult to read an article on astronomy without tripping over a figure of it being roughly 13.7 billion years since the big bang. The 400,000 or so years until "the era of recombination" and the first stars and galaxies began to form aside, the primordial mass that became the Milky Way galaxy has had time to complete something like 60 revolutions. The question: Has anybody ever studied the dynamics of spiral galaxy formation with regard to how many revolutions are required to evolve such detailed structures? Intuitively, something doesn't seem right - it's hard to envision 60 revolutions being enough for all the observed detailed structure to form, not to mention spiral galaxies merging to form hazy ellipticals. I can certainly be wrong about that, but can anyone point me to an analysis of that question? Thanks in advance.