Switch to scale factor "time" (universe its own clock) In a sense the universe is its own clock and the pointer-hand is the scalefactor, as in: "when distances were 0.1 what they are today" "when distances were 0.3 what they are today" "when distances were 0.9 what they are today" For some purposes I think it's good to be able to switch over to thinking of time with the scalefactor (commonly denoted "a") serving as the index of change and marker of events, rather than numbers of thousand, millions and billions of years. There is a sense in which our earth years are not so meaningful, talking about the expansion process of the universe, and in which "a" is a more convenient way to keep track. Plus over much of history, from formation of the first galaxies up to present, the relation is roughly LINEAR. So, should the need arise, one might quickly reckon translations from one method of counting to the other. After thinking it over I decided to try it out. I already was doing some of that anyway: mentally marking a time or era by how big distances were compared with today. If you also want to try the experiment, the first thing we need to do is get used to thinking of recombination occurring at scale 1/1090 whatever that is, rather than at year 373,000 or whenever it was--I think using latest model parameters it was 373,000. And the first galaxies forming at around scale 1/11, rather than some number of millions of years. This might not be so easy. Let's see. 1/11 is 9 percent. Distances were 9 percent of today's. Proto-galaxies were forming, not grand spirals with thin disks like we have today, but more modest blobs of stars. That was the 9 percent "era". Maybe the most difficult number to get used to is 0.092 percent. This is the moment of recombination, when the ancient CMB light was released. When that happened, distances were 0.092 percent of present size. This could be the Achilles heel of the whole idea, 0.092 is such a dinky number. Easier to think of it as 1/1090. The prospect of having to go through life thinking of the CMB being released at scale 0.092% is discouraging, but I want to give this a fair trial. Let's figure out when the Milkyway galaxy's thin disk formed. The thin disk formed fairly recently actually, at scale 44% (translating from Wikipedia article on Milkyway formation). Milkyway has some very old stars in it, going back to the 9% era of protogalaxy formation. But its present size and structure (thin disk, flat spiral) are supposed to be more recent developments.