I've noticed from searching my own username on Google that there are some user profile pages on Google that rank highly despite zero backlinks (at least I assume it's 0- it's highly unlikely than anyone would naturally link to a user profile). On the other hand, I'm running some SEO testing sites... these have backlinks with my username in the anchor text... and these show up behind these 0-backlink sites. Is it some combination of age + overall pagerank of the domain? Some of these authority sites (or whatever you want to call them) are ranking for SERPs purely on internal linking(!) and with zero backlinks. This does go against some of the advice on this forum as folks will tell you to build backlinks regardless of quality (and not pay attention to domain trust/authority; granted, you won't always have control over domain trust/authority or whatever it is).
But what is "authority"? Their algorithms have to look at things objectively. Do they measure authority in link popularity (probably with some weighing for quality), etc. etc.?