The growing complexity of the Milky Way Galaxy, expressed in terms of Φm, is shown here rising slightly over its ~12 Gy existence to date during the physical-evolutionary phase of cosmic evolution. According to the hierarchical theory of galaxy construction, dwarf galaxies and pregalactic clumps of gas merged relatively rapidly in the earlier, denser Universe, such that within several billion years after the big bang our Galaxy had matured to nearly its present size and scale. The value of Φm for the Galaxy has continued rising ever since and will likely continue doing so, though only slightly, slowly, and episodically, as more galaxies (mostly dwarfs) collide and merge with our parent Galaxy.
